Key concepts in chemistry Study Guide

Atoms, in their natural, unreacted state, are electrically neutral. This means they carry no net electrical charge. This neutrality arises because atoms contain an equal number of positively charged protons and negatively charged electrons. Protons are located within the atom's nucleus and each carries a charge of +1. Electrons orbit the nucleus and each carries a charge of -1. For the atom to be neutral, the total positive charge from the protons must exactly balance the total negative charge from the electrons. Therefore, if there are 'X' protons, there must be 'X' electrons to ensure the overall charge is zero. The number of neutrons in an atom can vary, creating isotopes, but neutrons have no electrical charge and thus do not affect the overall charge balance.

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.