Eight. The electrons with the highest energy levels are counted as the valence, or outer, orbitals. There are shells that contain more electrons such as D or F shells that can accommodate for 10 and...
Each orbital can contain a maximum of 2 electrons only different in their spin momentum: +1/2 and -1/2. The 4s orbital is fully 'used' from Ca (no.20) onward: 1s2 2s2 2p6 3s2 3p6 4s2 The 4s2...