Question

the energy required to separate the ions in a nacl crystal lattice into individual na+(g) and cl−(g) ions is known as the lattice energy of nacl(s). as shown in the table below, the lattice energy of nacl(s) is greater than the lattice energy of a similar compound, rbcl(s).
compound lattice energy (kj/mol)
nacl 790
rbcl 686
which of the following best explains why the lattice energy of nacl is greater than the lattice energy of rbcl?
choose 1 answer:
a sodium and chlorine have a smaller electronegativity difference than rubidium and chlorine, so the na−cl bond is less polar than the rb−cl bond.
b na+ contains fewer core electrons than rb+, so the valence electrons in na+ are less shielded from the nucleus than the valence electrons in rb+.
c sodium has a larger first ionization energy than rubidium, so more energy is required to form the na+ ion than to form the rb+ ion.
d na+ has a smaller ionic radius than rb+, so the distance between cation and anion is shorter in nacl than in rbcl.

Explanation:

Lattice energy is related to the distance between ions. Smaller - sized ions result in a shorter distance between cations and anions in the ionic compound, leading to stronger ionic bonds and higher lattice energy. Since the ionic radius of $Na^{+}$ is smaller than that of $Rb^{+}$, the distance between the cation and anion is shorter in $NaCl$ than in $RbCl$, which explains why the lattice energy of $NaCl$ is greater.

Answer:

D. $Na^{+}$ has a smaller ionic radius than $Rb^{+}$, so the distance between cation and anion is shorter in $NaCl$ than in $RbCl$