In this section there is quite a lot to cover so let’s get stuck in to ionic bonding.
Ionic bonding happens between positive and negative ions which attract each other, kind of like magnets!
When they bind together they form ionic compounds. Ions that bond together are surrounded by oppositely charged ions which attract other ions and form a giant ionic crystal lattice.
The ions in a lattice are very strongly bonded and high temperatures are required if you want to melt the crystal!
The ions are held strongly in position so they cannot move or carry an electric current.
However, if an ionic compound is melted or dissolved in water the ions are then free to move and so the substance can be electrolysed.
We now know that ionic bonding causes these giant lattice structures, great! However there isn’t just one way that ionic bonds can be formed. In fact there are two different ways.
So the first involves metal ions. Sometimes metal ions will lose electrons to become a positively charged ion.
Alternatively non-metal ions may gain electrons to become negatively charged ions.
Metals are early in the periodic table, so generally have one, two or three electrons in their outer shell. It is easier to lose these electrons to form a full shell, than to gain seven, six, or five.
Non-metals are late in the series, generally with six or seven outer shell electrons, so these are more likely to gain electrons to form a complete outer shell. (A full shell has eight electrons remember).
Ionic bonding usually occurs because atoms are attempting to get a more stable electron configuration, usually with a full outer shell of electrons, like noble gases.
This full outer shell is what makes noble gases so unreactive. Because of their stable electron configuration there is no transfer or sharing of electrons required!
If a substance has poor connectivity as a solid but does conduct as a liquid and has a high boiling point, the type of bonding between the molecules is ionic.
Next up we have covalent bonds!
Covalent bonds are responsible for holding atoms together. A covalent bond is formed between non-metal atoms, which combine together by sharing electrons. Covalent compounds have no free electrons and no ions so they don’t conduct electricity.
When a covalent bond forms, the bond electrons are attracted more to the electronegative atom, as this has a greater ability to attract electrons.
Covalently bonded molecules have complete outer shells of electrons, and are neutral, so don’t conduct electricity. In order to boil them, only the weak intermolecular forces must be overcome.
Oxygen is bonded together by a double covalent bond. Each oxygen atom has six outer electrons. Each atom needs to gain two electrons to form a stable outer shell. To do this it needs to form two covalent bonds, sharing two bond pairs with another oxygen atom. This is a double bond.
In metallic bonding, delocalised electrons from the outer shells of metal atoms form a sea of free electrons surrounding positively charged metal ions.
A positively charged lattice of metal ions is surrounded by delocalised electrons which are no longer linked to a single atom. The electrostatic attraction between the electrons and metal ions hold the metal ions together very tightly. The delocalised electrons help us to understand the properties of metals.