Orbitals with the same value of n occupy the same shell. Each shell is divided into subshells. The number of subshells in a given shell is equal to n for that shell. Each subshell is divided into orbitals. Two electrons, with different spins, may occupy one orbital.
Electrons pair up in an orbital only after all orbitals of a subshell contain electrons.
Electron Configurations for the First Two Periods Write electron configurations for the atoms in the first two periods. Can use periodic table position to determine electron configuration. Diamagnetic substances are not affected by a magnetic field because all electrons are paired. Correlation of Reactivity with Electron Configurations Write the electron configurations of the halogens. Elements in a group are chemically similar due to similar valence electron configurations.