Question

Question 1:

Specify which compound in each of the following pairs of ionic compounds should have the higher lattice energy. For each, identify the major reason for the difference.

(a) AlN or CaO

(b) NaF or CsF

(c) MgCl2 or MgF2

Higher lattice energy:

	CaO
	AlN

	CsF
	NaF

	MgF2
	MgCl2

Reason:

	Higher charge on Al and N ions
	Higher charge on Ca and O ions
	Smaller distance between Al and N
	Smaller distance between Ca and O

	Higher charge on Na and F ions
	Higher charge on Cs and F ions
	Smaller distance between Na and F
	Smaller distance between Cs and F

	Higher charge on Mg and Cl ions
	Higher charge on Mg and F ions
	Smaller distance between Mg and Cl
	Smaller distance between Mg and F

Question 2:

Be sure to answer all parts.

Four atoms are arbitrarily labeled D, E, F, and G.

Their electronegativities

are as follows:

D = 3.8,

E = 3.3,

F = 2.8,

and

G = 1.3.

If the atoms of these elements form the molecules DE, DG, EG, and DF, how would you arrange these molecules in order of increasing covalent bond character?

Place the symbols DE, DG, EG, and DF in the proper sequence, with the most covalent bond on the right.

Answer 1

Lattice energy is directly proportional to charges

Lattice energy is inversely proportional to distance

From Born Lande equation

Question : 1

AlN ----> Higher charge on Al and N ions

because the ions involved are 3+/3-, while those involved in CaO are 2+/2-.

NaF ---> Smaller distance between Na and F

Both Na and Cs are + ions, but Na⁺ is smaller than Cs⁺ and so will have a stronger force of attraction for F^- and

less distance between the ions

MgF₂ ---> Smaller distance between Mg and F

Both F and Cl are - ions, but F^- is smaller than Cl^- and so will have a stronger force of attraction for Mg²⁺ and less

distance between them

Question :2

More is the difference between the electronegativities of atoms ---> more the ionic character and less the covalent

character

So here , ascending order of covalent character is

DG < EG < DF < DE