The second electron shell has an electron capacity of eight electrons. This is because the second electron shell contains four subshells, each of which can hold a maximum of two electrons. The four subshells are labeled s, p, d, and f. The s subshell can hold a maximum of two electrons, the p subshell can hold a maximum of six electrons, the d subshell can hold a maximum of ten electrons, and the f subshell can hold a maximum of fourteen electrons.