Key concepts in chemistry Study Guide

Atoms are composed of three primary subatomic particles: protons, neutrons, and electrons. Each of these particles has a specific relative charge and relative mass, which are important for understanding atomic structure and chemical behaviour. Protons, located in the nucleus, carry a relative charge of +1 and a relative mass of 1. Neutrons, also in the nucleus, have no charge (a relative charge of 0) and a relative mass of 1. Electrons, which orbit the nucleus in shells, carry a relative charge of -1 and have a negligible relative mass, approximately 1/1836th of a proton or neutron. These relative values simplify calculations and conceptual understanding of atomic properties.

When atoms form covalent bonds, they share pairs of electrons, resulting in the creation of molecules. Molecules are discrete groups of atoms held together by shared electrons. This is distinct from ionic bonding, where ions are formed. Covalent bonding commonly occurs between non-metal atoms, such as in water (H₂O) or oxygen (O₂). Each molecule formed by covalent bonding consists of a specific number and type of atoms joined together through these shared electron pairs.