Question

Rank the following in order of increasing strength of ionic bonds? `"NaCl", "Mg"_3"N"_2, 2"CaCl"_2, "Na"_3"PO"_4`

Help! I don't understand how to do this question!

Answer 1

`"NaCl < CaCl"_2 < "Na"_3"PO"_4 < "Mg"_3"N"_2`

Explanation:

Here's how I got the order.

The force of attraction `F` between oppositely charged ions follows Coulomb’s law:

`color(blue)(bar(ul(|color(white)(a/a)F = (kq_text(+)q_text(-))/r^2color(white)(a/a)|)))" "`

where

`"q_text(+)` and `q_text(-)` are the charges on the ions
`r` is the distance between the ions
`k` is a proportionality constant

The critical factor is that the force depends on the product of the charges on the ions.

We can make a table of your compounds.

`ulbb("Compound"color(white)(l)q_text(+)color(white)(m)q_text(-)color(white)(m)q_text(+)q_text(-))`
`color(white)(m)"NaCl"color(white)(mmml)1color(white)(mm)1color(white)(mm)1`
`color(white)(m)"Mg"_3"N"_2color(white)(mmll)2color(white)(mm)3color(white)(mm)6`
`color(white)(m)"CaCl"_2color(white)(mmm)2color(white)(mm)1color(white)(mm)2`
`color(white)(m)"Na"_3"PO"_4color(white)(mm)1color(white)(mm)3color(white)(mm)3`

Thus, the order of increasing bond strength is

`"NaCl < CaCl"_2 < "Na"_3"PO"_4 < "Mg"_3"N"_2`