Give reason for the following.
a) Covalent bonds are directional bonds while ionic bonds are non-directional.
b) Wate molecules has bent whereas carbon dioxide molecule is linear.
c) Ethyne molecule is linear.

Answer

a

Explanation

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 `H_(2)O` oxygen atom is `sp^(3)` hybridised with two lone pairs. The four `sp^(3)` 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 `104.5^(@)` from `109.5^(@)` due to greater repulsive forces between Ip-Ip and the molecule thus acquires a V-shape or bent structure (angular structure )

In `CO_(2)` molecule, carbon atom in sp-hybridised. The two sp hybrid orbitals are oriented in opposite direction forming an angle of `180^(@)`.

Thats, why `H_(2)O` molecule has bent structure whereas `CO_(2)` molecule is linear.
c) In ethyne molecule, both the carbon atoms are sp hybridised, having two unhybridised orbitals, i.e, `2p_(x)` and `2p_(y)`. The two sp hybrid orbitals of both the carbon atoms are oriented in opposite direction froming an angle of `180^(@)`
`H-Cunderset(2pi-bond)overset(sigma)-=C-H`
That's why ethyne molecule is linear.