(a) A covalent bond is formed by the overlap of atomic orbitals. The direction of overlapping gives the direction of bond. In ionic bond, the electrostatic field of an ion is non-directional.
Each positive ion is surrounded by a number of anions in any direction depending upon its size and vice-versa. That's why covalent bonds are directional bonds while ionic bonds are non-directional.
(b) In H2O oxygen atom is sp3 hybridise with two lone pairs. The four sp3 hybridised orbitals acquire a tetrahedral geometry with two corners occupied by hydrogen atoms while other two by the lone pairs.
The bond angle is reduced to from due to greater repulsive forces between lp-lp and the molecule thus acquires a V-shape or bent structure (angular structure).
In CO2 molecule, carbon atom is sp-hybridised. The two sp hybrid orbitals are oriented in opposite direction forming an angle of .
That is why H2O molecule has bent structure whereas CO2 molecule is linear.
(c) In ethyne molecule, both the carbona toms are sp hybridised, having two unhybridised orbitals, i.e., and . The two sp hybrid orbitals of both the carbon atoms are oriented in opposite direction forming angle of .
That is why ethyne molecule is linear.
