How do atoms combine to form compounds?

Atoms combine to form compounds through chemical reactions, specifically by sharing or transferring electrons in a process called bonding.

Atoms are the basic units of matter and the defining structure of elements. They contain protons, neutrons, and electrons. The protons and neutrons are located in the nucleus at the centre of the atom, while the electrons orbit in shells around the nucleus. The outermost shell of an atom is known as the valence shell, and the electrons in this shell are called valence electrons. These valence electrons play a key role in the formation of compounds.

Compounds are formed when two or more atoms combine through chemical reactions. This happens when the valence electrons of one atom interact with the valence electrons of another atom. There are two main types of chemical bonds that atoms can form to create compounds: covalent bonds and ionic bonds.

In a covalent bond, atoms share one or more pairs of valence electrons. This type of bond usually occurs between non-metal atoms. For example, in a water molecule (H2O), the oxygen atom shares a pair of electrons with each of the two hydrogen atoms.

In an ionic bond, one atom transfers one or more of its valence electrons to another atom. This results in the formation of ions, which are atoms or groups of atoms with a net electric charge. Ionic bonds typically occur between metal and non-metal atoms. For example, in sodium chloride (NaCl), the sodium atom transfers one of its valence electrons to the chlorine atom, forming positively charged sodium ions and negatively charged chloride ions.

In both types of bonds, the atoms achieve a stable electron configuration, usually with a full outer shell of electrons. This is often referred to as the 'octet rule', as atoms tend to be most stable when their outer shell is full with eight electrons. The formation of compounds through chemical bonding is a fundamental concept in chemistry, underpinning the structure and properties of all matter.