The relative charge of a nucleus is the same as its proton (atomic ... charged ion if the atom gains one or more electrons, it becomes a negatively-charged ion A helium atom has two electrons ...

Precision spectroscopy of helium and ... at which an atom's dynamic polarizability becomes zero, meaning the atom does not interact with external laser light. Hyperfine Structure: The small ...

For example, a helium atom has an atomic mass of 4, but an atomic number (or positive charge) of 2. Since electrons have almost no mass, it seemed that something besides the protons in the nucleus ...