Electrons: Tiny Leptons Held by Electric Attraction

0:00What keeps the electrons in an atom from flying away?

0:06This is a helium atom. At its centre is the nucleus, made of two protons and two neutrons.

0:14Each proton has an electric charge of plus one and neutrons have no charge, so the nucleus is positive.

0:23Much smaller particles called electrons move around the nucleus.

0:28An electron belongs to a family of particles called leptons.

0:33Leptons are fundamental particles, which means they have no known smaller parts.

0:39An electron has an electric charge of minus one, equal and opposite to a proton's plus one.

0:47An electron's mass is tiny: about 1,836 electrons have the same mass as one proton.

0:56Neutrinos are leptons too, with no charge and almost no mass.

1:02Opposite charges attract, so the negative electrons are pulled toward the positive nucleus.

1:09This electric attraction, part of the electromagnetic force, is what holds the electrons in the atom.

1:16Gravity holds planets around the Sun, but it does not hold electrons in an atom.

1:22Between such tiny particles, gravity is far too weak to matter.

1:27This drawing is not to scale: the real nucleus is tens of thousands of times smaller across than the atom.

1:35So an atom is mostly empty space.

1:39Electrons are tiny leptons, held in the atom by electric attraction to the positive nucleus.