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Common Small Molecules

There are certain small molecules that you should be familiar with. They are shown below. For each one, you should learn the name, molecular formula and displayed formula.

Water

Molecular formula:

H2O

Displayed formula:

Displayed formula of a water molecule. One oxygen atom is bonded to two hydrogen atoms. The bonds are shown as lines. The atoms are represented by their chemical symbols (O and H).

Displayed formula of a water molecule.

Hydrogen peroxide

Molecular formula:

H2O2

Displayed formula:

Displayed formula of a hydrogen peroxide molecule. A hydrogen atom is bonded to an oxygen atom, which is bonded to another oxygen atom, which is bonded to a hydrogen atom.

Displayed formula of a hydrogen peroxide molecule.

Ammonia

Molecular formula:

NH3

Displayed formula:

Displayed formula of an ammonia molecule. A nitrogen atom is bonded to three hydrogen atoms.

Displayed formula of an ammonia molecule.

Carbon dioxide

Molecular formula:

CO2

Displayed formula:

Displayed formula of a carbon dioxide molecule. A carbon atom is bonded to two oxygen atoms. Both of the bonds are double covalent bonds.

Displayed formula of a carbon dioxide molecule.

Methane

Molecular formula:

CH4

Displayed formula:

There is a carbon atom in the centre. It is bonded to four hydrogen atoms.

Displayed formula of a methane molecule.

Hydrogen chloride

Molecular formula:

HCl

Displayed formula:

The displayed formula of hydrogen chloride. A single hydrogen atom (H) is bonded to a single chlorine atom (Cl).

Displayed formula of hydrogen chloride.

Oxygen

Molecular formula:

O2

Displayed formula:

The displayed formula of an oxygen molecule. There are two oxygen atoms, each represented by the letter O. They are joined by a pair of lines (one on top of the other) representing a double covalent bond.

Displayed formula of oxygen molecule.

Nitrogen

Molecular formula:

N2

Displayed formula:

The displayed formula of nitrogen. Two nitrogen atoms are joined by a triple bond.

Displayed formula of nitrogen.

Hydrogen

Molecular formula:

H2

Displayed formula:

The displayed formula of hydrogen. Two hydrogen atoms are joined by a single bond.

Displayed formula of hydrogen.

Note that in all of the molecules above, every atom has the number of bonds we would expect it to have based on the group number of its element. All of the carbon atoms have four bonds, the nitrogen atoms have three bonds, the oxygen atoms have two bonds, the hydrogen atoms have one bond, and the chlorine atoms have one bond.

Also, note that some of the molecules have the same name as the element they are made of. For example, an oxygen molecule is made of oxygen atoms. Usually if a molecule is made up of atoms that are all the same element, then the molecule is named after the element.

This means that there can be multiple different particles that have the same name. For example, an O atom is called 'oxygen' and an O2 molecule is also called 'oxygen'.

Flashcards

Flashcards help you memorise information quickly. Copy each question onto its own flashcard and then write the answer on the other side. Testing yourself on these regularly will enable you to learn much more quickly than just reading and making notes.

1/9

What is the molecular formula of water?

2/9

What is the molecular formula of hydrogen peroxide?

3/9

What is the molecular formula of ammonia?

4/9

What is the molecular formula of carbon dioxide?

5/9

What is the molecular formula of methane?

6/9

What is the molecular formula of hydrogen chloride?

7/9

What is the molecular formula of oxygen?

8/9

What is the molecular formula of nitrogen?

9/9

What is the molecular formula of hydrogen?

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