Home : Structures : Covalent Bonds
In the last lesson we saw that atoms can lose or gain electrons to form ionic bonds. However, there is another way in which atoms can use their electrons to join together to form molecules.
Most atoms want to get eight electrons in their outside shell ... but hydrogen is different: it wants to get only two electrons in its outside shell.
Carbon is like other atoms - it wants eight atoms in its outside shell - so it can either give four electrons away or gain another four to make eight.
a hydrogen atom
a carbon atom
Ionic bonding is when atoms gain or lose . Most atoms want electrons in their outside shells but a hydrogen atom wants only electrons.
Carbon is an atom with a total of electrons. This means that it has electrons in its outside shell.
Carbon and hydrogen atoms can join together to form methane - however, in this molecule, the atoms share their electrons. When atoms share electrons to join together it is called covalent bonding.
The diagram shows how four hydrogen atoms can join to one carbon atom to form methane (CH4). If you count the number of electrons in the outside shell of the carbon atom - there are eight of them. However, by sharing their electrons, the hydrogen atoms have two electrons in their outside shells.
So, by sharing electrons, both the hydrogen and carbon atoms are happy.