Helium (symbol He, atomic number 2) is an inert noble gas used to cool superconducting magnets and to lift balloons. It is classified as a noble gas and sits in group 18, period 1 of the periodic table.
Overview
Helium is the chemical element with atomic number 2 and the symbol He. With a standard atomic weight of 4.0026, it is a noble gas. In the periodic table it occupies group 18 and period 1, and under standard conditions it is normally a gas. Helium is an inert noble gas used to cool superconducting magnets and to lift balloons.
Atomic structure
An atom of Helium has 2 protons in its nucleus and, when neutral, 2 electrons arranged in the configuration 1s2. Its standard atomic weight of 4.0026 reflects the natural mix of its stable isotopes.
Discovery and place in the table
Helium was discovered in 1868 by Pierre Janssen, Norman Lockyer. It follows Hydrogen (H) and precedes Lithium (Li) in order of atomic number.
| Atomic number | 2 |
|---|---|
| Symbol | He |
| Atomic mass | 4.0026 |
| Category | Noble gas |
| Group | 18 |
| Period | 1 |
| Electron configuration | 1s2 |
| Phase at STP | Gas |
| Discovered | 1868 (Pierre Janssen, Norman Lockyer) |