No, it is not true that a chlorine atom has one more electron than a chloride ion. In fact, a chloride ion has one more electron than a chlorine atom.

A chlorine atom has 17 protons and 17 electrons, giving it a neutral charge. A chloride ion has 17 protons and 18 electrons, giving it a negative charge. The extra electron in the chloride ion is what gives it its negative charge.