Question

Choose the compound below that should have the highest melting point according to the ionic bonding model. Choose the compound below that should have the highest melting point according to the ionic bonding model. MgO LiF AlN RbF CaS

Answer 1

Answer:

AlN has highest melting point among given.

Explanation:

As per ionic model, ionic compounds are held together by electrostatic force. The ionic compound having strong electrostatic force will have high melting point.

Electrostatic force is proportional to charge and size of constituent ions.

$F=k \frac{q_+\times q_-}{r^2}$

In case of MgO

Charge on Mg = +2

Charge on O = -2

$F=-k \frac{(+2)\times (--2)}{r^2}=\frac{4k}{r^2}$

In case of LiF

Charge on Li = +1

Charge on F = -1

$F=-k \frac{(+1)\times (-1)}{r^2}=\frac{1k}{r^2}$

In case of AlN

Charge on Al = +3

Charge on N = -3

$F=-k \frac{(+3)\times (-3)}{r^2}=\frac{9k}{r^2}$

In case of RbF

Charge on Rb = +1

Charge on F = -1

$F=-k \frac{(+1)\times (-1)}{r^2}=\frac{1k}{r^2}$

In case of CaS

Charge on Ca = +2

Charge on S = -2

$F=-k \frac{(+2)\times (-2)}{r^2}=\frac{4k}{r^2}$

As magnitude of electrostatic force is highest in AlN, therefor, it has highest melting point.