How many core electrons are in a chlorine atom?

So it has 2 core and 4 valence electrons. Chlorine 2,8,7 (1s1 2s2 2p6 3s2 3p5) has 17 electrons, in in group 7 but has a valency of 1. However it is classed as having 10 core electrons and 7 valence electrons. read more

So 12 core and 1 valence Carbon 2,4 (1s1 2s2 2p2) has 6 electrons, is in group 4 and a valency of 4. So it has 2 core and 4 valence electrons Chlorine 2,8,7 (1s1 2s2 2p6 3s2 3p5) has 17 electrons, in in group 7 but has a valency of 1. However it is classed as having 10 core electrons and 7 valence electrons. read more