Bohr Model Diagram Maker
Make Bohr model diagrams of the first 20 elements, ions and isotopes, with protons and neutrons counted in the nucleus and electrons on 2, 8, 8 shells, plus Bohr-Rutherford diagrams. Written for school science.
Bohr model examples
Four Bohr models: a labeled magnesium atom, a simple carbon atom, H, Li and Na compared, and a blank worksheet with empty shells. Each is a real render of the prompt shown; click one to load that prompt and edit it.
Sodium's Bohr model, and how to draw one for any element
The labeled diagram here is a sodium-23 atom. Every element from hydrogen to calcium is drawn in the same four steps; only the numbers change.
- 1
Count the nucleus
Atomic number 11 gives 11 protons; mass number 23 − 11 gives 12 neutrons.
- 2
Two electrons on the first shell
A neutral atom has one electron per proton, 11 here, and the innermost shell takes 2, its limit.
- 3
Eight on the second
The next 8 go evenly around the second circle, which is then full.
- 4
The rest on the outer shell
One electron is left for shell 3: sodium's single valence electron, the one it loses to become Na⁺.
Bohr models element by element: hydrogen to calcium, ions, isotopes and spectra
What changes from one Bohr model to the next is the number of shells, how full the outer one is and what sits in the nucleus. The table further down lists every element to calcium; these are the groups that draw differently.
Bohr model of hydrogen and helium
Period 1: a single shell. Hydrogen-1: 1 proton, 0 neutrons, 1 electron — the only common atom with no neutron. Its isotopes differ only in the nucleus: deuterium has 1 neutron, tritium 2. Helium-4: 2 protons, 2 neutrons, 2 electrons, which fill the first shell; a full outer shell is why helium does not react.
Bohr models of lithium to neon
Period 2: two shells, 2 on the first and 1 to 8 on the second. Lithium-7 3 p, 4 n, 2, 1 · beryllium-9 4 p, 5 n, 2, 2 · boron-11 5 p, 6 n, 2, 3 · carbon-12 6 p, 6 n, 2, 4 · nitrogen-14 7 p, 7 n, 2, 5 · oxygen-16 8 p, 8 n, 2, 6 · fluorine-19 9 p, 10 n, 2, 7 · neon-20 10 p, 10 n, 2, 8. Many courses place the first four outer electrons singly, top, right, bottom, left, before pairing any, so carbon shows four lone electrons, the same pattern as its Lewis dot symbol.
Bohr models of sodium to argon
Period 3: three shells, 2 and 8 on the inner two and 1 to 8 on the third. Sodium-23 11 p, 12 n, 2, 8, 1 · magnesium-24 12 p, 12 n, 2, 8, 2 · aluminum-27 13 p, 14 n, 2, 8, 3 · silicon-28 14 p, 14 n, 2, 8, 4 · phosphorus-31 15 p, 16 n, 2, 8, 5 · sulfur-32 16 p, 16 n, 2, 8, 6 · chlorine-35 17 p, 18 n, 2, 8, 7 · argon-40 18 p, 22 n, 2, 8, 8. Check argon: its common isotope is argon-40, so it has 22 neutrons, four more than its protons.
Bohr model of potassium and calcium
Four shells. Potassium-39: 19 p, 20 n, 2, 8, 8, 1. Calcium-40: 20 p, 20 n, 2, 8, 8, 2. The fourth shell starts while the third holds only 8, because the 4s orbital is lower in energy than 3d; the third shell fills up toward 18 only from scandium on, which is 2, 8, 9, 2. Draw K and Ca with 8 on the third ring, not 9 or 10.
Bohr model of an ion
Same nucleus, different electron count. Na⁺: 11 p, 12 n, 10 electrons, 2, 8 — the outer shell is gone. Cl⁻: 17 p, 18 n, 18 electrons, 2, 8, 8. Mg²⁺ is 2, 8; O²⁻ (8 p, 8 n) and F⁻ (9 p, 10 n) are 2, 8 as well, the arrangement of neon; Ca²⁺ is 2, 8, 8. Put the ion in square brackets with the charge at the upper right. To show ionic bonding, draw Na and Cl side by side with an arrow moving sodium's outer electron onto chlorine.
