Electron configuration practice
Use the periodic table to write the configuration, then build the orbital diagram.
Ion rules
Cations lose electrons from the highest energy level first: np before ns, and ns before (n−1)d. So 4s empties before 3d.
Anions add electrons to the next open orbitals, usually reaching a noble gas configuration.
p-block metals like Tl, Sn, Pb and Bi form two common ions. One loses only the np electrons (Tl⁺, Sn²⁺, Pb²⁺, Bi³⁺). The other loses the np and ns electrons (Tl³⁺, Sn⁴⁺, Pb⁴⁺, Bi⁵⁺).
Silver is an exception: Ag is [Kr] 5s¹ 4d¹⁰, and Ag⁺ is [Kr] 4d¹⁰.
1. Full configuration
Type each subshell with its electron count, like 1s2 2s2 2p6.
2. Noble gas abbreviation
Replace the inner electrons with the noble gas at the end of the previous period, like [Ne] 3s2 3p4.
3. Orbital diagram
Click a box to cycle through empty, ↑, ↓, ↑↓ and ↑↑. Energy increases going up.
4. Unpaired electrons
How many electrons are alone in their orbital?