The material making up matter. The rest are called trace elements. Some isotopes are radioactive, they undergo a transformation to gain a stable condition. This transformation is called the half-life of the isotope.
All electrons have the same mass and charge.
These different states of potential energy are called energy levels. Each level is divided into subnets called orbitals. No more than 2 electrons can occupy the same orbital. It is here where atoms come in contact with each other. Any number less than 8 will allow that atom to lose or gain electrons and become stable.