Because you can break down every object in the universe into a series of individual atoms, some books refer to them as the "building blocks of matter." All atoms have three different parts: electrons, protons and neutrons. At the center of an atom lies a tiny cluster of protons and neutrons called the nucleus. The electrons orbit around the nucleus in elliptical pathways.
You define an atom by the type of electrical charge it does or does not have. This charge depends on the number of electrons and protons that compose the atom. Protons exude a positive charge while electrons exude a negative charge. An atom with the same number of electrons as protons has no charge at all and is called neutral.
The formation of ions comes completely from manipulating the electrons. Taking away an electron leaves more protons than electrons and creates a positively charged ion called an anion. Adding an electron gives more electrons than protons and yields a negatively charged ion called a cation. By manipulating electrons, scientists can change an element's chemical makeup and allow it to bond with other elements. For example, a positively charged sodium ion combined with a negatively charged chloride ion makes salt.
You can call an ion an atom with an uneven number of protons and electrons, but atoms and ions do have some general differences in their properties. Because ions have a charge, their protons and electrons attract one another; since opposite electrical forces attract. This attraction makes ions much more stable than atoms which have no charge. This difference allows ions to stand alone without the aid of another particle. However, with the exception of noble gases like helium and neon, an atom does not possess the needed stability to exist in its own separate state.