• Classification of Elements- The Periodic Table

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10th Class - Physical Science-TS

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10th Class - Physical Science-TS
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I. Reflections on concepts

Question 1.
What are the limitations of Mendeleeff’s periodic table? How could the modern periodic table overcome the limitations of Mendeleeff’s table?

Answer:
Limitations of Mendeleeff’s periodic table: -

  1. Position of hydrogen: The position of hydrogen in table is not certain because it can be placed in group IA as well as in group VII A as it resembles both with alkali metals of IA group and halogens of VITA group.
  2. Anomalous pair of elements: Certain elements of higher atomic mass precede those with lower atomic mass. Eg: Tellurium proceeds Iodine, potassium placed after Argon. (Atomic mass 40) .
  3. DissimIlar elements placed together: Elements with dissimilar properties were placed in same groups as sub-group A and sub-group B.
    Eg: U, Na, and K of the IA group have little resemblance with Cu, Ag, Au of IB group.
  4. Some similar elements are separated: Some similar elements like copper and mercury ‘silicon and thallium’ etc., are placed ¡n different groups of the periodic table.
Question 2.
Define the modern periodic law. Discuss the construction of the long form of the periodic table.

Answer:
Modern Periodic Law: The physical and chemical properties of elements are the periodic function of the electronic configurations of their atoms.

  1. The modern periodic table has eighteen vertical columns known as groups and seven horizontal rows known as periods.
  2. The horizontal rows of elements In a periodic table are called periods. The elements in a period have consecutive atomic numbers. The vertical columns of elements In the table are called groups.
  3. Based on which subshell the differentiating electron enters In the atom of the given element the elements are classified as s, p. d, and f block elements.

s-Block elements :- The elements with valence shell configuration ns1and ns2are s- Block elements.
p-Block elements: The elements with electronic configuration from ns2np1to ns2np6are p-block elements.
s and s block elements together are known as representative elements. d-Block elements or Transition elements:
The elements with valency electronic configuration ns2np6nd1to ns2np6(n-1) d10are called d-Block elements. These move from left to right in periodic table and we observe a transition of elements from metals to non-metals. Hence these are called transition elements.

f-Block elements or Inner transition elements: The elements In which f-orbitals are being filled in their atoms are called f-Block elements. These elements are called inner transition elements.

Inert Gases: Helium, Neon, Argon, Krypton, Xenon, Radon do not involve In any reaction and they are called Inert gases or noble gases. These are placed In zero group and every period ends with noble gas.

The long periodic table Is divided into 7 periods and 18 groups. First period contains 2 elements second period contains 8 elements. Third period contains 8 elements 4th and 5th periods contain 18 elements each and sixth period contains 32 elements. Seventh period is incomplete.

The 4f elements are called Lanthanolds. Elements from58Ce to71Lu. The 5f elements are called Actinoids from90Th58to103Lr71These are shown separately at the bottom of the periodic table.

Question 3.
Explain how the elements are classIfied Into s, p, d, and f-block elements In the periodic table and give the advantage of this kind of classification.

Answer:
Depending on the valency shell electronic configuration elements are classified into s, p, d, and f block elements.
s-Block elements: The elements with valence shell electronic configuration ns1and ns2are called s-block elements.

p-Block elements: The elements with valence shell electronic configuration ns2np6are called p-block elements. s and p block elements together known as Representative elements.

d-Biock elements : The elements with valence electronic configuration from ns2np6(n -1)d1to ns2np6(n -1)d10are called d-block elements. These are also called as Transition elements.

f-Block elements: The elements In which f-orbitaIs are being filled in their atoms are called f - block elements. These are also known as Inner Transition Elements.

Advantage: This division of elements into blocks Is useful to divide the elements into groups. Every group has the elements with same valence electronic configuration. So they have similar chemical properties.

s-block elements - I A and II A groups
p-block elements - III A to VITI A or zero group.
d-block elements - I B to VIII B groups
f-block elements - Lanthanoids and Actinoids.

Question 4.
Write down the characteristics of the element having atomic number 17.

Electronic configuration …………………….
Period number …………………….
Group number …………………….
Element family …………………….
No. of valence electrons …………………….
Valency …………………….
Metal or Non-metal …………………….

Answer:
Electronic configuration: 1s22s22p63s23p5
Period number : 3
Group number: 17
Element family: Halogen (VII A) or 17th group
No. of valency electrons : 2+5 = 7 ( seven )
Valency: 1
Metal or Non-metal : Non-metal

Question 5.
Complete the following table using the periodic table.

Answer

Question 6.
Complete the following table using the periodic table.

Answer

Question 7.
Newlands proposed the law of octaves. Mendeleeff suggested eight groups for elements in his table. How do you explain these observations in terms of modern periodic classification?

Answer:

  • Newlands proposed the law of octaves.
  • According to Newlands law of octaves, every eight element starting from a given one be a repetition of the first with regard to its properties.
  • Mendeleeff suggested eight groups for elements in his table.
  • The elements in the same group have same properties that means every eight element starting from a given element have same property with that.
  • In terms of modern concepts, after completion of one shell the properties of elements are repeated.
  • After completion of ns2 np6 configuration the properties of elements are repeated.
  • So Newlands law of octaves and Mendeleeff’s suggestion of eight groups for elements are also reliable according to modem concepts.
Question 8.
Why was the basis of classification of elements changed from the atomic mass to the atomic number?

Answer:

  1. The first attempt to classify elements was made by Dobereiner.
  2. Dobereiner’s attempt gave a clue that atomic masses could be correlated with properties of elements.
  3. Newlands’ law of octaves also followed the same basis for classification but this law Is not valid for the elements that had atomic masses higher than calcium.
  4. Mendeleeff’s classification also was based on the atomic masses of elements, but it lead to some limitations like Anomalous pair of elements and Dissimilar elements placed together.
  5. Mosley by analyzing the X-ray patterns of different elements was able to calculate the number of positive charges in the atoms of respective elements.
  6. With this analysis, Mosley realized that the atomic number is more fundamental characteristic of an element than its atomic weight.
  7. So, he arranged the elements in the periodic table according to the increasing order of their atomic number.
  8. This arrangement eliminated the problem of anomalous senes and dissimilar elements placed together In same group as done by Mendeleeff’s classification.
Question 9.
(a) What is a periodic property? How do the following properties change In a group and period? Explain.

(a) Atomic radius
(b) Ionization energy
(c) Electron affinity
(d) Electronegativity.

Answer:
Periodic property: Periodicity means that when elements are arranged according to their electronic configuration, the periodic properties of elements in the periodic table reoccur at regular intervals – such properties which reoccur are called as periodic properties.

Change of properties In a group and a period.

