Describing ionic bonding: NaCl, MgO and CaF₂

By the end of this lesson

By the end you can describe the ionic bonding in sodium chloride, magnesium oxide and calcium fluoride: which electrons move, the ions formed, their ratio, and what holds them together.

What they ask

"Describe the bonding in magnesium oxide."
"Draw a dot-and-cross diagram for calcium fluoride, showing outer electrons only."
"Explain why the formula of calcium fluoride is $\text{CaF}_2$ ."

Same question in three outfits. One method answers all of them.

The method

Write the electron arrangement of each atom.
Work out how many electrons the metal atom loses, and the non-metal atom gains, to reach a noble-gas arrangement.
Balance the electrons lost with the electrons gained: this sets the ratio of ions, and so the formula.
Write each ion with its charge and arrangement. In a diagram: square brackets, the charge at the top right, crosses for the metal's electrons and dots for the non-metal's.
Name the bond: electrostatic attraction between the oppositely charged ions, acting in all directions in a giant lattice.

You've already met the simplest case, NaCl: one electron lost, one gained, ratio 1 : 1.

Look at the anions. O²⁻ holds both of magnesium's electrons (two crosses); each F⁻ holds one of calcium's (one cross each).

Worked example: Magnesium oxide

Describe the ionic bonding in magnesium oxide, $\text{MgO}$ .

Have a go first?

Quick check

CalculateQuestion 1 · Recall

Multiple choiceQuestion 2 · Recall

Answer the 2 questions above to continue.