(i) Valence shell electronic configuration of oxygen atom is:2s² 2p²; 2p¹_y,2p¹₂;

(ii) When the half filled P_z orbitals of two oxygen atoms overlap along the z-axis a (J covalent bond is formed between them. Other two half filled P_y orbitals of two oxygen atoms overlap laterally to form a rt-covalent bond between the oxygen atoms.
(iii) Thus in oxygen molecule, two oxygen atoms are connected by two covalent bonds (double bond). The other two pair of electrons present in the 2s and Zp_x , orbital do not involve in bonding and remains as lone pair on the respective oxygen atoms.

(i) Cations having ns⁶nd⁶nd¹⁰ configuration show greater polarising power than the cations with ns²np⁶ configuration. Hence they show greater covalent character.
(ii) CuCI is more covalen"t than NaCI. As compared to Na⁺ (1.13Å), Cu+ (0.6Å) is small and has 3s²3p⁶3d¹⁰ configuration.
(iii) Electronic configuration of Cu⁺: [Ar] 3d¹⁰
Electronic configuration of Na⁺ [He] 2s²p⁶
So CuCI is more covalent than NaCl

(i) The extent of ionic character in a covalent bond can be related to the electronegativity difference of the bonded atoms.
(ii) In a typical polar molecule A^ઠ- - B^ઠ++, the electronegativity difference (X_A - X_B) can be used to predict the percentage of the ionic character as follows:
(iii) If the electronegativity difference X_A - X_B is equal to 1.7, then the bond A - B has 50% ionic character.
(iv) If it is greater than 1.7, then the bond A - B has more than 50% ionic character.
(v) If it is lesser than 1.7, then the bond A - B has less than 50% ionic character.

(i) In the case of polyatomic molecules with two or more same bond types, the arithmetic mean of the bond energy value of the same type of bonds is considered as average bond enthalpy.
(ii) For e.g., in water, there are two OH bonds present and the energy needed to break them are not same
(iii) \({ H }_{ 2 }O_{ (g) }\longrightarrow H\left( g \right) +OH\left( g \right) \Delta { H }_{ 1 }=502kJ{ mol }^{ -1 }\)
\(OH(g)\longrightarrow H(g)+O(g)\Delta H=427KJmol\)
The average bond enthalpy of OH bond in water
=\(\cfrac { 502+427 }{ 2 } =464.5KJmol^{ -1 }\)