Well, what's the #"atomic number"# for #"potassium"#?
Explanation:
For #K#, #Z=19#.
If #Z=19#, there must be 19 protons in the potassium nucleus, 19 fundamental, massive, positive charges. If there are 19 positive charges in the atom, how many negative charges must there be to give a net positive charge? I make it 18? Do you agree? What do we normally call these negative charges.