Matter is made up of very tiny particles (building blocks) known as atoms, molecules or ions. An atom is the smallest electrically neutral particle of an element that takes part in a chemical reaction.
A molecule is the smallest electrically neutral particle of a compound or an element that is formed by the combination of atoms in a whole number ratio and can exist on its own.
In a molecule of an element, the combining atoms are the same (for example; the oxygen molecule, ) In a molecule of a compound, different atoms combine (for example the hydrogen chloride molecule, ) A molecule retains the properties of that element or compound it contains.
An ion is an atom or a group of chemically combined atoms that has either lost one or more electrons, making it positively charged (a cation), or gained one or more electrons, making it negatively charged (an anion).
The structure of an atom
An atom is spherical in shape and has a small region in the center called the nucleus. The atom contains protons and neutrons, and electrons as fundamental particles. The protons and neutrons are concentrated in a very small nucleus in the center of the atom while the electrons are all outside the nucleus in the energy levels and are constantly rotating around the nucleus. The number of electrons in the energy levels (negative charges) is equal to the number of all protons in the nucleus (positive charges) hence an atom is neutral.
The energy level closest to the nucleus is called the first energy level or the K energy level. The second closest energy level to the nucleus is the second energy level or the L energy level. This is followed by the third energy level or the M energy level. So, the energy levels are named 1st, 2nd, 3rd, 4th, and so on or K, L, M, N and so on from the energy level closest to the nucleus outwards.