How many core electrons are in Iodine?

##46##

Iodine, ##"I"##, is located in period 5, group 17 of the , and has an equal to ##53##.

That means that a neutral iodine atom will have a total of ##53## electrons surrounding its nucleus.

Now, out of these ##53## electrons, some are considered core electrons and some areconsidered .

##n_"total" = n_"valence" + n_"core"##

But how would you distinguish between the two types of electrons?

To do that, you need to look at the of iodine, which looks like this

##"I: " 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^5 52^2 4d^10 5p^5##

You know that the are defined as being the electrons located on the highest energy level of that atom, which is given by the principal quantum number, ##n##.

Notice that, in iodine's case, the highest energy level is ##n=5##. You have two subshells occupied with electrons on this energy level, ##5s^2## and ##5p^5##.

This means that iodine has a total of

##underbrace(2e^(-))_(color(blue)("from 5s subshell")) + overbrace(5e^(-))^(color(red)("from 5p subshell")) = "7 valence " e^(-)##

The rest of the electrons will thus be core electrons.

##n_"core" = n_"total" - n_"valence"##

##n_"core" = 53 - 7 = color(green)("46 core "e^(-))##

Therefore, a neutral iodine atom has ##46## core electrons and ##7## .