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Element 2 · Helium (He)

Helium Bohr model: diagram and electrons per shell

The helium Bohr model shows a helium atom (He) as a small nucleus with its electrons circling it in 1 shell: 2 in shell K. This page has a rotating 3D helium Bohr model, a flat diagram, a table of the electrons in each shell and the steps to draw it yourself.

Rotate the helium Bohr model in 3D

Drag to orbit, scroll to zoom.

This is a Bohr model of helium (He), a simplified picture of a single helium atom. Its nucleus holds 2 protons, and a neutral helium atom has 2 electrons, arranged around it in 1 shell (2 in shell K).

He K · 21s2

Helium Bohr model diagram

Bohr model diagram of helium: a nucleus of 2 protons with 2 electrons on 1 shell, 2 in shell K, each ring labelled with its shell letter.
The helium Bohr model drawn flat: each ring is a shell, labelled with its letter, and every dot is an electron (2 in shell K).

Helium electrons per shell

A neutral helium atom has 2 electrons, one for each of its 2 protons. They fill the shells from the nucleus outwards: 2 in shell K.

Electrons in each shell of the helium Bohr model
ShellShell number (n)ElectronsMost it can hold (2n²)Subshells
K1221s2

How the helium Bohr model builds up, shell by shell

Watch the helium Bohr model come together: the nucleus first, then each shell in turn, from the innermost outwards, with its electrons joining the ring. The legend names every shell and counts its electrons, so you can read off the arrangement (2 in shell K) as it forms.

Animation of the helium Bohr model being built: a nucleus of 2 protons appears first, then each shell grows in around it and takes its electrons, giving 2 electrons on 1 shell (2 in shell K).
The helium Bohr model built up in six seconds: the nucleus first, then each shell with its electrons, ending with 2 in shell K. Protons are red, neutrons yellow and electrons blue.

How to draw the helium Bohr model

  1. Find the atomic number. Helium has atomic number 2, so a neutral atom has 2 protons and 2 electrons.
  2. Draw the nucleus. Put a circle in the centre and write He in it. The 2 protons sit there with the neutrons.
  3. Draw the shells. Sketch 1 shell as rings around the nucleus. A shell holds at most 2n² electrons: 2 in the first, 8 in the second, 18 in the third and 32 in the fourth.
  4. Place the electrons. Fill from the inside out: 2 in shell K.
  5. Check the total. 2 = 2, the atomic number, so every electron is accounted for.

Atomic data for the helium Bohr model

The numbers behind the helium Bohr model, grouped by topic. Radii are in picometres (pm) and energies in kilojoules per mole (kJ/mol).

Identity

Symbol
He
Atomic number
2
Atomic mass
4.0026 u
Family
Noble Gases
Position
group 18, period 1
Block
s-block

Electron configuration

Full
1s2
Shorthand
1s2
Electrons per shell
2
Outer-shell electrons
2 in shell K

Ionisation energies

I₁
2372.3
I₂
5250.5

Energy to remove each electron in turn (kJ/mol). A sharp jump means the next electron comes from an inner shell.

Atomic radii

Calculated (pm)
31
Empirical (pm)
120
Covalent (pm)
46
Van der Waals (pm)
140

Electronegativity and electron affinity

Electron affinity (kJ/mol)
-48

Physical properties, abundance and history of helium

Bulk properties of helium, how common it is, who discovered it and some of its compounds.

Physical properties

Phase at room conditions
Gas
Appearance
Colorless gas, exhibiting a red-orange glow when placed in a high-voltage electric field
Melting point
-272.2°C (0.95 K)
Boiling point
-268.93°C (4.222 K)
Density
0.0001786 g/cm³
Thermal conductivity (W/m·K)
0.152
Specific heat (J/g·K)
5.193
Heat of vaporisation (kJ/mol)
0.08

Abundance

Earth's crust (mg/kg)
0.008
Oceans (mg/L)
0

Discovery

Discovered by
Pierre Janssen
Year
1868

Common compounds

  • Helium He
  • Helium-3 He
  • Hematoporphyrin D H2HeI2
  • Helium, mixt. with oxygen HeO2
  • Trimix HeN2O2
  • Helium, compd. with neon (1:1) HeNe
  • Helium--water (1/1) H2HeO
  • Helium-hydrogen fluoride FHHe

Compounds listed in the PubChem database.

Main isotopes of helium

Isotopes of helium share the same 2 protons but differ in neutrons. Natural isotopes come first, then the longest-lived others.

Main isotopes of helium: mass number, abundance, half-life and decay
Mass numberNatural abundanceHalf-lifeDecay
30 %stable–
4100 %stable–
6–806.92 msβ⁻, β⁻d
7–2.51 zsn
8–119.5 msβ⁻, β⁻n, β⁻t
9–2.5 zsn

α = alpha decay, β⁻ = beta-minus, β⁺ = beta-plus, EC = electron capture, SF = spontaneous fission, p / n = proton / neutron emission.

More about helium