Final answer:
Elements form ions by losing or gaining electrons, resulting in a cation or an anion respectively. Oxygen gains two electrons to form an oxide anion, while sodium loses one to form a cation, and aluminum loses two. The changes in electron configuration reflect whether electrons are added or removed.
Step-by-step explanation:
The number of electrons lost or gained by elements when they form ions corresponds to changes in their oxidation states. Oxygen, for instance, has eight electrons in its neutral form, but as an anion (specifically oxide anion O2-), it gains two electrons resulting in a total of ten. Similarly:
- Na (sodium) has an electron configuration of 1s²2s²2p¶3s¹. As a cation (Na+), it loses one electron, resulting in an electron configuration of 1s²2s²2p¶.
- P (phosphorus) starts with an electron configuration of 1s²2s²2p¶3s²3p³. As an anion (P3-), it gains three electrons, leading to a configuration of 1s²2s²2p¶3s²3p¶.
- Al (aluminum) with an initial configuration of 1s²2s²2p¶3s²3p¹ becomes a cation (Al2+) by losing two electrons, changing its configuration to 1s²2s²2p¶3s¹.
When discussing the electron configurations, it's important to note that main group elements lose or gain electrons starting from the last orbital filled, while for transition metals, the last s orbital usually loses electrons before the d orbitals.