Type of Periodic Property Trends in
  Groups (from top to bottom) Periods (from left to right)
Atomic radius Increasing Decreasing
Ionization energy Decreasing Increasing
Electronegativity Decreasing Increasing
Electron Affinity Decreasing Increasing

Explanation:
(a) Atomic radius: Atomic radius of an element Is not possible to measure in its isolated state, because it is not possible to determine the location of the electron that surrounds the nucleus. Hence the distance between nucleus and outermost orbit of an element is taken as atomic radius measured In Pm (Pico Meters).

Variation In group: In a group as we go down, the atomic number of the element Increases, as a new shell Is added. As a result, the distance between nucleus and the outer shell Increases. This Is the reason why the atomic radius increases as we go down in a group.

Variation In period: AtomIc radii of elements decrease across a period from left to right. As we go from left to right, electrons enter into the same main shell or even Inner shell. Therefore there should be no change In the distance between nucleus and outer shell, but nuclear charge Increases. Hence the nuclear attraction on the outer shell increases. As a result the size of the atom decreases.

(b) Ionization enegry: The energy required to remove an electron from the outermost orbit or shell of a neutral gaseous atom is called ionization energy.

Variation in group: As we go down in a group, atomic radius increases. Hence the ionization energy decreases from top to bottom.

Variation In period: As we go from left to right in a period, the atomic radius decreases. Hence the ionization energy increases from left to right In a period but does not follow gradient order as the electron is attracted more towards the nucleus.

(c) Electron affinity: The electron affinity of an element is defined as the energy liberated when an electron Is added to its neutral gaseous atom. Electron affinity of arm atom is also called electron gain enthalpy of that element.

Variation in group: Electron gain enthalpy values decrease as we go down In a group, due to Increase In atomic radius.

Variation In period: Electron gain enthalpy values Increase as we go from left to right in a period, due to decrease in atomic radius.

(d) Electronegativity: The electronegativity of an element Is defined as the relative tendency of its atom to attract electrons towards itself when it is bounded to the atom of another element.

Variation in groups and periods: Electronegativity values of elements decrease as we go down in a group and increase along a period from left to right.

Question 10.

(b) Explain the ionization energy order In the following sets of elements.
(a) Na, Al, Cl
(b) Li, Be, B
(c) C, N, O
(d) F, Ne, Na
(e) Be, Mg, Ca.

Answer:

(a) Na, Al, Cl: All these three elements belong to same period. The order of their atomic size Is Na > Al> Cl. As we move from left to right in a period Ionization energy increases
∴ The order of ionization energy of these elements is Cl> Al> Na.

(b) Li, Be, B: U, Be, B belong to same period. The electronic configuration of Li-1S22S1, Be-1S22S2, B-1S22S22p1. The penetration power of 2P is less when compared to 2s. So it is easy to remove electrons from ‘2p’.
∴ The order of ionization energy of these elements is: Be > Li> B.

(c) C, N, O : C, N, O belong to same period. The electronic configuration of C - 1s22s22p2, N-1s22s22p3, O-1s22s22p4. Nitrogen has half filled degenerate orbital configuration. So, it Is more stable compared to Cl and ‘O’so Its Ionisation energy Is high.
∴ Order of ionization energy of these elements is: N > C> O.

(d) F, Ne, Na: Electronic configuration of F -1S22s22p5; Ne - 1S22S22p6; Na - 1s22s22p63s1. Ne is an Inert gas, so It has highest Ionization energy.
‘Na’ has smaller size compared to F. So ¡t ha high ionization energy.
∴ The order of ionization energy is: Ne>F>Na.

(e) Be, Mg, CaP: These elements belong to the same group the atomic size of these elements Is In the order of Ca > Mg > Be. As atomic size increases ionization energy decreases. The order of Ionization energy Is Be > Mg > Ca.

Application Of Concepts

Question 1.
Given below Is the electronic configuration of elements A, B, C, and D.

(A) 1s22s21. WhIch are the elements coming within the same period?
(B) 1s22s22p63s22. Which are the ones coming within the same group?
(C) 1s22s22p63s23p33. Which are the noble gas elements?
(D) 1s22s22p64. To which group and period does the clement C ‘belong?

Answer:
(1) A and D belong to same penned B and C belong to the same period.
(2) A, B coming in the same group.
(3) D is the noble gas.
(4) C’ belongs to 15th group and third period.

Question 2.
s - block, and p - block elements (except 18th group elements) are sometimes called as ‘Representative elements’ based on their abundant availability In the nature. Is It Justified? Why?

Answer:

  • s-block and p-block elements (except 18th group elements) are called ‘Representative elements’.
  • All these elements have incomplete outermost shells.
  • So they are chemically reactive to obtain stable electronic configuration of noble gases ns2np6.
  • So, they are abundant In nature n the form of compounds.
Question 3.
The electronic configuration of the elements X, Y, and Z are given below.

(A) X = 2 (B) Y = 2, 6 (C) Z =2, 8, 2
(i) Which element belongs to second period?

Answer:
‘Y’ belongs to the second period. Because differentiating electron enters into second shell.
(ii) Which element belongs to second group?

Answer:
Element ‘Z’ belongs to second group. Because its valence is ‘2’.
(iii) Which element belongs to 18 group?

Answer:
Element X belongs to 18th” group because its 1st shell is completely filled with electrons.

Question 4.
(a) State the number of valence electrons, the group number and the period number of each element given in the following table.

Answer:

Element Valence electrons Group number Period number
Sulphur 6 16 (VIA) 3
Oxygen 6 16(VLA) 2
Magnesium 2 2 ( II A) 3
Hydrogen 1 No group 1
FluorIne 7 17 ( VII A) 2
Aluminium 3 13 (III A) 3

(b) State whether the following elements belong to a Group (G), Period (P) or Neither Group nor Period Indicating the letters G or P or N

Answer:

Elements Group / Period / Neither group nor period
Li, C, O P
Mg, Ca, Ba G
Br, Cl, F G
C, S, Br N
Al, SI, Cl P
Li, Na, K G
C, N, O P
K, Ca, Br N
Question 5.
Identify the element that has the larger atomic radius In each pair of the following and mark it with a symbol (?).

(i) Mg, Ca
(ii) Li, Cs
(iii) N, P
(iv) B, AI

Answer:

  1. Mg, Ca: Calcium has large atomic radius. Since Mg and Ca are in same group Ca falling below Mg. Atomic radius increases from top to bottom In a group.
  2. Li, Cs: Cs has large atomic radius as Li and Cs are also in the same group and Cs lying below Li.
  3. N, P: Phosphorous has large atomic radius. As N and P are also In the same group and P lying below N.
  4. B, AI: Al has large atomic radius. B, Al are in same group III A and Al is below B.
Question 6.
Identify the element that has the lower Ionization energy in each pair of the following and mark it with a symbol (?).

