Because going down a column you are jumping up to the next higher main energy level (n) and each energy level is further out from the nucleus
Using the relative atomic weights of both copper and sulfur ie copper = 63.55 and sulfur is 32.06 so 63.55+32.06=95.56 total mass and so of this, copper = 63.55/95.56=66.4%. So to get 10 grams of copper, use the formula 10g=66.4%xCuS so CuS=10/0.664=15.06 grams of CuS.
Explanation:
sodium atom is neutral while sodium ion is a charged specie with a charge of +1
