Calcium chloride contains calcium and chloride ions. write the ground-state electron configuration for the chlorine ion.

The electron configuration of an atom of Chlorine Cl (neutral Chlorine) is:

1s2 2s2 2p6 3s2 3p5

Now if the Chlorine becomes an ion, it becomes Cl-. So we can see that 1 electron is added therefore the new electron configuration is:

1s2 2s2 2p6 3s2 3p6

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.