Helium atom

Helium atom
	Helium-4
Names
	Systematic IUPAC name Helium
Identifiers
CAS Number	7440-59-7 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:33681 ;
ChemSpider	22423 ;
EC Number	231-168-5;
Gmelin Reference	16294
KEGG	D04420 ;
MeSH	Helium
PubChem CID	23987;
RTECS number	MH6520000;
UNII	206GF3GB41 ;
UN number	1046
	InChI InChI=1S/He Key: SWQJXJOGLNCZEY-UHFFFAOYSA-N ;
	SMILES [He];
Properties
Chemical formula	He
Molar mass	4.002602 g·mol−1
Appearance	Colourless gas
Boiling point	−269 °C (−452.20 °F; 4.15 K)
Thermochemistry
Std molar; entropy (S⦵298)	126.151-126.155 J K−1 mol−1
Pharmacology
ATC code	V03AN03 (WHO)
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

A helium atom is an atom of the chemical element helium. Helium is composed of two electrons bound by the electromagnetic force to a nucleus containing two protons along with two neutrons, depending on the isotope, held together by the strong force. Unlike for hydrogen, a closed-form solution to the Schrödinger equation for the helium atom has not been found. However, various approximations, such as the Hartree–Fock method, can be used to estimate the ground state energy and wavefunction of the atom.

Historically, the first attempt to obtain the helium spectrum from quantum mechanics was done by Albrecht Unsöld in 1927. Egil Hylleraas obtained an accurate approximation in 1929. Its success was considered to be one of the earliest signs of validity of Schrödinger's wave mechanics.