Ionic Compounds
Ionic compounds are formed by metal (gp 1-3) and non-metal (gp 4-7)
Properties
-High melting point and boiling point ( considered as one point in exam ).
-Soluble in water.
-Conduct electricity in molten (hot liquid ) and in aqueous states
Note: does not conduct electricity in solid states!!!
Metal conduct electricity in molten and in solid states.
Covalent Compounds
Covalent compounds are formed only by non-metal elements.
Properties
-Low melting and boiling points
-Soluble in organic solvents
-Poor conductor of electricity
EXCEPTION: HCl is a good conductor of electricity.
Reason: When HCl dissolves in water, it dissociates to produce H+ and Cl-. It is the free mobile ions that conduct electricity! (Typical MCQ Question! )
(Typical Structure Question)
Question: Both sodium chloride and chlorine gas are compounds of chlorine; sodium chloride exist as a solid while chlorine exist as a gas. Explain why.
Answer:
Sodium chloride is an ionic compound [ 1mark ]. A large amount of energy is needed to overcome the strong electrostatic forces of attraction between oppositely charged ions [ 1mark] . Hence high melting point. This is why it exist as a solid at room
temperature.
Chlorine gas is a covalent substance [ 1mark]. A small amount of energy is needed to overcome the weak intermolecular force of attraction between the molecules [ 1mark]. Hence low melting point. This is why it exist as a gas at room temperature.
Note: Although 'Hence high melting point. This is why it exist as a solid at room temperature.' has no mark allocation, this phrase has to be included for the completeness of answer!
