Classification of Elements and Periodicity in Prop

3.34. Statement (b) is incorrect.

3.33. In the modern periodic table, each period begins with the filling of a new shell. Therefore, the period indicates the value of principal quantum number. Thus, option (c) is correct.

3.32.  (a) LiO₂ (Lithium oxide)

(b) Mg₃N₂ (Magnesium nitride)

(c) AlI₃ (Aluminium iodide)

(d) SiO₂ (Silicon dioxide)

(e) Phosphorous pentafluoride (f) Z = 71

(f) The element is Lutenium (Lu). Electronic configuration [Xe] 4 f7 5d1 6s2.

With fluorine it will form a binary compound = LuF₃.

3.29.  (i) s-Block elements: ns^1-2 where n = 2-7.

(ii) p-Block elements: ns² np^1-6 where n = 2-6.

(iii) d-Block elements: (n-1)d^1-10 ns ^0-2  where n = 4-7.

(iv) f-Block elements: (n-2)f^0-14  (n-1)d^0-1 ns²where n = 6-7.

3.28. The elements of Group I have only one electron in their respective valence shells and thus have a strong tendency to lose this electron. The tendency to lose electrons in turn, depends upon the ionization enthalpy. Since the ionization enthalpy decreases down the group therefore, the reactivity of group 1 elements increases in the order Li < Na < K < Rb < Cs. In contrast, the elements of group 17 have seven electrons in their respective valence shells and thus have strong tendency to accept one more electron to make stable configuration. So for group 17, the electron gain enthalpy and electronegativity decreases down the group and thus the reactivity also decreases.

3.27.  (a) Element belonging to nitrogen family (group 15) e.g., nitrogen.

(b) Element belonging to alkaline earth family (group 2) e.g., magnesium.

(c) Element belonging to oxygen family (group 16) e.g., oxygen.

3.26. 

3.25. Isotopes have same number of electrons and protons, only the number of neutrons is different. The atomic number remains the same and only atomic mass differs. Hence the ionization energy of the isotopes of a chemical element remains the same.

3.24.  (a) Gain of an electron leads to the formation of an anion. The size of an anion will be larger than that of the parent atom because the addition of one or more electrons would result in increased repulsion among electrons and decrease in effective nuclear charge.

(b) Loss of an electron from an atom results in the formation of a cation. A cation is smaller than its parent atom because it has former electrons while its nuclear charge remains the same.