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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