Helium (He)
Helium is element 2, a noble gas in group 18, period 1. A neutral atom has 2 protons, 2 neutrons and 2 electrons, 2 of them valence electrons.
Noble gas- Atomic number
- 2
- Atomic mass
- 4.003 u
- Valence electrons
- 2
- Protons · neutrons
- 2 · 2
- Electrons per shell
- 2
- At room temperature
- gas
Bohr model of helium
The Bohr model draws helium as a nucleus of 2 protons and 2 neutrons, with its 2 electrons on 1 circular shell: 2 in shell 1. Press Build the atom to watch the shells fill from the inside out. The outer ring is dashed: the electrons there are the ones that take part in chemistry.
Real electrons don't travel in neat circles. They live in fuzzy orbitals, shown below, but the Bohr picture is the quickest way to count shells and valence electrons.
Electron configuration of helium
1s²
How many valence electrons does helium have?
Helium has 2 valence electrons.
Helium is in group 18 but has only two electrons, which fill its first and only shell. That full shell is why helium is so unreactive.
Protons, neutrons and electrons
| Protons | 2 | equal to the atomic number |
|---|---|---|
| Electrons | 2 | equal to the protons in a neutral atom |
| Neutrons | 2 | mass number 4 − 2 protons |
Atoms of the same element can have different numbers of neutrons (isotopes). The count above uses the rounded atomic mass, the way it's taught in class.
Helium properties
| Symbol | He |
|---|---|
| Category | Noble gas |
| Group · period · block | 18 · 1 · s |
| Atomic mass | 4.003 u |
| State at 25 °C | gas |
| Melting point | 0.95 K (-272 °C, -458 °F) |
| Boiling point | 4.22 K (-269 °C, -452 °F) |
| Density | 1.79e-4 g/cm³ |
| Electronegativity (Pauling) | — |
| Atomic radius | 140 pm |
| First ionization energy | 24.587 eV |
| Electron affinity | — |
| Oxidation states | 0 |
| Common ion charge | 0 |
| Discovered | 1868 by Pierre Janssen |
Where helium sits on the periodic table
Group 18: Neon, Argon, Krypton, Xenon, Radon, Oganesson.
Questions about helium
How many valence electrons does helium have?
Helium has 2 valence electrons.
How many protons, neutrons and electrons does helium have?
A neutral helium atom has 2 protons and 2 electrons. Its most common form has about 2 neutrons (mass number 4 − 2 protons).
What is the electron configuration of helium?
1s², written in short form as 1s².
What does the Bohr model of helium look like?
A nucleus of 2 protons and 2 neutrons, circled by 1 electron shell holding 2 electrons.
What is the atomic number of helium?
2. The atomic number is the number of protons in the nucleus, and it is what makes an atom helium.