What gives an elemental atom its weight?

1 Answer
Oct 6, 2016

The weight derives from the massive particles in the element's nucleus.


In an isolated atom, or indeed in a collection of atoms, most of the mass is concentrated in the nucleus, which is itself composed of massive fundamental particles: #"protons"#, massive particles that are positively charged; and #"neutrons"#, massive particles that are neutrally charged. The mass of protons and neutrons are roughly equivalent, and their short range interaction overcomes electrostatic repulsion, and binds the nucleus together.

The number of protons determines the identity of the nucleus. The number of neutrons (which may vary from atom to atom) determines the isotopic mass. See here for more definitions.