(i) Mg, Na
(ii) Li, O
(iii) Br, F
(iv) K, Br

Answer:

  1. Mg, Na: Na has low ionization energy. Since Mg, Na are in same period ionization energy increases from left to right. Na lies left to Mg. So Na has lower ionization energy.
  2. Li, O: Li has lower ionization energy. U lies left to ‘O’ in 2nd period.
  3. Br, F: Bromine has lower ionization energy; Br & F are in same group. IE decreases from top to bottom. Bromine is below F. So It has lower lE.
  4. K, Br: ‘K’ has lower ionization energy. Since it is left to Br in the same period.
Question 7.
How does metallic character change when we move

(i) Down in a group?
(ii) Across a period?

Answer:
(i) Down in a group?
Metallic character increases when we move down the group.
(ii) Across a period?

Answer:
Metallic character decreases when we move along a period.

Question 8.
On the bails of atomic numbers predict to which block the elements with atomic number 9, 37, 46 and 64 belong to?

Answer:

  1. Electronic configuration of element with atomic number 9 is 2, 7 – belongs to p-block.
  2. Electronic configuration of element with atomic number 37 is 2, 8, 8, 18, 1 – belongs to s- block.
  3. Electronic configuration of element with atomic number 46 is 2, 8, 8, 18, 10 – belongs to d – block.
  4. Electronic configuration of element with atomic number 64 Is 2, 8, 8, 18, 18, 10 -belongs tO f – block.
Question 9.
Using the periodic table, predict the formula of compound formed between an element X of group 13 and another element Y of group 16.

Answer:
Element X of group 13 Element Y of group 16
Valency of element X = 3 Valency of element Y
18-16=2

Compound: X2Y3

Question 10.
An element has atomic number 19. Where would you expect this element in the periodic table and why?

Answer:
The element with atomic number 19 is in 4th’ period and first group of periodic table.
Reason:

  1. Electronic configuration : Is22s22p63s23p64s1’.
  2. The differentiating electron enters Into 4t shell. Hence it belongs to 4th period.
  3. The differentiating electron is In ‘s’ orbital. So it belongs to ‘s’ block.
  4. The outermost orbital has only one electron. Hence it belongs to first group.
Question 11.
Elements In a group generally possess similar properties, but elements along a period have different properties. How do you explain this statement?

Answer:

  1. Physical and chemical properties of elements are related to their electronic configurations, particularly the outer shell configurations.
  2. The atoms of the elements in a group possess similar electronic configurations. Therefore, we expect all the elements in a group should have similar chemical properties and there should be a regular gradation in their physical properties from top to bottom.
  3. But in a period from left to right, elements get an increase in the atomic number by one unit between any two successive elements.
  4. Therefore, the electronic configuration of valence shell of any two elements in a given period is not same. Due to this reason elements along a period possess different chemical properties with regular gradation in their physical properties from left to right.
Question 12.
Name two elements that you would expect to have chemical properties similar to Mg. What is the basis for your choice?

Answer:

  • Calcium (Ca) and Stranúum (Sr) are the two elements, which are similar to Mg in chemical properties.
  • Because they belong to the same group lIA. Ail the elements which are in the same group have same electronic configuration and same chemical properties.
Question 13.
An element X belongs to 3rd perIod and group 2 of the periodic table. State (a) The no. of valence electrons in it (b) The valency (C) Whether It is metal or a non-metal.

Answer:
The element ‘X’ belongs to 3rd peñad and group 2 is Mg.
(a) The no.of valence electrons 2.
(b) The valency = 2.
(c) It is a metal.

Question 14.
How do you appreciate the role of electronic configuration of the atoms of elements In perIodic classification?

Answer:

  1. According to Modern Periodic Iaw the properties of elements are the functions of their atomic number or electronic configuration”.
  2. Elements having same number of valence electrons are placed in the same group based on their electronic configuration.
  3. So, we can easily locate the position of any element in the periodic table with Its electronic configuration.
  4. Hence electronic configuration plays a major role In the preparation of Modern period table. So its role is thoroughly appreciated.
Question 15.
Without knowing the electronic configurations of the atoms of elements Mendeleeff still could arrange the elements nearly close to the arrangements in the modern periodic table. How can you appreciate this?

Answer:

  1. Mendeleeff’s vision must be appreciable because he left some gaps predicting the existing of some elements, which are not available at that time.
  2. Atomic weights of some elements can be corrected by placing them In correct places.
  3. If we compare the long-form periodic table with Mendeleeff’s table, we find many elements with their places unchanged.
  4. One can see from these discussions, that the Mendeleeffs accurate prediction and their eventual success made him and his classification of elements famous, Even today his table of elements Is followed with minimum modifications.
Question 16.
Comment on the position of hydrogen in periodic table.

Answer:

  1. The configuration of Hydrogen (1s1) Is responsible for its dual nature.
  2. Either the electron can be lost behaving as electropositive elements (H+) like alkali metals or the electron can be gained as to complete, is subshell behaving as electronegative element (H–) like halogens.
  3. The position of Hydrogen is not fixed in the periodic table sometimes it is placed with alkali metals and sometimes with halogens.
  4. However, Hydrogen exhibits other properties which differ from both alkali metals and halogens.

Higher Order Thinking Questions

Question 1.
How does the positions of elements In the periodic table help you to predict Its chemical properties? Explain with an example.

Answer:

  1. The physical and chemical properties of atoms of the elements depend on their electronic configuration, particularly the outer shell configurations.
  2. Elements are placed in the periodic table according to the increasing order of their electronic configuration.
  3. The elements In a group possess similar electronic configurations. Therefore all the elements in a group should have similar chemical properties.

Eg: Consider K

  • It is the element In 4th’ period 1st’ group.
  • It is on left side of the periodic table. Hence It Is a metal.
  • It is ready to lose an electron to get octet configuration. Hence its reactivity is more.
  • It is Alkali metal.
  • All alkali metals react with both acids and bases and release H2 gas.
Question 2.
In period 2, element X is to the right of element Y. Then find which of the elements have

(i) Low nuclear charge
(ii) Low atomic size
(iii) High Ionisation energy
(iv) High electronegativity
(v) More metallic character.

Answer:
X s to the right of Y. So they will be YX
(i) Low nuclear charge: Nuclear charge increases from left to right in a period. So Y has low nuclear charge.
(ii) Low atomic size: Atomic size decreases from left to right in a period. So X has low atomic size.
(iii) High ionization energy: Ionization energy increases across a period from left to right. So X has high ionization energy.
(iv) More metallic character: Metallic nature decreases from left to right. So Y has more metallic character.

Suggested Experiments

Question 1.
Aluminium does not react with water at room temperature but reacts with both dil. HCl and NaOH solutions. Verify these statements experimentally. Write your observations with chemical equations. From these observations, can we conclude that Al is a metalloid?

Answer:
1. Aluminum reacts with dii. HCl and releases hydrogen gas with formation of Aluminium chloride.

2. Aluminium reacts with NaOH solution and releases hydrogen gas.

Suggested Projects

Question 1.
Collect the Information about reactivity of VIII A group elements (noble gases) from your school library and prepare a report on their special character when compared to other elements of periodic table.

