Switch on a lamp, and something starts to move inside the wires. It is far too small to see, and it moves without a sound. It is a huge crowd of tiny particles called electrons.

Where do electrons live?

Everything around you is made of atoms. Every atom has a heavy middle, called the nucleus. Around the nucleus, electrons move in a fuzzy cloud.

The nucleus holds particles called protons. Protons carry a plus electric charge, and electrons carry a minus charge. Plus and minus pull on each other. That pull keeps the electrons close to their atom.

Different atoms have different numbers of electrons. A hydrogen atom has only one. A copper atom has 29, and a gold atom has 79.

How small is an electron?

Electrons are even smaller than atoms — much, much smaller. No experiment has ever found any size for an electron at all. As far as scientists can tell, it behaves like a tiny point.

Electrons are also very light. A proton weighs almost 2,000 times as much as an electron. So nearly all of an atom’s weight sits in its nucleus, not in its electrons.

One proton balances almost 2,000 electrons A balance scale stays level. On the left pan lies one proton. On the right pan lies a heap of electrons, labelled almost 2,000 electrons. 1 proton almost 2,000 electrons
One proton weighs as much as almost 2,000 electrons.

Why do metals carry electricity?

In most materials, each electron stays with its own atom. But metals are special. In a metal, some electrons are not held by any one atom.

These electrons can wander freely between the atoms, so we call them free electrons. On their own, they zoom about in all directions, like bees around a hive. All together, they go nowhere.

Now make the wire part of a loop with a battery and a lamp. The battery pushes on the free electrons, and they all start to drift the same way along the wire. This flow of electrons is called electric current. The push from the battery is called voltage.

Free electrons in a metal wire Two views of a piece of metal wire, full of atoms with free electrons between them. Top: with no push, the free electrons move in all directions. Bottom: with a push from a battery, they all drift the same way along the wire, which is an electric current. no push: electrons wander with a push: electric current metal atom free electron
Without a push, free electrons wander in all directions. With a push from a battery, they all drift the same way: that is an electric current.

That is why wires are made of metal, usually copper. Materials like copper, which let electrons flow easily, are called conductors. Materials like plastic hold on to their electrons tightly. They are called insulators.

What else do electrons do?

Carrying electric current is not their only job. Electrons are busy almost everywhere:

  • Static electricity. Rub a balloon on your hair, and some electrons jump from your hair onto the balloon. Then the balloon and your hair pull on each other.
  • Holding atoms together. Atoms join into bigger groups by sharing or swapping their outer electrons.
  • Making light. In an LED lamp, electrons give away some of their energy as light. In glowing signs, speeding electrons crash into atoms and make them shine.
Go deeper: The electron in numbers for grown-ups and the extra curious
  • Mass: about 9.11×10−319.11 \times 10^{-31} kg. That is about 1/1836 of the mass of a proton.
  • Charge: −1.602×10−19-1.602 \times 10^{-19} coulombs. A proton carries exactly the same amount of charge, but plus. No free particle has ever been found with a smaller charge.
  • Size: none that anyone has measured. The electron is an elementary particle: as far as we know, it has no smaller parts.
  • Discovery: J. J. Thomson discovered the electron in 1897. He was studying cathode rays: mysterious rays inside glass tubes with nearly all the air pumped out, which made the glass glow where they hit. He showed that the rays were made of particles far lighter than the lightest atom. The name “electron” had been suggested a few years earlier by George Johnstone Stoney, for the smallest bit of electric charge. You can meet more explorers in the history of electricity.
Go deeper: What free electrons really do for grown-ups and the extra curious

Free electrons in copper are anything but slow: they zip about at around 1,500 kilometres per second. But they keep bumping into the vibrating atoms and changing direction, so on average they get nowhere. A battery adds a slow drift in one direction on top of this — often less than a millimetre per second. In copper, each atom lends about one electron to the crowd of free electrons.

In a metal wire, the current is carried by electrons. In salty water, in the human body and in the liquid or paste inside batteries, current is carried by ions instead: atoms that have gained or lost electrons.

Check yourself

Why can electricity flow through a copper wire?

Show the answer

Some of the electrons in copper are free to move — In metals like copper, some electrons do not belong to any one atom. A push from a battery makes them drift along the wire.