Question

Given following electron configurations,

1s22s22p63s23p64s23d104p65s24d9 and 1s22s22p63s23p64s23d104p65s14d10.

Part 1: Name the element.

Part 2: Both electron configurations are correct, and the second one is what is found most often in nature. Suggest a reason for why this element most often exists as an exception to the normal electron configuration rules.

Answer 1

Both the configurations represent the same element since they both have the same number of electrons (notice how the second configuration simply has one of the outer electrons in the 4d block instead of the 5s block.

To find the element simply add up the total # of electrons. Since this is a neutral atom, # of electrons = # of protons = # atomic number, so you can simply look for the appropriate atomic number on the periodic table.

Here’s one if you need it: ptable.com

Answer 2

For part 2, notice how the second configuration has its outermost shell filled (d shells carry a max of 10 electrons) which is much more energetically stable than the partially filled shell in the first configuration.