Helium (He)
Helium was spotted in the Sun's light spectrum in 1868, decades before it was found on Earth.
Helium properties
- Atomic mass
- 4.0026 u
- Category
- Noble gas
- Group
- 18
- Period
- 1
- Block
- s-block
- Melting point
- 0.95 K (-272.2 °C)
- Boiling point
- 4.22 K (-268.9 °C)
- Density
- 0.179 g/L
- Atomic radius
- 140 pm
- Ionization energy
- 24.587 eV
- Electron affinity
- —
- Radioactive
- No, has stable isotopes
- Discovered
- 1868
Helium electron configuration
- Full electron configuration
- 1s2
- Electron shells
- 2
The electron configuration of Helium (He) is 1s2. Its 2 electrons are arranged in shells as 2.
Protons, neutrons and electrons in Helium
A neutral Helium atom has 2 protons and 2 electrons. Most Helium atoms have about 2 neutrons: the atomic mass rounded to 4, minus the atomic number 2.
Neutrons are approximate: atoms of the same element can have different numbers of neutrons (isotopes). Atomic number and mass
How many valence electrons does Helium have?
2
Helium has 2 valence electrons in its outermost shell, shell 1. These are the electrons involved in chemical bonding.
Helium orbital diagram
Each box is an orbital that holds up to two electrons with opposite spins (↑↓). The inner shells are the same as the noble gas in brackets. How to write electron configurations
Molar mass of Helium
4.0026 g/mol
One mole of Helium atoms (6.022 × 10²³ atoms) has a mass of 4.0026 grams. Use this value to convert between grams and moles.
Helium facts
- Helium was spotted in the Sun's light spectrum in 1868, decades before it was found on Earth.
- At normal pressure helium never freezes, even at absolute zero.
- Helium (He) has atomic number 2 and is a gas at room temperature. It was discovered in 1868.
Position in the periodic table
Helium is element 2, in period 1 and group 18 of the periodic table, in the s-block.
Uses of Helium
Helium is used as a liquid, at about −269 °C, to cool the superconducting magnets in MRI scanners. Because it is lighter than air and does not burn, it fills party balloons, weather balloons and airships. Engineers also use helium to find tiny leaks, as a shielding gas in welding and to purge rocket fuel tanks, and deep-sea divers breathe it mixed with oxygen.
Who discovered Helium?
Helium was discovered in 1868, when astronomers Pierre Janssen and Norman Lockyer observed an unexplained yellow line in the Sun's spectrum and Lockyer proposed that it came from a new element. William Ramsay first isolated helium on Earth in 1895, from a uranium mineral called cleveite.
Where does the name come from?
Helium is named after helios, the Greek word for the Sun. Astronomers first detected it in 1868 as an unexplained yellow line in sunlight, decades before anyone found the gas on Earth.
Same group
Compare Helium
FAQ
What is the electron configuration of Helium?
The electron configuration of Helium (He) is 1s2. Its 2 electrons are arranged in shells as 2.
How many protons, neutrons and electrons does Helium have?
A neutral Helium atom has 2 protons and 2 electrons. Most Helium atoms have about 2 neutrons: the atomic mass rounded to 4, minus the atomic number 2.
How many valence electrons does Helium have?
Helium has 2 valence electrons in its outermost shell, shell 1. These are the electrons involved in chemical bonding.
What is the molar mass of Helium?
The molar mass of Helium is 4.003 g/mol. This is the same number as its atomic mass, 4.003 u.
Is Helium a metal?
No. Helium is a noble gas, so it is a nonmetal.
Is Helium radioactive?
Ordinary Helium is not radioactive: it has at least one stable isotope. Like every element, it also has radioactive isotopes, most of them made in laboratories.
Where is Helium on the periodic table?
Helium is element 2, in period 1 and group 18 of the periodic table, in the s-block.