Answer:

  1. The elements of Group VIII A (noble gases) are chemically inactive, because all of them have stable “Octet” configurations, except He.
  2. He has two electrons in the outermost orbital, i.e., is orbitalis is the maximum, the is orbital can accommodate. Hence “He” is also inactive.
  3. The losing or gaining an electron or sharing of electrons is difficult due to high I.E. and zero E.A value of inert gases.
  4. Under suitable conditions, the heavier elements of the group form compounds with F2and O2 or XeF2 or XeO2F2.
  5. Ar forms coordination compounds with BF3whose composition is Ar.n.BF3
  6. Xenon Hexa fluoro platinate (IV)(Xe[PtF6]) was prepared by N.Barltel. This was the first compounds of inert gases. After this compounds of Xenon with F2 and O2 were prepared.
  7. The compounds of inert gases have found varied applications in recent times.
Question 2.
Collect information regarding metallic character of elements of IA group and prepare report to support the idea of metallic character increases In a group as we move from top to bottom.

Answer:
Group IA elements are Li, Na, K, Rb, Cs, and Fr

1. Metallic character is the name given to the set of chemical properties associated with elements that are metals.

2. Chemical characteristics of metals include the following

  • form cations in ionic compounds with non-metals.
  • have ionic halides.
  • have ionic hydrides containing the H’ ion.
  • have basic oxides.

3. The elements with less electronegative character are metals.
4. All IA group elements have less electronegative characters because they are ready to lose one electron to get octet configuration.
5. If we observe this group, we can find that

Reaction with non-metals:
4M + O2→ 2M2O. In this cation is M+
Hydrides:

M stands for alkali metal.
Order of ionic nature of hydrides Is LiH < NaH < KH < RbH < CSH
Halides:
2M+X2→ 2MX
where M stands for alkali metal and X stands for halogen.
All the metal halides are ionic.

Oxides:
4M + O2→ 2M2O
But, 4 Li + O2→‘ 2 Li2O2
All metals form peroxides.
6. From the above reactions we conclude that Group IA elements are metals and their metallic character increases as we go down in the group.

Page 124

Question 1.
Can you establish the same relationship with the set of elements given in the remaining rows?

Answer:
Yes, we can establish the same relationship with the set of elements given in the remaining rows.

Question 2.
Find average atomic weights of first and third elements ¡n each row and compare It with the atomic weight of the middle element.

Answer:

Question 3.
What do you observe?

Answer:
Dobereiner’s attempts gave a clue that atomic masses could be correlated with properties of elements.

Page 137

Question 4.
Find out the valencies of first 20 elements.

Answer:

Element Valency
1.Hydrogen 1
2. Helium 0
3. Lithium 1
4. Berflium 2
5. Boron 3
6. Carbon 4
7. Nitrogen 3
8. Oxygen 2
9. Fluorine 1
10. Neon 0
11. Sodium 1
12. Magnesium 2
13. Aluminium 3
14. Silicon 4
15. Phosphorous 3, 5
16. Sulphur 2, 6
17. Chlorine 1
18. Argon 0
19. Potassium 1
20. Calcium 2

(b) How does the valency vary in a period on going from left to right?

Answer:
The valency increases from 1 to 4 and then decreases to zero as we move from left to right in a period with respect to Hydrogen. The valency increases from 1 to 7 with respect to oxygen, in a period from left to right.

(c) How does the valency vary on going down a group?

Answer:
The valency remains same in a group.

Page 139

Question 5.
Do the atom of an element and Its Ion have same size?

Answer:
No, the atom of an element and its ion do not have the same size. The size of cation is less than its neutral atom and size of anion Is greater than its neutral atom.

Think And Discuss

Question 1.
What relation about elements did Doberelner wanted to establish?

Answer:
The relative atomic mass of the middle element En each triad is nearer to the average of the relative atomic masses of other two elements. This is what Doberelner wanted to establish.

Question 2.
The densities of Calcium (Ca) and Barium (Ba) are 1.55 and 3.51gm/ cm3 respectively. Based on Doberolner’s law of triads can you give the approximate density of strontium (Sr)?

Answer:
The density of strontium = (1.55 + 3.51 )/2 = 5.06 / 2 = 2.53gm/cm3

Question 3.
Do you know why Newland’s proposed the law of octaves? Explain your answer In terms of the structure of atom.

Answer:
Newlands proposed the law of octaves. According to this law, every 8” element starting from a given elements resembles in its properties to that of starting element with the elements with similar chemical properties are to be present along horizontal.

In modem periodic table, every period starts with a new shell and ends when the shell is filled. We know about octet configuration. Newlands law of octaves Is similar to octet. configuration.

Question 4.
Do you think that Newlands law of octaves is correct? JustIfy.

Answer:
Newlands law of octaves is corretc. Mendeleeff also suggested only 8 groups in his table. Later it was discovered that eighth element has the same properties as the first one.

Question 5.
Why Mendeleeff had to leave certain blank spaces In his periodic table. What is your explanation for this?

Answer:
Based on the arrangement of the elements in the table, he predicted that some elements were missing and left blank spaces at the appropriate places In the table. Mendeleeff believed that some new elements would be discovered definitely. He predicted the properties of these new additional elements in advance purely depending on his table. His predicted properties were almost the same as the observed properties of those elements after their discovery.

Question 6.
What is your understanding about Ea2O3 and EsO2?

Answer:
Ea2O3 is the predicted formula of oxide,of the predicted element In eka – Aluminium group, This is similar to Ga2O3, the observed property of oxide of Gallum, which was discovered in 1875. EsO2 is the predicted formula of oxide of predicted element In eka-silicon group. This is similar to GeO2, the observed property of oxide of Germanium, which was discovered in.1886.

Question 7.
All alkali metals are solids but hydrogen is a gas with diatomic molecules. Do you justify the inclusion of hydrogen in first group with alkali metals?

Answer:
The similarity of hydrogen with alkali metals is ns’ configuration and ability to exhibit +1 oxidation state. Hydrogen, because of its small size and high electronegativity, it is a non-metal with high I.P. It shares one electron with another hydrogen and forms diatomic molecules. Due to weak van der Waals forces of attraction It is a gas whereas in alkali metals, metallic bond is present hence they are solids. Hence, hydrogen cant be included in first group along with alkali metals.

Question 8.
Why lanthanoids and actinoids placed separately at the bottom of the periodic table?

Answer:
Lanthanolds and actinoids are placed separately in the periodic table to maintain its structure and to preserve the principle of classification with similar properties in a single column.

Question 9.
If they are inserted within the table imagine how the table would be?

Answer:
If f-block elements are inserted within the table, the table would be too long.

Question 10.
Second Ionization energy of an element is higher than Its first ionization energy. Why?

