Nodyn:Infobox helium

hydrogen ← heliwm → lithiwm - ↑ He ↓ Ne 2He Y Tabl Cyfnodol
Ymddangosiad
Nwy diliw, er bod iddo wawr orengoch pan rhoddir ef mewn maes trydan foltedd uchel. Llinellau sbectral heliwm
Nodweddion cyffredinol
Enw, symbol, rhif	heliwm, He, 2
Teulu'r elfennau	nwy nobl
Grŵp, cyfnod, bloc	18, 1, s
Rhif atomig	4.002602(2)
Patrwm yr Electronnau	1s2
Electronnau / cragen	2 (Image)
Nodweddion ffisegol
Stâd	nwy
Dwysedd	(0 °C, 101.325 kPa) 0.1786 g/L
Dwysedd hylif / Ymdoddbwynt	0.145 g·cm−3
Ymdoddbwynt	(at 2.5 MPa) 0.95 K, −272.20 °C, −457.96 °F
Berwbwynt	4.22 K, −268.93 °C, −452.07 °F
Pwynt critigol	5.19 K, 0.227 MPa
Enthalpi ymdoddiad Gwres o ymdoddi	{{{heat fusion 2}}} kJ·mol−1
Enthalpi anweddiad	Cynhwysedd gwres	5R/2 = 20.786 J·mol−1·K−1
Vapor pressure (defined by ITS-90)
P (Pa) 1 10 100 1 k 10 k 100 k at T (K)     1.23 1.67 2.48 4.21
Nodweddion Atomig
Electronegativity	dim data (Graddfa Pauling)
egni ïoneiddiadau	1af: 2372.3 kJ·mol−1
	2: 5250.5 kJ·mol−1
Radiws cofalent	28 pm
Radiws Van der Waals	140 pm
Amrywiol
Strwythyr y crisal	hexagonal close-packed
Magnetic ordering	diamagnetic[1]
Dargludiad Thermal	0.1513 W·m−1·K−1
Cyflymder sain	972 m·s−1
CAS registry number	7440-59-7
Most stable isotopes
Main article: Isotopes of heliwm
iso NA half-life DM DE (MeV) DP 3He 0.000137%* 3He is stable with 1 neutrons 4He 99.999863%* 4He is stable with 2 neutrons *Atmospheric value, abundance may differ elsewhere.
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References

These references will appear in the article, but this list appears only on this page.

1. Magnetic susceptibility of the elements and inorganic compounds, in Handbook of Chemistry and Physics 81st edition, CRC press.