• Electrons are found in fixed circular orbits around the

• The orbits correspond to different energy levels in the atom.

• Heat, light or energy can excite electrons to a higher energy level. Energy is released when an excited electron returns to its ground state.

• The maximum electrons which each shell can hold is 2n².

• Up to the first 20 electrons the electron shells fill 2,8,8,2.

• E.g. Sodium (pictured above) would have an electron configuration of 2,8,1 as per this model.

• Electrons behave as waves and occupy 3D ‘orbitals’ around the nucleus.

• There are major energy levels – called shells e.g. 1, 2, 3 and 4.

• Shells contain subshells of similar energy – s,p,d and f. These increase in energy level and the number of orbitals they have.

• Orbitals may be empty or may contain maximum of 2 electrons.

• Electrons always tend to occupy the level of lowest energy.

• E.g. Vandanium (pictured above) would have an electron configuration of 1s²2s²2p⁶3s²3p⁶3d³4s²

^{*Note 4s subshell fills before 3d!}

• Cr and Cu are exceptions and you can learn more about these in this video.