Electron Shells

An electron can be considered to be a cloud of negative charge. Electrons in different shells have different energy levels. The shells are given a principal quantum number n where n = 1,2,3,4,5,6 and 7. The shell with the lowest energy is shell n = 1 and is closest to the nucleus.
The maximum number of electrons is given by 2n².The main energy levels are sub-divided into sub-shells called s,p,d and f sub-shells. The s,p,d, and f subshells consist of s, p, d and f atomic orbitals.

An orbital is a region in space where there is a high probability(90-95%) of finding an electron.

The shape of an orbital represents a region in space where there is a 95% probability of finding an electron. Each orbital can hold a maximum of two electrons.
The first main energy level consists of a single s orbital. The next energy level has one s and three p orbitals. The next level has one s, three p and five d orbitals. The next level has seven f orbitals in addition to these.1s
2s
2p^x 2p^y 2p^z
3s
3p^x 3p^y 3p^z
3d^xy 3d^yz 3d^xz 3d^{x2–y 2} 3d ^z2
4s ...