Answer:
The required to remove first electron from the outermost orbit or shell of a neutral gaseous atom is called first ionization energy (IE1).
The energy required to remove an electron from uni-positive ion is called the 2nd ionization energy (IE2).
The second ionization energy (IE2) is greater than the first ionization energy (IE1). On removing an electron from an atom, the uni-positive ion formed will have more effective nudear charge than the neutral atom. This decreases the repulsion between the electrons and at the same time increases the nuclear attraction on the electron in the outer shells. As a result, more energy is required to remove an electron from the uni-positive ion. Hence the second ionization
energy is greater than the first ionization energy.

Question 11.
The calculated electron gain enthalpy values for alkaline earth metals and noble gases are positive. How can you explain this?

Answer:
Due to completely filled s-subshell in alkaline earth metals and completely filled valence shell (i.e. octet) in noble gases, they are highly stable. Hence energy Is required to add an electron I.e their electron gain enthalpy values are positive.

Question 12.
The second-period element, for example, F has less electron gaIn enthalpy than the third-period element of the same group for example ‘Cl’. Why?

Answer:
The atomic size of second period elements decreases and electron number increases as we move from left to right. Because of this elements of N, O, F possess vert small size and high electron density. Hence incoming electron feels repulsion due to existing electrons. Because of this, electron gain enthalpy
is less for second-period element compared to third period of the same group (In 5th’ , 6th and 7th groups).

Activity 1

Question 1.
Observe the following table and till It.

Answer:

Observations:
a) Can you establish the same relationship with the set of elements given In the remaining rows?

Answer:
Except in the first row, we cannot establish the relationship as said by law of triads.
b) Find average atomic weights of first and third elements in each row and compare It with the atomic weights of the middle element.

Answer:
From table we observe that. except Group A, in the remaining Groups, the average of atomic weights of first and third elements is roughly equal to the middle elements.

c) What do you observe?

Answer:
Dobereiner’s attempt gave a clue that atomic mass could be correlated with properties of elements.

Activity 2

Question 2.
Write the different chemical families and write involved, valency of the family.

Answer:

Question 3.
(a) Find out the valencies of first 20 elements.
(b) How does the valency vary in a period on going from left to right?
(c) How does the valency vary on going down a group?

Answer:

Element Valency
1.Hydrogen 1
2. Helium 0
3. Lithium 1
4. Berflium 2
5. Boron 3
6. Carbon 4
7. Nitrogen 3
8. Oxygen 2
9. Fluorine 1
10. Neon 0
11. Sodium 1
12. Magnesium 2
13. Aluminium 3
14. Silicon 4
15. Phosphorous 3, 5
16. Sulphur 2, 6
17. Chlorine 1
18. Argon 0
19. Potassium 1
20. Calcium 2

(b) How does the valency vary in a period on going from left to right?

Answer:
The valency increases from 1 to 4 and then decreases to zero as we move from left to right in a period with respect to Hydrogen. The valency increases from 1 to 7 with respect to oxygen, in a period from left to right.

(c) How does the valency vary on going down a group?

Answer:
The valency remains same in a group.

Important Question

TS 10th Class Physical Science Important Questions Chapter 7 Classification of Elements- The Periodic Table

1 Mark Questions

Question 1.
Define element’ according to Boyle.

Answer:
Robert Boyle defined an element as any substance that cannot be decomposed into a further simple substance by a physical or chemical change.

Question 2.
State law of triads.

Answer:
Dobereiner stated that when elements with similar properties are taken three at a time and arranged in the ascending order of their atomic weights the atomic weight of the middle element Is the average of the atomic weights of the first and third elements.

Question 3.
What are the limitations of Doberelner’s law of trade?

Answer:
All the known elements then could not be arranged in the form of triads.
The law failed for very low mass or for very high mass elements.
As the techniques improved for measuring atomic masses accurately, the law was unable to remain strictly valid.

Question 4.
State the law of octaves.

Answer:
The law of octaves states that when elements are arranged In the ascending order of their atomic weights, they fall Into a pattern in which their properties repeat at regular Intervals. Every 8th element starting from a given element resembles In Its properties to that of the starting element. This is similar to octve notes In musical scale.

Question 5.
What are the limitations for Newlands’ law of octaves?

Answer:
There are instances of two elements fitted into the same slot. Eg: Co and Ni.
Certain elements totally are dissimilar n their properties, were fitted into the same group.
The law was not valid for elements that had atomic masses higher than that of Calcium.
It was restricted to 56 elements and did not leave any room for new elements.

Question 6.
What is Doberelner triad ? Give two examples to It.

Answer:
A group of three elements In which atomic weight of middle element is average of first and third element is called Dobereiner triad.
Eg:
1) Li,Na,K
2) Cl,Br,I

Question 7.
What is Mendeleeffs periodic law?

Answer:
Mendeleeffs periodic law: The physical and chemical properties of the elements are the periodic functions of their atomic weights.

Question 8.
What is valency?

Answer:
The combining power of elements with respect to hydrogen, oxygen or indirectly any other element through hydrogen and oxygen is called valency.

Question 9.
What is modern periodic law?

Answer:
Modern periodic law: The properties of elements are periodic functions of their atomic numbers.

Question 10.
What is the name given to 1(A) group elements?

Answer:
Alkali metal family, because aliqulli plant ashes. Na; K etc., were obtained from plant ash.

Question 11.
What are halogens?

Answer:
Fluorine, Chlorine, Bromine, Iodine, and Astatine of VII A group elements are called halogens, which are obtained from sea salt.

Question 12.
What are noble gases?

Answer:
The elements of group VIII A(18) are chemically least reactive. So they are called as noble gases. Their group electronic configuration ns2np6 (except) for helium it is Is2.

Question 13.
What are Lanthanides?

Answer:
Elements acquiring same properties are called lanthanides i.e., 4f elements. They are from 58Ce(Cenum) to 71Lu(Lutetium).

Question 14.
What are Actinides?

Answer:
Elements acquiring different properties are called actinides i.e., 5f elements. They are from 90Th(Thorium) to 103 Lr(Lawrencium).

Question 15.
What are metals and non-metals?

Answer:
The elements with three or less electrons in the outer shell are considered to be metals and the ones with five or more electrons in the outer shell are considered to be non-metals.

Question 16.
What is electronegativity?

Answer:
The relative tendency of its atom to attract electrons towards Itself when it is bounded to the atom or another element is called electronegativity.

Question 17.
What is electropositive character?

Answer:
The tendency of metals to remain positive Ions in compounds is called electropositive character.

Question 18.
What are metalloids?

Answer:
Metalloids or semi-metals are elements which have properties that are intermediate between the properties of metals and non-metals. They possess properties like metals but brittle like non-metals. They are generally semiconductors. Eg: B, Si, Ge, etc.

Question 19.
Why the elements in a group have similar chemical properties?

Answer:
Physical and chemical properties of elements are related to their electronic configurations, particularly the outer shell configurations. The atoms of the elements in a group possess similar electronic configurations. Therefore we expect all the elements In a group should have similar chemical properties.

