Each hydrogen molecule comprises two hydrogen atoms joined by a covalent bond.

The two atoms are so close together that their outer electron shells overlap.

One electron from the outer shell of each atom is shared between the two atoms.

Each electron is attracted to the nuclei of both atoms, forming a covalent bond.

The electron from one atom is shown here as a dot and the other is shown as a cross.

This is called a dot-cross diagram.

A covalent bond is a shared pair of electrons. It is often shown as a line.

One shared pair of electrons is called a single covalent bond.

When atoms are combined by covalent bonds they form molecules.

This is a model of a molecule of ammonia, NH 3.

Each hydrogen atom is bonded to the nitrogen atom by a single covalent bond.

Each hydrogen atom shares its electron with the nitrogen atom.

The nitrogen atom shares three electrons from its outer shell.

Pairs of electrons that form a bond are called bonding pairs. There are three Bonding pairs here.

Nitrogen is in Group 5, so there are five electrons in its outer shell.

Three of these are bonding electrons, leaving two electrons that are not involved in bonding.

A pair of non-bonding electrons is called a lone pair.

A water molecule contains two hydrogen atoms and one oxygen atom.

Each hydrogen atom is bonded to the oxygen atom by a single covalent bond.

Each hydrogen atom shares its electron with the oxygen atom.

The oxygen atom shares two electrons from its outer shell.

There are two bonding pairs of electrons.

Oxygen is in Group 6, so there are six electrons in its outer shell.

Two of these are bonding electrons, leaving four electrons that are not involved In bonding.

These four electrons from two lone pairs of electrons.

An oxygen molecule contains two oxygen atoms. How many bonds does it have?

There are two covalent bonds between the oxygen atoms, called a double bond.

Each oxygen atom shares two electrons from its outer shell.

There are two bonding pairs of electrons, forming a double bond.

Each oxygen atom has two bonding electrons and four non-bonding electrons.

The non-bonding electrons from two lone Pairs of electrons around each oxygen atom.

A nitrogen molecule contains two nitrogen atoms. How many bonds does it have?

There are three covalent bonds between the nitrogen atoms, called a triple bond.

Each nitrogen atom shares three electrons from its outer shell.

There are three bonding pairs of electrons, forming a triple bond.

Nitrogen is in Group 5, so it has five electrons in its outer shell.

Each nitrogen atom has three bonding electrons and two non-bonding electrons.

These electrons from a lone pair of electrons around each nitrogen atom.

Hydrogen can form one covalent bond.

The number of bonds that most other non-metals can from is 8 minus the Group number.

Carbon is in Group 4. It forms 8 – 4 = 4 covalent bonds.

Nitrogen is in Group 5. It forms 8 – 5 = 3 covalent bonds.

Oxygen is in group 6. It forms 8 – 6 = 2 covalent bonds.

Chlorine is in group 7. It forms 8 – 7 = 1 covalent bonds.

Neon is in group 0. It has a full outer shell and does not form covalent bonds.

Sometimes one of the atoms contributes both of the bonding electrons.

When this happens, a dative covalent bond forms.

This happens in carbon monoxide, CO.

The carbon atom contributes two bonding electrons, leaving a lone pair of electrons.

The oxygen atom contributes two bonding electrons, forming two covalent bonds.

Two electrons in the outer shell of the oxygen atom form a lone pair of electrons.

The last two outer electrons in the outer shell of the oxygen atom form a dative covalent bond.

The ordinary covalent bonds are shown with a line as usual.

The dative covalent bond is shown with an arrow instead of a line.

The arrow points away from the atom that contributes both bonding electrons.