Question

Choose the compound below that should have the highest melting point according to the ionic bonding model. A) AlN B) MgO C) NaF D) CaS E) RbI

Answer 1

Answer:

The correct answer is C.

Explanation:

The compound with the highest melting point according to the ion bond model is the one with the greatest electronegativity difference, since the ion bond is stronger and therefore more difficult to break.

The electronegativity difference is calculated as the electronegativity difference of the atoms of the molecule.

AlN: Al (1,61) and N (3,04) so the difference gives 1,43.

MgO: Mg (1,31) and O (3,44) so the difference gives 2,13.

NaF: Na (0,93) and F (3,98) so the difference gives 3,05.

CaS: Ca (1) and S (2,58) so the difference is 1,58.

RbI: Rb (0.82) and I (2.66) so the difference is 1.84.

Analyzing the different cases, we can conclude that the molecule that presents the greatest difference in electronegativity is NaF, so it will have a higher boiling point due to the attraction force between its atoms.

Have a nice day!

Answer 2

Answer:

C

Explanation:

Strength of ionic bonds depends on the relative sizes of the ions, the smaller the ions, the more efficiently they arrange themselves in a neat crystal lattice. NaF is the strongest purely ionic crystal in the list. Remember that the question emphasised the ionic bonding model. Though AlN is composed of small ions, but the compound has a high degree of covalent character and cannot be considered based purely on an ionic model as spelt out in te question.