NIOS Class 12 Chemistry Chapter 3 Periodic Table and Periodicity in Properties

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NIOS Class 12 Chemistry Chapter 3 Periodic Table and Periodicity in Properties

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Periodic Table and Periodicity in Properties

Chapter: 3

Module – II: Atomic Structure and Chemical Bonding

INTEXT QUESTIONS 3.1

1. Classify the elements of group 14, 15 and 16 into metals, non-metals and metalloids.

Ans:

Metals	Non metals	Metalloids
Sn, Pb	C	Si, Ge
Sn, Pb	N, P	As
Te, Po	O,S	Se

2. Compare the metallic character of aluminium and potassium.

Ans: Potassium is more metallic than aluminum.

3. Name the group number for the following type of clements:

(i) Alkaline earth metals.

(ii) Alkali metals.

(iii) Transition metals.

(iv) Halogens.

(v) Noble gases.

Ans: (i) 2 

(ii) 1

(iii) 3 – 12 

(iv) 17

(v) 18

4. Name five man made elements.

Ans: Np, Lr, No, Rf, Hs.

INTEXT QUESTION 3.2

1. Write the names of the elements with atomic numbers 105, 109, 112, 115 according to IUPAC nomenclature.

Ans: (i) Unnilpentium.

(ii) unnilennium.

(iii) Ununbium.

(iv) Ununpentium.

2. Arrange the following in the order of increasing size:

Na+, Al³⁺, O^2–, F^–

Ans: Al³⁺, Na⁺ , F^– , O^2–

3. How does the size of atoms vary from left to right in a period and on descending a group in the periodic table?

Ans: The atomic size decreases from left to right across a period and increases on moving down the group.

INTEXT QUESTIONS 3.3

1. What is the correlation between atomic size and ionization enthalpy.

Ans: Ionization enthalpy decreases with increase in atomic size and vice-versa.

2. Which species, in each pair is expected to have higher ionization enthalpy.

(i) ₃Li, _¹¹Na

(ii) ₇N, ₁₅P

(iii) ₂₀Ca, ¹²Mg

(iv) ₁₃Al, ₁₄Si

(v) ₁₇Cl, ₁₈Ar

(vi) ₁₈Ar, ₁₉K

(vii)₁₃Al, ₁₄C

Ans: (i) ₃Li 

(ii) ₇N

(iii) ₁₂Mg

(iv) ₁₄Si 

(v) ₁₈Ar 

(vi) ₁₈Ar

(vii) ₆C

3. Account for the fact that there is a decrease in first ionization enthalpy from Be to B and Mg to Al.

Ans: The electronic configuration of Be is 1s² 2s² whereas that of B is 1s² 2s² 2p¹. In case of Be, the electron is to be removed from completely filled s orbital whereas in case of B it is to be removed from a singly occupied p orbital. Fully-filled orbitals are more stable. Hence, ionization enthalpy decreases from Be to B. Similarly it decreases from Mg to Al.

4. Why is the ionization enthalpy of the noble gases highest in their respective periods?

Ans: The noble gases have completely filled valence shells, which makes them very stable. Their electrons are held very strongly by the nucleus. Therefore, a large amount of energy is required to remove an electron from a noble gas atom. Hence, noble gases have the highest ionization enthalpy in their respective periods.

5. Name the most electronegative element.

Ans: Fluorine.