Give reasons for the following :
(i) Covalent bonds are directional bonds while ionic bonds are nondirectional.
(ii) The water molecule has a bent structure whereas carbon dioxide molecule is linear.
(iii) Ethyne molecule is linear.
(i) A covalent bond is formed by the overlapping of the atomic orbitals, therefore, it’s a directional bond. Ionic bond is formed by the transference of electrons and electrostatic field of an ion is there which is non-directional, hence it’s a non-directional bond. Positive ion is surrounded by number of anions in any direction depending upon the size and similarly, negative ion is surrounded by no. of cations in any directional depending upon the size.
(ii) In , oxygen atom is sp3 hybridized and we already know that it is surrounded by two lone pairs and two bonded pairs. There are four sp3 hybrid orbitals which give distorted tetrahedral geometry in which the two corners are occupied by hydrogen atoms and other two by lone pairs. The bond angle is reduced to 104.5° and 109.5°due to greater repulsive forces between 1p-1p and molecules acquire a bent or V-shaped structure. Carbon atom is sp hybridized in and the two sp hybrid orbitals forms linear shape, i.e., an angle of 180° and hence are oriented in opposite direction.
(iii) Both the carbon atoms are sp hybridized in ethyne molecule, and there are two unhybridized orbitals. Hybridized orbitals of both the carbon atoms are directed in opposite directions forming an angle of 180°, and hence, a linear structure is formed.