Question 20.
Why the elements In a period possess different chemical properties?

Answer:
Across the table i.e. from left to right in any period elements get an increase in atomic number by one unit between any two successive elements. Therefore, the electron configuration of valence shell of any two elements in a given period is not same. Due to this reason, elements along a period possess different
chemical properties.

Question 21.
Define atomic radius.

Answer:
Atomic radius is the distance between the centre of the atomic nucleus and the electron cloud of the outermost energy level.

Question 22.
What is crystal radius (or) metallic radius?

Answer:
Half o, the distance between the centres of the nudei of two adjacent metal atoms In the metallic crystal is called crystal radius or metallic radius.

Question 23.
What is covalent radius?

Answer:
Covalent radius is half of the distance between the nuclei of two atoms, held together by a covalent bond In a homo-atomic molecule.

Question 24.
How does the atomic radius vary in a group and a period?

Answer:
In a group as we go down, the atomic radius Increases, and In a period, as we move from left to right, the atomic radius decreases.

Question 25.
Define IonIzation energy.

Answer:
The energy required to remove an electron from the outermost orbit or shell of a neutral gaseous atom is called Ionization energy.

Question 26.
How does the Ionization energy vary In group and period?

Answer:
In a group as we move down, Ionization energy decreases and in a period, as we move from left to right, the Ionization energy increases, but does not follow gradient order.

Question 27.
Define electron affinity.

Answer:
The electron affinity of an element is defined as the energy liberated when an electron Is added to its neutral gaseous atom. Electron affinity of an element is also known as electron gain enthalpy of that element.

Question 28.
How does the electron gain enthalpy values vary in a group and a period?

Answer:
Electron gain enthalpy values decrease as we go down in a group and increase along a period from left to right.

Question 29.
What is the Milliken’s proposal about electronegativity?

Answer:
Milliken proposed that the electronegativity of an element is the average value of its ionization energy and electron affinity.
Electronegativlty = Ionization energy + Electron affinity/2

Question 30.
How do the electronegativity vary In a group and in a period?

Answer:
Electronegativity values of elements decrease as we go down in a group and increase along a period from left to right.

Question 31.
How does metallic and non-metallic characters vary In a group and period?

Answer:
Metallic character increases while non-metallic character decreases in a group as we move from top to bottom.
Metallic character decreases while non-metallic character increases in a period as we move from left to right.

Question 32.
Give example(s) where the electronic configuration of an element does not JustIfy Its Inclusion In a block of element.

Answer:
He (1s2) is Included in p-block elements.
H (1s1) is not given any specific place. It can be also studied along with p- block halogens.

Question 33.
How many elements are present In the 5th period of the long-form periodic table? Give a possible reason.

Answer:
The 5th period starts with the filling of 5s level. It ends when the 5p level Is complete. The sub-energy levels filled in the sequence are 5s, 4d, 5p. Then the total number of electrons filled into these levels is 18. Hence the total number of elements in the period Is 18. The period starts with Rubidium (Rb) and ends with Xenon (Xe).

Question 34.
What do you mean by screening effect?

Answer:
The influence of the inner core of electrons on the attraction of the nucleus towards outer electrons is referred as "shielding effect’ or "screening effect".

Question 35.
Arrange the elements B, N, Be and O in the increasing order of their ionizatIon potentials.

Answer:
The increasing order of ionization energy of B, N, Be and O is 0 < N

Question 36.
What is meant by first Ionization energy?

Answer:
The energy required to remove first electron from the outermost orbit or shell of a neutral gaseous atom Is called first Ionization energy (1E1)

Question 37.
What is meant by second Ionization energy?

Answer:
The energy required to remove an electron from a uni-positive ion is called the second Ionization energy (1E2).

Question 38.
What do you mean by element family?

Answer:
Group of elements Is also called element family or chemical family. Eg: Group 1 (IA) is from Li to Fr with outer shell configuration ns ‘ad is called Alkali metal family.

Question 39.
Give the outer orbits’ general electronic configuration of the following types of elements, a) Noble gases b) Representative elements c) Transition elements d) Inner transition elements.

Answer:
The general electronic configuration of
(a) Noble gas is ns2 np6 except He. For He: 1s2
(b) Representative elements
s - block: ns1 and ns2
p - block : ns2 np1 to ns2 np5.
(c) Transition elements : (n - 1) d(0 -10) ns1or2 (where n ≥ 4)
(d) Inner transition elements : (n - 2) f1to14 (n - 1) d(1 to 6) ns2.

Question 40.
Chlorine, bromine, iodine are Doberelner’s triads. How do you justify?

Answer:
Chlorine, bromine and Iodine have similar properties and atomic weight of bromine Is average of chlorine and iodine.

Question 41.
Why are lanthanoids and actinoids placed separately at the bottom of the periodic table?

Answer:
Lanthanoids and actinoids belong to f - block elements with different properties so they placed at the bottom of periodic table.

Question 42.
Second Ionization energy of an element Is higher than Its first Ionization energy Why?

Answer:
It is difficult to remove an electron from unipositive ion when compared with neutral atom. So second ionization energy is always greater than first ionization energy.

Question 43.
Hydrogen can be placed in group 1. and group 7 periodic tables. Why?

Answer:
Hydrogen has both +1 as well as -1 oxidation states, So still, there is some ambiguity in position of hydrogen.

Question 44.
A, B are two elements. Its compound material Is A,B, then what will be the valency of A and B?

Answer:
The valency of A Island B is 2.

2 Marks Questions

Question 1.
Referring the part of the periodic table given below answer the questions that follow.
LiBeB CNOF
NaMgAlSiP SCl
a) What happens to the atomic size If moved from left to right? Support your answer.
b) What changes do you observe In the metallic properties of the elements when moved from left to right?

Answer:
a) When we move from left to right in a periodic table atomic radii of elements decrease, as a result the size of the atom decreases.
b) When we move From left to right in a periodic table electronegativity values of elements decrease, as a result the metallic properties of the elements increase.

Question 2.
The second-period element ‘F’ has electron gain enthalpy than the third-period elements of same group ‘ci’. Why?

Answer:
In a group of elements, the electron gain enthalpy decreases from top to bottom. But in general the second element in a group i.e., period element has greater electron gain enthalpy than the first element i.e. 2nd-period element.
Eg: E.An of F
This Is because Fluorine atom is smaller in size than chlorine atom. F2 is also having strong Inter electronic repulsions. In the addition of an electron to fluorine atom, the electronic repulsions overcome at the expense of a part of the energy liberated. Hence the overall energy lIberated Is less than that of chlorine atom.

Question 3.
x, y, and z are the elements of a Dobereiner’s triad. If the atomic mass of ‘z’ Is 7 and that of ‘Z’ In 39. What should be the atomic mass of the ‘Y’?

