Different between chlorine and chloride

Chlorine: The greenish-yellow, highly reactive and diatomic gas that is almost never found free in nature by itself. Most Chlorine is commercially produced and is most widely known for being used within compounds to purify water and create cleaning products.

Chloride: The negatively charged ionic form of Chlorine. Since Chlorine is found deep within the Earth's crust, and is extremely reactive, the only way it can be found in nature is when it reacts with other chemicals and creates compounds. Chloride is what is created when Chlorine gains an electron and combines with other elements. Chloride is found abundantly in nature and is most commonly known for forming neutral salts such as sodium chloride (table salt), potassium chloride, and calcium chloride.

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.