Question

Compound Lattice Energy (kJ/mol) Compound Lattice Energy (kJ/mol) LiF 1030 NaCl 788 LiCl 834 MgCl2 2326 LiI 730 AlCl3 5376 Lattice Energy 1 Lattice Energy 2 For the lattice energies given above … in Lattice Energy 1, explain why LiF has a greater lattice energy than LiI in Lattice Energy 2, explain why NaCl has a smaller lattice energy than AlCl3

Answer 1

LiF has a greater lattice energy than LiI due to the greater charge and smaller size of the fluoride ions. NaCl has a smaller lattice energy than AlCl3 due to the lower charge and similar size of the sodium ions compared to aluminum ions.

Step-by-step explanation:

The lattice energy of an ionic compound depends on several factors, including the charges of the ions and the distance between them. In the case of LiF and LiI, LiF has a greater lattice energy because fluoride ions (F¯) have a higher charge (-1) compared to iodide ions (I¯) (-1). Additionally, F¯ ions are smaller in size compared to I¯ ions, resulting in a shorter interionic distance, which increases the lattice energy of LiF.

Similarly, in Lattice Energy 2, NaCl has a smaller lattice energy compared to AlCl3 due to the difference in the charges and sizes of the ions. NaCl has a smaller lattice energy because sodium ions (Na+) have a lower charge (+1) compared to aluminum ions (Al3+), and the size of the chloride ions (Cl¯) is similar to that of the aluminum ions, resulting in a shorter interionic distance for NaCl compared to AlCl3.

Answer 2

The lattice energy decreases down the group and increases across the period, therefore, the lattice energy of LiF > lattice energy of LiI, and the lattice energy of NaCl < the lattice energy of AlCl₃

Step-by-step explanation:

The given parameters are;

Compound
`{}` Lattice Energy (kJ/mol)

LiF
`{}` 1030

NaCl
`{}` 788

MgCl₂
`{}` 2326

LiI
`{}` 730

AlCl₃
`{}` 5376

Lattice is the energy that must be added in order to split one mole of a ionic solid compound into gaseous ions

Given that the force of attraction between charges is inversely proportional to the square of the distance separating the charges, we have that as the atomic radius increases progressively down the group, the lattice energy decreases, therefore, LiF which has a shorter inter nuclear distance than LiI due to fluorine, F, being higher up on the periodic table than iodine, I, has a greater lattice energy than LiI

Similarly, given that the atomic radius decreases across the period, and that sodium, Na, comes before aluminum, Al, as we move across period 3, of the periodic table, the inter nuclear distance between atoms of in NaCl is larger than the internuclear distances between the atoms of AlCl₃, as well as the presence of more chlorine atoms in AlCl₃ than in NaCl, the lattice energy of NaCl is smaller than the lattice energy of AlCl₃.