If an atom has a charge of -2 and an atomic number of 7, how many electrons does it have?

1 Answer
Oct 12, 2016

The atom has 9 electrons.


The atomic number for an element is the number of protons in the nuclei of their atoms. In a neutral atom, there are equal numbers of protons and electrons. Since the atom has gained a charge of #"2-"#, it now has two more electrons than protons. So the number of electrons is now #9#.

#"9e"^(-) + 7p^(+) = 2e^-"#