(a) Explain why carbon can only form covalent bonds and not $C^{4+}$ cations or $C^{4-}$ anions. Also, state reasons to explain why covalent compounds.
(i) Are poor conductors of electricity.
(ii) Have low melting and boiling points.
(b) Draw the structural formula of benzene, $C_6{H}_6$.

                                        (OR)

What are isomers?
(b) Two compounds have the same molecular formula $C_3{H}_{6}O.$ Identify the name of the compounds and write their structural formula.
(c) Mentions the steps involved in bringing the following conversion.
(i) Ethanol to ethene
(ii) Propanol to propanoic acid
 

(a) Carbon has a tetravalency but can't gain or lose electrons because; 

 (1) If it gains electrons, it will be $C^{4-}$ with a negative charge. It is very difficult for 4 protons to hold on to 8 electrons, and it becomes unstable. 

(2) If it loses 4 electrons ad forms$C^{4+}$, it requires a lot of energy to lose it, which it can't afford, and again becomes unstable.
(i) Covalent bonds are formed by sharing electrons and sharing them as molecules, so the transfer of electrons takes place. Since ions are responsible for conducting electricity and they do not have free ions, they are bad conductors of electricity. e.g. $\left(C{H}_4\right)$

(ii) Since the molecule of 2 different element share electrons, they have weak forces of attraction and weak electrostatic forces, due to which their bond can be broken easily. The bonds are strong within the molecule, but ionic bonds are weak, making them have low melting and boiling points. E.g. Naphthalene has a melting point of about 80° 𝐶.

(b) The structural formula of benzene $C_6{H}_6$.

                                                    (OR)

(a) A compound having the same molecular formula but different physical and chemical properties are called an isomer, and this phenomenon is known as isomerism.
(b) Acetone IUPAC name: propanone, $\left(C{H}_{3}COC{H}_3\right)$and propanal $\left(C{H}_{3}C{H}_{2}CHO\right)$ are two compounds that have the same molecular formula $C_3{H}_{6}O.$ The name of these compounds and their structural formula are;

(c) Conversion of;
(i) Ethanol to ethene:
Heating ethanol with an excess of concentrated sulphuric acid at about ${170}^{\circ }C$ gives ethene, the process of the dehydration process. The chemical reaction follows;

(ii) Propanol to propanoic acid In the chemical reaction of the conversion of propanol to propanoic acid, propanol gets oxidized to propanoic acid in the presence of alkaline potassium permanganate. The chemical reaction is as follows;