The outermost shell of an iron atom contains two electrons. This number can be found from the electron configuration for iron, written as 1s2 2s2p6 3s2p6d6 4s2. The outermost shell is the fourth energy level, which contains two electrons in the s-orbital.
An atom of iron contains a total of 26 electrons, with two in its first shell, eight in its second shell and 14 in its third shell. Electron shells are also known as energy levels. The electrons in each shell are divided into sub-shells, or energy orbitals, which are represented by the letters s, p, d, f and g. Each shell and sub-shell has a maximum limit on the number of electrons it can contain.