An electron carries a charge of −1 elementary charge, a proton carries +1, and a neutron carries 0. Electrons are negative, protons are positive, and neutrons have no charge at all. The electron and proton charges are the same size with opposite signs, which is why ordinary matter usually ends up balanced and neutral.
The Exact Charge of Each Particle
- Electron: −1e, or −1.602176634×10⁻¹⁹ coulomb.1Wikipedia. 2019 revision of the SI
- Proton: +1e, or +1.602176634×10⁻¹⁹ coulomb.2Wikipedia. 2019 revision of the SI
- Neutron: 0.
Scientists call this basic amount of charge the elementary charge, written e.3Wikipedia. 2019 revision of the SI Since 2019 its value has been fixed exactly by definition, not measured, as part of the international system of units.4Wikipedia. 2019 revision of the SI That means the long string of digits has no uncertainty at all.
A coulomb is the everyday unit of charge, the kind you’d talk about when charge flows through a wire. One coulomb equals the combined charge of about 6.24 billion billion electrons.
Getting that number in the first place took a while. After J.J. Thomson discovered the electron in 1897, the next challenge was measuring its charge on its own.5APS News. August, 1913: Robert Millikan Reports His Oil Drop Results Early tries timed falling clouds of charged water droplets and gave only rough estimates.6APS News. August, 1913: Robert Millikan Reports His Oil Drop Results Robert Millikan’s oil drop experiment, reported in 1913, measured the unit of charge precisely.7APS News. August, 1913: Robert Millikan Reports His Oil Drop Results
Most chemistry and physics questions ask for charge in units of e, so the answers are −1, +1, and 0. Coulombs come in when the problem asks for a total, such as the charge of a given number of electrons. Then you multiply the count by 1.602176634×10⁻¹⁹. A frequent slip is dropping the sign: electrons are negative, so any quantity of them gives a negative total. If a problem gives a charge in coulombs and asks how many electrons it represents, divide by the basic unit of charge and ignore the sign for the count.
Why the Proton Is Positive and the Neutron Is Neutral
Protons are made of three smaller particles called quarks.8Wikipedia. Proton Two are “up” quarks with +2/3e each and one is a “down” quark with −1/3e.9Quanta Magazine. Inside the Proton, the ‘Most Complicated Thing’ Imaginable Add them up and +2/3 + 2/3 − 1/3 comes to exactly +1.10Quanta Magazine. Inside the Proton, the ‘Most Complicated Thing’ Imaginable
A neutron has one up quark and two down quarks. So +2/3 − 1/3 − 1/3 equals 0, giving no net charge. But the charged quarks inside are not spread evenly.11PubMed Central. Measurement of the neutron charge radius and the role of its constituents The neutron has a slightly negative charge on its outer region, and its charge doesn’t fully cancel point by point.12PubMed Central. Measurement of the neutron charge radius and the role of its constituents In one analysis, its very center was found to be negatively charged, which surprised many physicists.13PubMed. Charge densities of the neutron and proton
That’s the catch with the word neutral. It describes the total after every positive and negative contribution is added, not an absence of charged parts. The neutron’s interior holds both signs, and because they aren’t spread identically, the charge distribution inside can be mapped even though the total is zero.
You never see a third of a charge because quarks are never found alone. They stay bound in groups, so every free particle we observe carries a whole-number multiple of e.
The electron needs no such recipe. As far as anyone has been able to tell, it is not built from smaller pieces, so its −1 is a basic property rather than a sum. The proton’s charge is assembled from fractions yet comes out exactly the same size as the electron’s.
Are Proton and Electron Charges Exactly Equal
Measurements on an isolated object found any mismatch is smaller than 0.8×10⁻¹⁹ of the charge.14Physical Review. Search for an Electron-Proton Charge Inequality by Charge Measurements on an Isolated Macroscopic Body On the largest scale, the evenness of the leftover glow from the Big Bang limits any excess charge to under 10⁻²⁶e per proton across the universe.15Journal of Cosmology and Astroparticle Physics. Constraints on the electrical charge asymmetry of the universe
That precision matters because even a slight mismatch would leave every atom with a small leftover charge instead of being neutral. The leftover would have the same sign for every atom of a material, so it would add up across the huge number of atoms in an object.
Some physicists still hunt for hypothetical particles carrying tiny fractions of e, such as a thousandth of it, which no known particle has. None has been found so far, so the textbook charges remain the whole story.
Why Electrons Are Called Negative
Around 1750 Benjamin Franklin knew of two kinds of charge, depending on what was rubbed.16NASA. The Direction Assigned to Electric Currents He thought one meant extra “electric fluid”, which he called positive, and the other a shortage, called negative.17NASA. The Direction Assigned to Electric Currents Which was which was arbitrary.18Wikipedia. Fluid theory of electricity So when electrons were found, they landed on the negative side. His idea of positive flow is also the basis of “conventional current,” still used in circuit diagrams.19Wikipedia. Fluid theory of electricity
That history causes real confusion in circuits. Conventional current is drawn running from the positive terminal toward the negative one. In a metal wire, though, the moving particles are electrons, and they drift from negative to positive. Both descriptions give identical predictions for brightness, heating, and everything else you calculate. Students commonly trip by mixing the two directions within one problem, so it helps to pick one and say which you’re using.
Franklin got something right. His central idea, that an object becomes charged by gaining or losing something, turned out to be correct. The something is electrons, not a positive fluid, so a positively charged object is one that is short of electrons.
How These Charges Explain Static Electricity
When different materials touch, electrons can transfer from one to the other.20Encyclopedia Britannica. static electricity The material losing electrons has more protons than electrons and becomes positive.21Encyclopedia Britannica. static electricity The material gaining electrons becomes negative.22Encyclopedia Britannica. static electricity Repeated contact can build up more charge.23Encyclopedia Britannica. static electricity It is almost always electrons that move, because protons are locked in atomic nuclei.
A doorknob shock shows the whole chain. As you walk, your shoes rub the carpet and pick up extra electrons, so your body becomes negatively charged. The charge stays on you because nothing you touch lets it drain away. When your fingertip nears a metal doorknob, the electrons jump the small gap as a spark, the quick sting you feel. Dry winter air makes this worse, since moisture on surfaces normally helps charge leak away.
A rubbed balloon sticks to a wall for a related reason. It picks up extra electrons from your hair, and its charge nudges electrons in the wall away. The nearby wall surface turns slightly positive and attracts the balloon.
The same attraction between charges works inside atoms. The pull between positive nuclei and negative electrons keeps electrons bound. Electrons also push on each other, and the balance of pull and push helps set an atom’s energy levels.24The Journal of Chemical Physics. Roles of nuclear attraction and electron repulsion energies in the relative stability of atomic LS terms
Antiparticles Have the Opposite Charges
A basic symmetry of physics says antiparticles match their matter partners in mass but carry the opposite charge.25PubMed. High-precision comparison of the antiproton-to-proton charge-to-mass ratio Matter and antimatter should therefore be mirror images with opposite charges.26Physics Magazine. Antihydrogen Measurement Sharpens Antimatter Symmetry Test The positron carries +1e and the antiproton −1e. The antineutron is still neutral overall, but its quarks are anti-quarks with reversed charges. Precise comparisons of protons and antiprotons have so far matched this prediction.27PubMed. High-precision comparison of the antiproton-to-proton charge-to-mass ratio