Question

(A): Explain the following :

(i) Electrovalent compounds conduct electricity in molten or aqueous state.

(ii) Electrovalent compounds have a high melting point and boiling point while covalent compounds have low melting and boiling points.

(iii) Atoms combine by transfer and sharing of electrons (s).

(B): Explain that the formation of magnesium chloride is a redox reaction.

Answer 1

(A) (i) Electrovalent compounds in the solid state do not conduct electricity because movement of ions in the solid state is not possible due to their rigid structure. But these compounds conduct electricity in the molten state. This is possible in the molten state since the electrostatic forces of attraction between the oppositely charged ions become weak. Thus, the ions move freely and conduct electricity.

(ii) The atoms of covalent compounds are bound tightly to each other in stable molecules, but the molecules are generally not very strongly attracted to other molecules in the compound. On the other hand, the atoms (ions) in electrovalent compounds show strong attractions to other ions in their vicinity. This generally leads to low melting points for covalent solids, and high melting points for electrovalent solids.

(iii)Covalent bond is the bond formed in which two atoms share a pair of electrons and form molecules. The bond that results whenever unequal sharing occurs is called polar covalent bond while equal sharing of electrons is called non polar covalent bond.

(B)

Mg(s)+Cl2(g)→MgCl2(s)

Explanation:

The metal loses electrons, and in forming Mg2+it loses 2 electrons and is oxidized:

$Mg\left(s\right)⟶M{g}^{+2}+2e^{-1}$ ------------- (i)

And on the other hand chlorine is reduced to chloride ion by accepting electrons:

$C{l}_2\left(g\right)+2e^{-1}⟶2C{l}^{-}$ ----------- (ii)

And add both (i) and (ii), cancelled out the e-s on both side.

$Mg\left(s\right)+C{l}_2\left(g\right)⟶MgC{l}_2\left(s\right)$

Both charge and mass are balanced, as required.