Bohr–Rutherford diagram
A Bohr model that writes the nucleus out: 11 p⁺ and 12 n⁰ inside a circle for sodium, the electrons as dots on the rings around it, often with the symbol and the mass number beside it. It is the format to use for isotopes, which share an electron arrangement and differ only in the nucleus: carbon-12 has 6 neutrons and carbon-14 has 8, both drawn 2, 4; chlorine-35 has 18 neutrons and chlorine-37 has 20, both 2, 8, 7.
Hydrogen energy levels and emission lines
The diagram Bohr built his model for. The levels have energy −13.6 eV / n²: −13.6 eV at n = 1, −3.40 at n = 2, −1.51 at n = 3, −0.85 at n = 4, closer together as n grows. An electron falling to n = 2 gives the visible Balmer lines: 656 nm red from n = 3, 486 nm blue-green from n = 4, 434 nm and 410 nm violet from n = 5 and 6. Falls to n = 1 give the ultraviolet Lyman series, falls to n = 3 the infrared Paschen series. Draw it as rings with arrows between them, or as an energy ladder.
Bohr model electron arrangements of the first 20 elements
Protons, neutrons in the most common isotope, and electrons per shell for hydrogen to calcium — the numbers a Bohr model diagram of each element is checked against.
| Element | Protons | Neutrons | Electrons per shell |
|---|---|---|---|
| Hydrogen (H-1) | 1 | 0 | 1 |
| Helium (He-4) | 2 | 2 | 2 |
| Lithium (Li-7) | 3 | 4 | 2, 1 |
| Beryllium (Be-9) | 4 | 5 | 2, 2 |
| Boron (B-11) | 5 | 6 | 2, 3 |
| Carbon (C-12) | 6 | 6 | 2, 4 |
| Nitrogen (N-14) | 7 | 7 | 2, 5 |
| Oxygen (O-16) | 8 | 8 | 2, 6 |
| Fluorine (F-19) | 9 | 10 | 2, 7 |
| Neon (Ne-20) | 10 | 10 | 2, 8 |
| Sodium (Na-23) | 11 | 12 | 2, 8, 1 |
| Magnesium (Mg-24) | 12 | 12 | 2, 8, 2 |
| Aluminum (Al-27) | 13 | 14 | 2, 8, 3 |
| Silicon (Si-28) | 14 | 14 | 2, 8, 4 |
| Phosphorus (P-31) | 15 | 16 | 2, 8, 5 |
| Sulfur (S-32) | 16 | 16 | 2, 8, 6 |
| Chlorine (Cl-35) | 17 | 18 | 2, 8, 7 |
| Argon (Ar-40) | 18 | 22 | 2, 8, 8 |
| Potassium (K-39) | 19 | 20 | 2, 8, 8, 1 |
| Calcium (Ca-40) | 20 | 20 | 2, 8, 8, 2 |
Two conventions exist past calcium. School diagrams use 2, 8, 8 for the first 20 elements, as here; from scandium on, the third shell fills up toward its 18 — iron is 2, 8, 14, 2. Say which your course uses and the diagram follows it.
Bohr model vs quantum mechanical model: what is the difference?
The Bohr model puts each electron on a fixed circular orbit at a set distance from the nucleus; the quantum mechanical model replaces orbits with orbitals — regions where an electron is likely to be found — described by four quantum numbers. Bohr's numbered energy levels live on in the modern model as the principal quantum number n.
| Bohr model (1913) | Quantum mechanical model | |
|---|---|---|
| Where the electrons are | On fixed circular orbits | In orbitals — probability clouds with no set path |
| Energy levels | Quantized, numbered n = 1, 2, 3… | Quantized shells n, split into s, p, d and f subshells |
| Quantum numbers | One (n) | Four (n, l, mₗ, mₛ) |
| Atoms it describes exactly | Hydrogen and one-electron ions such as He⁺ | All atoms and molecules |
| What it explains | The hydrogen line spectrum | Spectra, chemical bonding, magnetism and the layout of the periodic table |
| Best used for | Counting protons, neutrons and electrons per shell; valence electrons | Electron configurations, orbital shapes, molecular orbital diagrams |
Use the Bohr model for what it gets right: electrons per shell and valence electrons. For orbital shapes, subshells or bonding, draw an electron configuration or a molecular orbital diagram instead.