Answer:
The atomic mass of x = 7
The atomic mass of z = 39
x, y, z form Dobereiner triad
Atomic mass of y = average of x and z
= 7+39/2 = 46/2 = 23

Question 4.
Differentiate the metals and non-metals.

Answer:

MetalsNon-Metals
1. Metals have lustrous surfaces. 1. Non-metals do not have lustrous surface
2. They show malleability2. They do not show malleability
3. They show ductility.3. They do not show ductility.
4. They produce sonorous sounds.4. They do not produce sonorous sound
5. Generally they are hard.5. Generally they are soft.
6. They are good conductors of electricity.6. Generally they are bad conductors of electricity.
7. Generally they liberate hydrogen gas when they are treated with acids. 7. They do not liberate hydrogen gas.
Question 5.
How are the elements divided into s, p, d, and f - blocks in the Modern periodic table?

Answer:
Depending upon to which sub-shells the differentiating electron i.e., the last coming electron enters in the atom of the given element, the elements are classified as s, p, d, and f-block elements. Eg: 11Na.
The electronic configuration of Na is 1s22s22p63s1.
The differentiating electron gets into 3s level, Therefore 11Na belongs to s block. Similarly 13Al(1S22s22p63s23p1) belongs to p-orbital
21Sc (1s22s22p63s23p64s23d1) belongs to d-block and
58Ce (1s22s22p63s23p64s23d104p64d105s25p66s24f1) belongs to f-block.

Question 6.
Explain the limitations of Mendeleefrs’ periodic table.

Answer:
1. Anomalous pair of elements: Certain elements of highest atomic weights precede those with lower atomic weights. Eg: TellurIum (At.wt. 127.6) precedes Iodine (at. wt. 126.9).
2. Dissimilar elements placed together: Elements with dissimilar properties were placed in same group as sub-group A and sub-group B.
Eg:
1. Alkali metals like U, Na, K, etc.. of IA group have little resemblance with coinage metals like Cu, Ag, Au of lB group.
2. Cl is of VIIA group and ‘Mn’is of VII B. But chlorine Is a non-metal where as Mn is a metal.

Question 7.
Observe the Information provided in the table and answer the questions given below It.
Element NaCCaP TiNi
Atomic Number 116201522 28
(i) What are the s-block elements in the table?
(ii) What are the ‘p’ block and ‘d’ block elements In the table?

Answer:
(i) Na,Ca
(ii) C. P are p-block elements
Ti, Ni are d-block elements.

4 Marks Questions

Question 1.
Some elements belonging to second period of periodic table, and their atomic radii are given below. Observe them and write answers.
2nd period elements BBeON LiC
Atomic radii 881116674152 77
a) Write the elements in the ascending order of their atomic radii.
b) Which of the 2nd-period elements closer to the configuration of Inert gas?
C) Which is the outermost orbit of all these elements?
d) Which element’s atomic size bigger, Beryllium or Carbon? Why?

Answer:
a) The ascending order of atomic sizes is O. N, C. B, Be and Li.
b) Lithium has closest inert gas configuration i.e.. 1S22st. Its nearest inert gas is Helium.
c) The outermost orbit for all these elements is second orbit.
d) Beryllium has more atomic size than Carbon. Because when we move across a period the atomic number increases. So nuclear attraction of outermost orbit increases. So carbon has lesser size than Beryllium.

Question 2.

Refer the above part of periodic table and answer the following questions.
a) Element with the least atomic size.
b) Write th, electronic configuration of the elements B and E.
c) Identify the elements that have similar physical and chemical properties as the element Y.
d) Arranged elements increasing order of their electro-negativity values.

Answer:
a) The element with least atomic size is E. Because when we move from left to right in a period the atomic size decreases.
b) Electronic configuration of B is 1s22s22p63s23p1. Because the element belongs to 13th group its general configuration is ns2nP1 and the element belongs to third period and its atomic number is 13. Similarly electronic configuration of E ¡s 1s22s22p63s23p4. Because the element belongs to 16th group. Its general configuration is ns2np4 and third period. So its atomic number is 16.
c) The elements whid, have similar physical and chemical properties with Y are X and Z. Because they lie in a single group that Is l group. In a group, elements are having similar physical and chemical properties.
d) Z has highest atomic size because In a group atomic size Increases.

Question 3.
The electronic configuration of atom A is 2, 8, 6
a) What is the atomic number of element A?
b) State whether the atomic size of element A Is bigger or smaller than the atom having atomic number 14. Why?
c) Which of the elements exhibit similarity in chemical properties as element A 0(8), C(6), N(7), AV(1.8). Why?
d) How the element is formed Inert gas configuration?

Answer:
The electronic configuration of atom - A is 2, 8, 6.
a) Atomic number of element ‘A’ Is 16. i.e., Sulphur.
b) The atom which having atomic number - 14 is Silicon (SI). Atomic size of element decreases across periods from left to right. So the atomic size of element ‘A’ is smaller than the atom having atomic number 14.
c) Element oxygen O - exhibits similarity in chemical properties as element A, because they belong to the same group.
d) Given element - A becomes inert gas i.e., Argon configuration by gaining electrons.

Question 4.
Mendeleeff classified the then-known 63 elements in the form of a periodic table. Mention any two things that benefitted study of chemistry, to support above statement.

Answer:
Mendeleeff accepted minor inversions in the order of increasing atomic weights as these inversions resulted in elements being placed in the correct group.
It was the extraordinary thinking of Mendeleeff that made the chemists to accept the periodic table and recognize Mendeleeff more than anyone else as the originator of the periodic law.
At the time when Mendeleeff introduced his periodIc table, even electrons were not discovered.
Even then the periodic table provides a scientific base for the study of chemistry of elements.
In his honour the 101st element was named "Mendelevlum’

Question 5.
Explain the salient features and achievements of the Mendeleeff’s periodic table.

Answer:
Mendeleeff arranged the elements in the increasing order of their atomic weights.
Salient Features:
1. Groups and sub-groups: There are 8 vertical columns called groups. represented by Roman numerals Ito VIII. Each group s divided into two subgroups A and B. The elements present in a group and its subgroup have similar properties.
2. Periods: The horizontal rows In Mendeleeff’s table are caned ‘periods’. There are 7 periods, denoted by Arab numerals I to 7. A period comprises the entire range of elements after which properties repeat themselves.
3. Predicting the properties of missing elements: Based on the arrangement of the elements in the table, he predicted that some elements were missing and left blank spaces at the appropriate places in the table. He named those elements tentatively by adding the prefix ‘eka’ to the name of the element immediately above the each empty space. Eg: Eka-boron, Eka - aluminum, Eka - silicon were close to the observed properties of Scandium, Galium and Germanium respectively which were discovered later.
4. Correction of atomic weight: The correct placement of elements In Mendeleeff’s periodic table helped in correcting the atomic masses of some elements like Beryllium, Indium, Gold.
5. Anomalous series: Some anomalous series of elements like ‘Te’ and I were observed in the table. The anomalous series contained elements with more atomic weight like (Te) placed before the element with less atomic weight like I.

