1. A molecule is the smallest clique

A molecule (pronounced as more-le-keal) is a close group of atoms. The atoms huddle together because of the strong covalent bond between them.

For example, a water molecule comprises 1 oxygen atom and 2 hydrogen atoms that are held very closely together by covalent bond.

A molecule is a particle consisting of multiple atoms.

2. The atoms within a molecule are all non-metal

Birds of a feather flock together.

And only non-metal atoms flock together to form molecule.

For example, both elements in water molecule, hydrogen and oxygen, are non-metal.

However, when metallic element and non-metallic element combine chemically, they form oppositely charged ions instead of molecules. A key example is sodium chloride, whereby the metallic sodium and non-metallic chlorine exist as ions.

While ions are charged, molecules are electrically neutral with no charge.

A molecule comprises non-metal atoms only.

3. What is a molecule of element?

A molecule of element is formed by atoms of the same element.

For example, in a sample of hydrogen gas, all the atoms are paired up as diatomic molecules. This is why we write the chemical formula of hydrogen gas as H2 to reflect how each molecule has 2 hydrogen atoms.

Likewise, oxygen and chlorine also exist as diatomic molecules.

Element Type of Molecule Chemical Formula
hydrogen diatomic H2
nitrogen diatomic N2
oxygen diatomic O2
fluorine diatomic F2
chlorine diatomic Cl2
bromine diatomic Br2
iodine diatomic I2
phosphorus* polyatomic P4
sulfur* polyatomic S8
List of diatomic molecules. The polyatomic molecules of phosphorus and sulfur are not tested in the O Level.

4. What is a molecule of compound?

A molecule of compound is formed by atoms of two or more elements.

There are many ways that atoms of different elements can combine. When oxygen combines with hydrogen, we get water molecules. But when oxygen combines with carbon, we get carbon dioxide.

The ratio also matters! A carbon dioxide molecule has 2 oxygen bonded to 1 carbon. However, a carbon monoxide molecule has just 1 oxygen bonded to 1 carbon.

5. Molecules are electrically neutral

In this animation, the dot represents the electron of the hydrogen on the left, while the cross represents the electron of the hydrogen on the right. The two electrons are shared to form the diatomic molecule.

A molecule is formed when atoms group together by sharing electrons.

Since no electron is lost or gained, the total number of electrons is equal to the total number of protons in a molecule. With this balance in numbers, a molecule is electrically neutral.

Therefore, covalent substances that are made up of molecules do not conduct electricity in all states.

A molecule is electrically neutral because atoms share electrons, without losing or gaining any additional electron.

6. What is a molecule like under the microscope?

In 2009, scientists in Europe used the scanning electron microscope to look at pentacene molecules. It was the first time a molecule was directly observed.

Each pentacene molecule comprises 5 interconnected rings of carbon atoms that are studded with hydrogen atoms.