- Oxygen is a non-metal and beryllium a metal and it takes one of each to form an ionic bond
- Beryllium is in group two on the periodic table, meaning it has two electrons on its valency (outermost) shell
- Oxygen is in group six, meaning that it has six electrons on its valency
- To become stable / unreactive, which is the point all elements are trying to get to, full valency of eight electrons is needed
- Therefore, oxygen and beryllium can form an ionic bond, transferring the two excess electrons from beryllium to oxygen, completing a new shell for oxygen
- This works for beryllium, because the next shell after the two excess electrons have been removed is already complete