RLO: Structure of the Atom



Different types of atoms have very different chemical properties and this is mostly due to the arrangement of the electrons orbiting the nucleus. Usually the number of electrons held in orbit around the nucleus of the atom is equal to the number of protons within it – we can think of it as if the positive charge of one proton is able to attract and hold one negatively charged electron to balance it.

The arrangement of the electrons in orbit is highly organised. They are held in a series of concentric orbits, or shells around the nucleus. Each electron orbit or shell can only hold a certain number of electrons. The innermost orbit can hold 2 electrons, the next, 8 and so on. Orbits fill from the innermost outwards.

It is the number of electrons in the outermost orbit that determines much of the atom's chemical properties. Atoms with full outer orbits, such as helium or neon, tend to be inert, whereas those without complete outer shells will react together to donate, collect or share electrons in an attempt to fill, or completely empty,  these orbits.

Electron shells contain 2,8,8,18,18 electrons