After finishing a lab, you have some chemicals left over. You do not want to waste them, so you carefully pour them back into the container you got them from.

Instead, pour a small amount into a beaker or clean weigh dish. Once you have added a chemical to a container, label it promptly. When you are finished with the experiment, dispose of the excess chemical as chemical waste. Do not simply pour the excess chemical down the sink.

atomic mass = 39

number of neutrons = 20

number of protons= 19

electronic configuration = 1s2 2s2 2p6 3s2 3p6 4s1

the number of electron in first shell = 2

number of electrons in n=3 shell = 8