Compounds

Definition of Compounds

A compound is a substance made when two or more different elements chemically combine in a fixed ratio of atoms. The atoms are joined together by chemical bonds to form molecules or giant structures. Compounds have properties that are different from the elements they contain.

For example, water (H₂O) is a compound made from hydrogen and oxygen. Neither hydrogen nor oxygen alone has the same properties as water.

Formation of Compounds

Compounds form when atoms of different elements chemically bond together. This bonding involves atoms either transferring or sharing electrons to achieve a full outer shell, making the compound stable.

There are two main types of chemical bonding that lead to compound formation:

• Ionic bonding: Atoms transfer electrons to form charged ions that attract each other.
• Covalent bonding: Atoms share pairs of electrons to fill their outer shells.

These bonds hold the atoms tightly together, creating the compound’s structure.

Examples of Compounds

Common examples of compounds include:

• Water (H₂O): Two hydrogen atoms covalently bonded to one oxygen atom.
• Carbon dioxide (CO₂): One carbon atom covalently bonded to two oxygen atoms.
• Sodium chloride (NaCl): Sodium and chlorine atoms bonded ionically.

Each compound has a fixed ratio of atoms, for example, water always has 2 hydrogen atoms for every 1 oxygen atom.

For instance, water’s formula H₂O shows the fixed ratio of hydrogen to oxygen atoms. This ratio is always the same in pure water.

Properties of Compounds

Compounds have specific properties that distinguish them from their constituent elements:

• Fixed melting and boiling points: Compounds melt and boil at specific temperatures, which are different from the melting and boiling points of the elements they contain.
• Cannot be separated by physical methods: Unlike mixtures, compounds cannot be separated by simple physical methods such as filtration or evaporation. They require chemical reactions to break them down.
• Distinct chemical properties: Compounds have their own chemical behaviour, which is different from the elements that form them.

For example, sodium chloride (table salt) is a white solid that dissolves in water and tastes salty. Sodium is a reactive metal and chlorine is a poisonous gas, but combined they form a safe compound with very different properties.

The fixed composition and unique properties of compounds make them important in chemistry and everyday life.

Example: Calculate the ratio of atoms in carbon dioxide (CO₂).

The formula CO₂ shows 1 carbon atom and 2 oxygen atoms. So the ratio of carbon to oxygen atoms is 1:2.