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. Correlation of Reactivity with Electron Configurations Write the electron configurations of the halogens. Place dots around symbol to illustrate the number of valence electrons. Top of symbol represents s electrons, other three sides represent the three p orbitals.