Key concepts in chemistry Study Guide

Atoms are the fundamental building blocks of matter, composed of subatomic particles: protons, neutrons, and electrons. The vast majority of an atom's mass is concentrated within its central region, known as the nucleus. This nucleus contains both protons and neutrons, which are significantly more massive than electrons. Electrons, though occupying the largest volume of the atom, contribute very little to its overall mass due to their negligible individual masses. This characteristic distribution of mass is crucial for understanding atomic structure and behavior.

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.