19.  Give reasons for the following:-
Electrovalent compounds are soluble in water, insoluble in organic solvents, good conductors of electricity in molten or aq. solution state, have high melting points and undergo electrolytic dissociation on passage of electric current, while covalent compounds are soluble in organic solvents insoluble in water, non-conductors of electricity, have low melting points & undergo ionisation on passage of electric current.

1) Ionic compounds have high melting point and boiling point.

1.Ionic compounds have high boiling point and melting due to presence of strong bond between cations and anions.The negatively charged and positively charged atom associate to form a ordered crystalline structure responsible for its hardness and brittle nature.This association of oppositely charged atom require large amount of to break down and responsible for high boiling point whereas symmetric structure is responsible for high melting point.

2.

2) Ionic compounds conduct electricity in molten state.

Conductivity depends on presence of no. of mobile ions which consist of electron where solid ionic compounds cannot conduct electricity because of the absence no mobile ions (consist of electrons) in the crystal lattice. When the ionic compounds is present in molten state,crystal structure deforms and  they can easily conduct electricity with the mobile ions.

3.

3) Ionic compounds are solid at room temperature and are somewhat hard.

Association of  bunch of little electrical positive and negative charges take place together to form a solid ionic salt crystal in particular direction.When large no. of such association take place, ionic compound formed become hard due to particular arrangement of atoms require high amount of energy to breakdown.

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