1. Atomic weight of an element is the mass of an atom of that element in grams.   True   False   2. Atomic number of an element is the number of neutrons present in the nucleus of the atom.   True   False   3. Of a proton, neutron and an electron, the electron is the lightest.   True   False   4. Electrons revolve around the nucleus in shells or orbits.   True   False   5. Isotopes differ in the number of neutrons they have in their nucleus.   True   False   6. Electrons are present in the nucleus.   True   False   7. The atom is mainly empty.   True   False