2.  Aufbau principle theorizes that an atom is “built up by the addition of electrons, which fill orbitals starting at the lowest available energy orbital before filling higher energy orbitals (for example, 1s before 2s) Figure 1: An aufbau diagram shows how electrons are added to each orbital, beginning with the 1s orbital (bottom left), until no electrons remain (top right).

3.  A rule stating that in a particular set of orbitals of the same energy, the lowest energy configuration for an atom is the one with the maximum number of unpaired electrons allowed by the Pauli exclusion principle  In simpler terms, this means that before any 2 electrons occupy an orbital in a subshell, other orbitals in the same subshell must first each contain 1 electron.

4. Draw the energy-level diagram for phosphorus

5. Draw the energy-level diagram for copper

6. Draw the energy- level diagram for a phosphide ion

7. Draw the energy- level diagram for a oxide ion

8. Drawing Cations TIP: You must draw the energy- level diagram for the corresponding neutral atom first, and then remove the number of electrons (corresponding to the ion charge) from the orbitals with the highest principal quantum number, n.

9. Draw the energy- level diagram for a calcium ion

10. Draw the energy- level diagram for a iron(II) ion