Chemical Bonds & Ionic Bonding

3 min read · free to read

The three types of strong bond

Every strong chemical bond is one of three types, and each is an electrostatic attraction between charged particles

Bond	Particles held together	Found in
Ionic	oppositely charged ions	compounds of a metal with a non-metal
Covalent	atoms sharing pairs of electrons	non-metal elements and compounds of non-metals
Metallic	metal atoms sharing delocalised electrons	metal elements and alloys

Bonding is always explained by electron transfer (ionic) or electron sharing (covalent and metallic), and by the electrostatic forces that result

Ionic bonding

When a metal atom reacts with a non-metal atom, the electrons in the outer shell of the metal atom are transferred to the non-metal atom
The metal atom loses electrons and becomes a positive ion; the non-metal atom gains them and becomes a negative ion
The ions formed have the electronic structure of a noble gas: a full outer shell
The charge on the ion comes from the group number:

Group	Outer electrons	What the atom does	Ion charge
Group 1	1	loses 1	$1+$
Group 2	2	loses 2	$2+$
Group 6	6	gains 2	$2-$
Group 7	7	gains 1	$1-$

Sodium chloride: a sodium atom (2,8,1) gives its one outer electron to a chlorine atom (2,8,7), making $\text{Na}^+$ (2,8) and $\text{Cl}^-$ (2,8,8)
Magnesium oxide: magnesium (2,8,2) gives two electrons to oxygen (2,6), making $\text{Mg}^{2+}$ and $\text{O}^{2-}$
Calcium chloride: one calcium atom gives one electron to each of two chlorine atoms, making $\text{Ca}^{2+}$ and two $\text{Cl}^-$ , so the formula is $\text{CaCl}_2$

Dot and cross diagrams for the formation of sodium chloride and magnesium oxide: outer shells only, the transferred electrons shown as crosses on the negative ion, square brackets and charges on both ions

Ionic compounds

An ionic compound is a giant structure of ions, called a giant ionic lattice: a regular, repeating arrangement
The ions are held by strong electrostatic forces of attraction between oppositely charged ions, acting in all directions. That is what ionic bonding is
Sodium chloride is the only ionic structure you need to know. It can be drawn as a dot and cross diagram, a ball and stick model, or a 2D or 3D space-filling diagram

Sodium chloride lattice drawn three ways: ball and stick, 2D slice showing alternating ions, and a 3D space-filling cube, each labelled with the sodium and chloride ions

Representation	What it shows well	Its limitation
Dot and cross	which electrons move	only one pair of ions, no structure
Ball and stick	the 3D arrangement	ions look small and far apart; the "sticks" are not bonds
2D diagram	the alternating pattern	only one layer of a 3D structure
3D space-filling	ions packed together	only shows the outer ions, hard to see the pattern

The empirical formula of an ionic compound is the simplest ratio of ions: count the ions of each type in a diagram of the structure and simplify. The charges must add up to zero
- Iron(III) oxide contains $\text{Fe}^{3+}$ and $\text{O}^{2-}$ ; two $\text{Fe}^{3+}$ ( $6+$ ) balance three $\text{O}^{2-}$ ( $6-$ ), so it is $\text{Fe}_2\text{O}_3$