1). OF COURSE the atom's mass is more than the mass of its protons
and electrons. They left out the neutrons ! A neutron has roughly the
same mass as a proton has, and there's a neutron for every proton in
the Carbon nucleus. So if you ignore the neutrons, you miss almost
half of the mass of the whole atom.
2). OK, here's a riddle: What do you call a substance that's shiny and
a good conductor of electricity ?
Here are some examples: Gold, silver, copper, iron, aluminum, mercury.
How about "metals" ?
