3D model of a carbon atom showing the nucleus and electron shells

Periodic table

Click an element to build its atom. Arrow keys move around the table, Enter picks, Esc closes.

ProtonNeutronElectronValence shell
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This atom 3D model shows any of the 118 elements two ways: as a Bohr model, with electrons circling the nucleus in shells, and as a quantum model, with electrons spread through s, p, d and f orbitals. Pick an element, add or remove protons, neutrons and electrons, and the model rebuilds itself and names the isotope or ion you made.

What the atom 3D model shows

The model opens on carbon-12: 6 protons and 6 neutrons packed into the nucleus and 6 electrons around it, 2 in the first shell and 4 in the second. Drag to rotate it, scroll to zoom and click any particle to see what it is. The Element tab holds a full periodic table, so you can jump to oxygen, iron or uranium-238 in one click.

Electron numbers come from the measured ground-state configurations published by NIST, including the elements that break the usual filling order, such as chromium and copper. Isotope masses, natural abundances and half-lives come from the IAEA nuclear data tables.

Parts of an atom, labeled

Every atom is built from three particles:

ParticleChargeMass (kg)Mass (u)Where it is
Proton+11.673 × 10-271.007Nucleus
Neutron01.675 × 10-271.009Nucleus
Electron-19.109 × 10-310.000549Shells or orbitals around the nucleus

A proton is 1,836 times heavier than an electron, so more than 99.9% of an atom’s mass sits in the nucleus. Protons plus neutrons give the mass number: carbon-12 has 6 + 6 = 12. Turn on Labels in the View tab to tag each part on the model.

Bohr model vs quantum model

The Bohr model, proposed by Niels Bohr in 1913, puts electrons on fixed circular paths at set distances from the nucleus. Each path is a shell, or energy level. The model correctly predicts how many electrons fit in each shell and explains why hydrogen gives off light only at certain colors. It is the model most school textbooks draw, and it is the default view here.

The quantum model, built on Erwin Schrödinger’s 1926 wave equation, replaces paths with orbitals. An orbital is a region where an electron is likely to be found. An electron has no exact position until it is measured, so the model shows a cloud of probability instead of a dot on a track. Switch to Orbital view and each electron spreads into its cloud.

The two models agree on the shells. The Bohr model is easier for counting electrons. The quantum model shows the true shape of an atom, which is why chemists use it to explain bonding.

Electron shells and configuration

Shell n can hold up to 2n2 electrons: 2 in the first shell (K), 8 in the second (L), 18 in the third (M) and 32 in the fourth (N). For the first 20 elements the shells fill in a simple 2, 8, 8 pattern. Click any symbol to load that atom.

ElementElectrons per shellElementElectrons per shell
Hydrogen (H)1Sodium (Na)2, 8, 1
Helium (He)2Magnesium (Mg)2, 8, 2
Lithium (Li)2, 1Aluminum (Al)2, 8, 3
Beryllium (Be)2, 2Silicon (Si)2, 8, 4
Boron (B)2, 3Phosphorus (P)2, 8, 5
Carbon (C)2, 4Sulfur (S)2, 8, 6
Nitrogen (N)2, 5Chlorine (Cl)2, 8, 7
Oxygen (O)2, 6Argon (Ar)2, 8, 8
Fluorine (F)2, 7Potassium (K)2, 8, 8, 1
Neon (Ne)2, 8Calcium (Ca)2, 8, 8, 2

Potassium starts a fourth shell while the third holds only 8, because the 4s orbital has lower energy than the 3d orbitals. From scandium onward the 3d orbitals fill and the third shell grows toward 18. Iron, for example, is 2, 8, 14, 2.

The electrons in the outermost shell are the valence electrons. They decide how an atom bonds. Elements in the same group of the periodic table have the same number of valence electrons, which is why sodium and potassium react in the same way. The model highlights the valence shell in teal.

Orbitals: s, p, d and f shapes

Each shell splits into subshells, and each subshell into orbitals. Every orbital holds at most 2 electrons.