What is a Bohr model diagram?
A Bohr model diagram draws an atom as a small nucleus — its protons and neutrons counted inside — with the electrons on concentric circular shells around it, filled from the innermost shell outward. The number of protons is the atomic number, protons plus neutrons is the mass number, and the electrons on the outer shell are the valence electrons that decide how the element bonds.
Key facts
- Niels Bohr proposed it in 1913 for the hydrogen atom. Electrons move only in allowed orbits of fixed energy and give out or take in light only when they jump between them — which reproduced the hydrogen line spectrum and the Rydberg constant.
- A shell holds at most 2n² electrons — 2, 8, 18, 32. That is 2 in the first shell, 8 in the second and 18 in the third.
- School diagrams fill the third shell only to 8 for the first 20 elements. After argon the next electrons go into 4s, which lies below 3d, so potassium is drawn 2, 8, 8, 1 and calcium 2, 8, 8, 2 — although the third shell could hold 18.
- Neutrons = mass number − atomic number. Sodium-23 has 11 protons and 23 − 11 = 12 neutrons; carbon-12 has 6 of each. A neutral atom has as many electrons as protons.
- It is a teaching model, not the modern picture. Fixed orbits cannot explain atoms with more than one electron; the quantum mechanical model replaced them with orbitals, and molecular orbital theory carries that on to chemical bonds.
Common questions about Bohr model diagrams
What should a labeled Bohr model diagram include?
The nucleus with its number of protons and neutrons, each electron shell drawn as a circle, the electrons as dots or crosses on the shells, and the count on each shell. Many worksheets also ask for the element symbol, atomic number and mass number. That is the default — ask for fewer labels and only those are drawn.
What is a Bohr–Rutherford diagram?
A Bohr–Rutherford diagram is a Bohr model with the nucleus written out: the number of protons (p⁺) and neutrons (n⁰) inside it, and the electrons drawn on the shells around it. The name, used in many Canadian science courses, credits Rutherford's nucleus of 1911 and Bohr's shells of 1913. Ask for one by name and the nucleus is labeled in that form.
How many electrons go in each shell of a Bohr model?
2 in the first shell, 8 in the second and, for the first 20 elements, 8 in the third before the fourth begins. The upper limit is 2n² — 2, 8, 18, 32 — but the 4s subshell fills before 3d, so potassium is 2, 8, 8, 1, not 2, 8, 9.
How do I find the number of neutrons for a Bohr model?
Subtract the atomic number from the mass number. Oxygen-16 has 8 protons and 16 − 8 = 8 neutrons; chlorine-35 has 17 protons and 18 neutrons. If no isotope is given, use the most common one — the table above lists it for the first 20 elements.
How do I draw a Bohr model of an ion?
Keep the nucleus the same and add or remove electrons on the outer shell. Na⁺ loses its single outer electron and is drawn 2, 8 with 11 protons; Cl⁻ gains one and is drawn 2, 8, 8 with 17 protons, usually in square brackets with the charge at the upper right.
What is the difference between a Bohr model and a Lewis dot diagram?
A Bohr model draws every shell and every electron; a Lewis dot diagram shows only the valence electrons, as dots around the element symbol. Sodium is 2, 8, 1 on a Bohr model and Na with a single dot as a Lewis symbol. For whole molecules, the Lewis structure generator on this site draws the bonds and lone pairs.
Why is the Bohr model wrong?
It is incomplete rather than wrong. Fixed circular orbits clash with the uncertainty principle and cannot predict the spectra of atoms with more than one electron; the quantum mechanical model replaced them with orbitals in the 1920s. It stays in textbooks because its shells and electron counts are still right and easy to draw.
Who created the Bohr model?
Niels Bohr, in 1913, building on Ernest Rutherford's nuclear atom of 1911. Bohr received the 1922 Nobel Prize in Physics for his work on the structure of atoms and the radiation they give out.
Can I make a simple Bohr model for younger students?
Yes — ask for a simple version and the diagram drops to the essentials: the nucleus with its counts and the electrons on each shell, five labels or fewer.
Keep exploring
Our other diagram tools, and the guides behind them.
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