Question 6.
How are the elements arranged Into groups and periods In the Modern Periodic Table ? Elements in a group possess similar properties, but elements in a period do not show similarities in their properties. Why?

Answer:
1. Groups and sub-groups: There are 8 vertical columns called groups, represented by Roman numerals I to VIII. Each group is divided into two sub-groups A and B. The elements present In a group and Its sub-group have similar properties.
2. Periods: The horizontal rows in Mendeleeff’s table are called ‘periods’. There are 7 periods, denoted by Arab numerals 1 to 7. A period comprises the entire range of elements after which properties repeat themselves.
3. Physical and chemical properties of elements are related to their electronic configurations, particularly the outer shell configurations.
4. The atoms of the elements in a group possess similar electronic configurations. Therefore, we expect all the elements in a group should have similar chemical properties and there should be a regular gradation in their physical properties from top to bottom.
5. SimIlarly in a period from left to right, elements get an increase In the atomic number by one unit between any two successive elements.
6. Therefore, the electronic configuration of valence shell of any two elements in a given period is not same. Due to this reason, elements along a period possess different chemical properties with regular gradation in their physical properties from left to right.

Question 7.
Explain any four factors which influence the electron affinity (Electron Gain Enthalpy)

Answer:
All the factors which influence the ionization energy would also influence the electron gain enthalpy.
Nuclear charge: More the nuclear charge, more is the electron affinity.
Screening effect or shielding effect: More the shells with electrons between the nucleus and the valence shell, they act as screens and decrease nuclear attractIon over valence electrons. This is called the screening effect. More the screening effect less is the electron affinity.
PenetratIon power of the orbitals: Orbitais belonging to the same main shell have different penetration power towards the nucleus. For example : 4s>4p>4d>4f in the penetration. Therefore it is easier to add electrons in 4f than In 4s.
Stable configuration: It is difficult to add an electron to atoms which have stable half-filled or completely filled orbitals. So, 7N(1s2,2s2,2p3) has more electron affinity value than 10(1s2,2s2,2p4) due to its half-filled configuration.
Atomic Radius: More is the atomic radius, less is the electron affinity.

Question 8.
Define ionization energy. Explain on which factor the ionization energy depends on.

Answer:
Ionization energy: The energy required to remove an electron from the outermost orbit or shell of a neutral gaseous atom is called ionization energy.
The ionization energy of an element depends on its
1. Nuclear charge: More the nuclear charge, more is the ionization energy.
Eg: Between, Na and 7d, the chlorine atom has more ionization energy.
2. Screening effect or shielding effect: The shells with electrons between nucleus and the valence shell, act as screens and decrease nuclear attraction over valence electrons called i.e screening effect. More the screening effect, less is the Ionization energy. Eg: Between 3Li and 55Cs the element 55Cs with more inner shells has less ionization energy.
3. PenetratIon power of the orbitals: Orbitais belonging to the same main shell have different piercing power towards the nucleus.
Ex : 4s > 4p > 4d > 4f> In the penetration.
It is easier to get 4f electrons than 4s. Between 4Be (1s22s2) and 5B (1s2,2s2,2p), the element 5B has less ionization energy due to less penetration power of 2p compared to 2s.
4. Stable configuration: It is easier to remove one electron from,80 (1s2,2s2,2p4) than 7N (1s2 2s2,2p3). This is because 7N has stable half-filled configuration.
5. Atomic radius: As atomic radius Increases, the ionization energy decreases. Cg: I.E. of F is greater than that of I. because the atomic radius of I is more than that of F.

Question 9.
The atomic number of elements P, Q R, S, and T are given below :
elementPQRST
Atomic number71012419
From the above table, answer the following questions:
a) Which element among these is a non-metal?
b) Which element belongs to 3rd period of periodic table?
c) Which Is an inert gas?
d) Which two elements are chemically similar?

Answer:
The electronic configuration of the elements are as follows:
Element j P Q R S T
Atomic number 17(2,5) 10(2,8) 12(2,8,2) 4(2,2) 19(2,8,8,1)
a) Element P is a non-metal since it has five valence electrons.
b) Element R belongs to third period since it has three shells.
c) Element Q is an inert gas element since It has complete octet.
d) Elements R and S are chemically similar since they have same number of valence electrons.

Question 10.

Answer the following from the above information. (March 2018)(AS3)
a) Which element possesses the higher atomic radius In the above table?

Answer:
The element with higher atomic radius is ‘K
b) Mention two pairs of & elements which forms ionic bond?

Answer:
Na, CI,; Mg, CI, etc.
c) Name the two elements having valency 2?

Answer:
Elements having valency 2 are Be, Mg, Ca, O. S, Se, etc.
d) Which element has electronic configuration of 1s22s22p4?

Answer:
Oxygen.
Do You Know

Question 1.
Are you familiar with musical notes?

Answer:
In the Indian system of music, there are seven musical notes in a scale - sa, re ga, ma, pa, da, nL In the west, they use the notations - do, re, mi, fa, so, la, ti. Naturally, there must be some repetition of notes. Every eighth note is similar to the first one and it is the fIrst note of the next scale.

Question 2.
Do you know what Mendeleeff said about the melting point of eka Al?

Answer:
‘If I hold it in mj hand, ¡t will melt’. The melting point of Ga is 30.2°C and our body temperature 37°C.
3. At the time when Mendeleeff Introduced his periodic table even electrons were not discovered. Even then the periodic table was able to provide a scientific base for the study of chemistry of elements. In his horour the With element was named Mendelevium. (Pg1s)

Question 3.
Do you know how are the names of certain families of periodic table derived?

Answer:
Alkali metal family: aliquili = plant ashes, Na, K, etc.. were obtained from plant ash, group IA elements are called alkali metals family.
Chalcogen family: chalcogens = ore product, as the elements in group 16(VIA) form ores with metals. They are called as dialcogenous family.
Halogen family: halos sea salt, genus = produced. As most of the elements In group 17(VI1A) are obtained from nature as sea salt. They are called as halogen family.
Noble gases: as the elements of group 18(VIII-A) are chemically least active. They are called as noble gases. Their outer shell electronic configurations are basis for octet rule.
5. ‘Ide’ means ‘heir’ and it is used generally for a change like CIto Cl-. ‘Cl’ is chlorine atom and Cl- is chloride ion. ‘Oid’ means ‘the same’.
Some scientists suggest lanthanoids as 57La to 70Yb, some suggest them as 58Ce to 71Lu and some take 57La to 71Lu (15 elements). There is another argument that even 21Sc and 39Y should be included In lanthanoids. All these suggestions have substance because 21Sc, 39Y and 57La to 71Lu all have the similar outer shells configurations.
Also in the case of actinoids. There are different arguments like actinoids are from 90Th to 103Lr or 89Ac to 102No or 89Ac to 103Lr. (Pg135)

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