Ncert Solutions Chemistry Class 11th

3.21. When an electron is added to oxygen atom, energy is released to form a negative ion. This enthalpy change called the first electron gain enthalpy is thus negative. On adding another electron to the O^? ion, it experiences repulsion from the anion due to which the instability of the ion inc

Solution:

Enthalpy in simple terms means chemical energy, the Electron Gain Enthalpy is equal to the energy released or absorbed when an atom gains an electron to form a anion (in gaseous state).

The Negative ion enthalpy is measured when net amount of energy decreases. This happens when atom releases

3.19. On moving down the group, the ionization enthalpy decreases. This is true for B and Al due to the bigger size of Al.

The ionization enthalpy of Ga is unexpectedly higher than Al because Ga contains 10d electrons in inner shell whose shielding is less effective than that of s and p electron

Atomic size: With the increase in atomic size, the number of electron shells increase. Therefore, the force that binds the electrons with the nucleus decreases. The ionization enthalpy thus decreases with the increase in atomic size.

Screening or shielding effect of inner shell electron: With the add

3.17. Electronic configuration of Na and Mg are

Na = 1s² 2s² 2p⁶ 3s¹
Mg = 1s² 2s² 2p⁶ 3s²

First electron in both cases has to be removed from 3s-orbital but the nuclear charge of Na (+ 11) is lower than that of Mg (+ 12) therefore first ionization energy of sodium is

3.16.  (i) In the electronic configuration of Be (1s² 2s²) the outermost electron is present in 2s-orbital while in B (1s² 2s² 2p¹) it is present in 2p-orbital. Since 2s – electrons are more strongly attracted by the nucleus than 2p-electrons, therefore, lesser amount of energy i

3.15. The ionisation enthalpy is for 1 mole atoms.

Therefore, ground state energy of theatoms may be expressed as

E_{ground state} = (– 2.18 x 10^-18 J) x (6.022 x 10²³ mol^-1)

= –1.312 x 10⁶ J mol^-1

Ionisation enthalpy =E_? –E_{ground state}

= 0– (–1.312 x 10⁶mol^-1)

= 1.312 x 10⁶ J mol^-1.

3.14. Significance of the term 'isolated gaseous atom'. The atoms in the gaseous state are far separated in the sense that they do not have any mutual attractive and repulsive interactions. These are therefore regarded as isolated atoms. In this state, the value of ionization enthalpy and elect

3.13. A cation is obtained by removing an electron from the outermost shell. The removal of electron (s) results in decrease of the size of the resulting ion than the parent atom because it has fewer electrons while its nuclearcharge remains the same.

Anions are obtained by addition of electron

3.12.  (a) All of them have 10 electrons each and are isoelectronic in nature.

(b) In isoelectronic species, higher the nuclear charge, smaller will be the atomic or ionic radius.

Al³⁺< Mg²⁺< Na⁺< F^–< O^2-< N^3-