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Which of the following has the smallest lattice energy?

a. MgF2

b. CsBr

c. KCl

d. CaO

e. BaS

Solution: Lattice energy is the amount of energy required to separate the ions in a solid crystal lattice into individual gaseous ions. Lattice energy increases with : increased charge of the ions and decreased radius of the ions.

Let's first look at charge remembering that Group1 is usually +1, Group 2 is +2, Group 17 is -1 and group 16 is -2.

a. MgF2 = Mg is 2+ and F is 1-

b.CsBr = Cs is +1 and Br is -1

c. KCl = K is +1 and Cl is -1

d.CaO = Ca is +2 and O is -2

e.BaS = Ba is +2 and S is -2

Since we need the lowest charges for the smallest lattice energy, we can eliminate choices a, d, and e.

For the choices b and c, we need to look for the atoms with the higher atomic radius. Remember that radius increases to the left and down on the Periodic Table.

Choice b is the correct answer choice.



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