Molécules et composés

In nature, pure substances are classified as either elements that cannot be broken down into simpler substances or compounds made up of two or more elements combined in fixed ratios.

Depending on the type of atom, elements exist either as single atoms or as molecular elements, while compounds can be either molecular or ionic.

Single atoms are the simplest units of atomic elements, such as helium, neon, and krypton.

Molecular elements, on the other hand, contain two or more identical atoms bonded together, forming a molecule as the base unit, like hydrogen or sulfur.

Molecular compounds form when atoms of two or more nonmetallic elements combine by sharing valence electrons through covalent bonds.

For example, water forms through the covalent bonding of one oxygen atom and two hydrogen atoms.

Ionic compounds form when ions of metallic elements combine with ions of one or more nonmetallic elements through electrostatic forces.

For example, in table salt, sodium metal atoms lose their valence electrons and form positively charged cations, while chloride nonmetal atoms gain electrons and form negatively charged anions.