SubshellOrbitalsElectronsShape
s12Sphere
p36Two lobes, like a dumbbell, along the x, y or z axis
d510Four-leaf clover, plus one dumbbell with a ring
f714More complex, most with six or eight lobes

Carbon’s configuration, 1s2 2s2 2p2, reads as 2 electrons in the 1s orbital, 2 in 2s and 2 in the 2p subshell. The 2 p electrons sit in separate p orbitals before they pair up, a pattern called Hund’s rule, and the model draws them that way. Use Colour by phase to see the two lobes of each p orbital in different colors. The colors mark the sign of the electron’s wave, which matters when orbitals of two atoms overlap to form a bond.

The orbital shapes come from the hydrogen atom’s wave equation, with the lobes drawn a little tighter so they stand out. For atoms with more electrons the model uses the same shapes and sizes them with Slater’s rules, the standard textbook method for estimating how strongly each electron feels the nucleus.

Isotopes and ions

An isotope is a version of an element with a different number of neutrons. Carbon-12 has 6 neutrons and makes up 98.93% of natural carbon. Carbon-13 has 7. Carbon-14 has 8 and is radioactive, with a half-life of about 5,700 years, which is what makes radiocarbon dating work. Hydrogen’s isotopes have their own names: protium (no neutrons), deuterium (1) and tritium (2).

An ion is an atom that has gained or lost electrons, so it carries a charge. Sodium loses its single outer electron to become Na+ with shells 2, 8. Chlorine gains one to become the chloride ion, Cl-, with shells 2, 8, 8. Both end up with a full outer shell, and together they make table salt. The Isotope & ion tab lists every isotope of the element you pick and lets you add or remove charge.

Changing the number of protons changes the element. Changing the neutrons makes a different isotope. Changing the electrons makes an ion. The Build tab lets you test all three.

How big is an atom?

A hydrogen atom is about 0.1 nanometers across. Its nucleus, a single proton, is about 63,000 times smaller. If the atom were the size of a 100-meter football field, the nucleus would be a dot 1.6 millimeters wide on the center spot. Almost all of an atom is empty space.

A model drawn to that scale would show nothing but a ring with an invisible center, so this model, like every textbook diagram, draws the nucleus far larger than it is. The distances between shells are not to scale either. The orbital view keeps the relative sizes of the orbitals of one atom correct.

How to make a 3D atom model for school

A model for a science project needs the right number of each particle. Get the numbers from the element’s atomic number and mass number:

For carbon-12 that is 6 protons, 6 neutrons and 6 electrons, with 2 electrons on the inner ring and 4 on the outer ring.

  1. Use foam or clay balls in two colors for protons and neutrons, about 2 to 3 cm across. Glue them into a tight ball for the nucleus.
  2. Bend wire, pipe cleaners or embroidery hoops into one ring per shell.
  3. Thread or glue smaller beads onto the rings for electrons, spaced evenly.
  4. Hang the rings around the nucleus with fishing line or push them into a foam base with wooden skewers.
  5. Add a key card that names each color and lists the element, atomic number and mass number.

Use the same colors as the model here (red protons, grey neutrons, blue electrons) and check your count in the Build tab before you glue anything.

Frequently asked questions

What are the 3 main parts of an atom?

Protons and neutrons in the nucleus, and electrons around it. Protons are positive, electrons are negative and neutrons have no charge.

What is the difference between the Bohr model and the quantum model?

The Bohr model puts electrons on fixed circular orbits called shells. The quantum model describes electrons as clouds of probability called orbitals. Both give the same number of electrons per shell.

How many electrons can each shell hold?

Up to 2n2: 2 in the first shell, 8 in the second, 18 in the third and 32 in the fourth.

What is a valence electron?

An electron in the outermost shell of an atom. Valence electrons take part in chemical bonds, and their number sets an element’s chemical behavior.

What is the difference between an isotope and an ion?

An isotope has a different number of neutrons than another atom of the same element. An ion has a different number of electrons than protons, so it carries an electric charge.

Is the nucleus in an atom model drawn to scale?

No. The nucleus is tens of thousands of times smaller than the atom. Drawn to scale, it would be too small to see, so models enlarge it.

What does an atom really look like?

An atom has no sharp edge. It is a tiny, dense nucleus inside a fuzzy cloud of electrons, which is what the orbital view shows. Microscopes such as the scanning tunneling microscope image atoms as soft bumps.

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