Helium Atomic Mass

  1. Atomic Number Of Helium
  2. Helium Atomic Mass Amu
IsotopeAtomic mass (Da)Isotopic abundance (amount fraction)
3He3.016 029 322(2)0.000 002(2)
4He4.002 603 2545(4)0.999 998(2)

Atomic Mass of Helium Atomic mass of Helium is 4.0026 u. Note that, each element may contain more isotopes, therefore this resulting atomic mass is calculated from naturally-occuring isotopes and their abundance. The unit of measure for mass is the atomic mass unit (amu). Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have? Of Protons + No. Of Neutrons = (No. Of electrons) = Mass number. It's average atomic mass 35.5 amu. Write the difference of neutrons between 'A' and 'B'.

In contrast to the other noble gases, which are separated for commercial use almost entirely fromair, a large amount of commercial He is derived from natural gas deposits containing relatively high concentrationsof radiogenic 4He. In its 1961 report, the Commission recommended Ar(He) = 4.0026 based onthe atomic mass of 4He to four decimal places. The abundance of 3He in airof 0.000 137 % as determined by Nier had a negligible effect on the atomic weight of helium. This isotopeis present in natural sources of helium with a smaller abundance than that of any other stable isotope relativeto its elemental composition. In 1969 the Commission recommended Ar(He) = 4.002 60(1), which was identical to the atomic mass of 4He to six significant figures.A subsequent determination of the isotopic composition of atmospheric helium have confirmed this value which has been last revised in 1983.

The indicated interval for the standard atomic weight of He has a lower limit of 4.002 600, correspondingto an abundance of x(3He) = 3.3×10-6. This interval includes some natural 3He-enrichedsources, but it does not include all helium from volcanic rocks or associated geothermal springs and gases,some of which have 3He abundances more than ten times that of atmospheric helium, hence the annotation'g'. Those types of 3He-enriched sources are considered to represent emissions of primordial heliumfrom incompletely degassed regions deep within the earth.

Helium, a noble gas, is chemically the most unreactive element with the lowest boiling point (4.2 K). Apart from its presence in gaseous or fluid inclusions and interstitial positions in crystals, andin voids in clathrate compounds, He occurs naturally only as a monoatomic gas. Helium is too light tobe held in the atmosphere by Earth's gravitation over periods comparable with the age of the earth; thus,4He in the atmosphere has been derived almost entirely from degassing of the solid earth, where it isproduced by alpha decay of heavy radioisotopes. The minor isotope 3He is believed to be largely primordial,with minor amounts derived from beta decay of 3H, which is produced by the reaction 6Li(n,α)3H in the earth, by cosmic-ray reactions in the atmosphere, or by nuclear explosions and industry.Accumulations of 3He produced by radioactive decay of anthropogenic 3H provide a useful tool for determiningages of groundwaters and surface waters, including the ocean. The physical properties of 3Hein gas, liquid, and solid phases and of 3He and 4He mixtures have been the subjects of many experimentalstudies that have contributed decisively to our understanding of quantum physics and chemistry

SOURCEAtomic weights of the elements: Review 2000 by John R de Laeter et al. Pure Appl. Chem. 2003 (75) 683-800
© IUPAC 2003

Atomic Number Of Helium


Ar(He) = 4.002 602(2) since 1983
The name derives from the Greek helios for 'sun'. The element was discovered by spectroscopy duringa solar eclipse in the sun's chromosphere by the French astronomer Pierre-Jules-Cesar Janssen in1868. It was independently discovered and named helium by the English astronomer Joseph NormanLockyer.
Helium was thought to be only a solar constituent until it was later found to be identical to the heliumin the uranium ore cleveite by the Scottish chemist William Ramsay in 1895. The Swedish chemists Per Theodore Cleve andNils Abraham Langet independently found helium in cleveite at about the same time.

From being the second lightest element to being the second in line in terms of abundance in Universe, Helium is an interesting element in the Period Table. Named after a Greek god, the element has some unique properties. In this article on interesting Helium facts, we are going to learn 30 facts, some of which may have already been known to you. Still, consider this as a refresher course. In case you need the information for your school project, feel free to use it.

But, before we start…

Element NameHelium
Element SymbolHe
Group18 of Periodic Table
BlockS of PT
Element FamilyNoble Gas
Element State at Room TemperatureGas
Atomic Number2
Atomic Mass4.002602 amu (atomic mass unit)
Crystal structureHexagonal
Number of electrons2
Number of protons2
Number of neutrons2
Density0.000164 g/cm3
Melting Point0.95K or -457.96 ºF or -272.20 ºC
Boiling Point4.222 K or -452.070 ºF or -2683928 ºC
Atomic Radius1.40 Å
Covalent Radius0.37 Å
Stable IsotopesHelium-3 (3He) and Helium-4 (4He)
3He Abundance1.34 x 10-4 % (that is, 0.00034 %)of total Helium found naturally.
4He Abundance99.999866% of Helium found naturally

1. Helium was the first element that was not discovered on Earth. It was Sun’s spectroscopy data that first revealed that existence of this element.

2. Of the total elemental mass of our known or visible universe, Helium makes up 23%. However, compared to its presence in entire universe, its abundance on Earth is very rare.

Helium Atomic Mass Amu


3. Helium is an inert gas. It is non-toxic, completely odorless, tasteless and has no color.

4. Helium belongs to the family of noble gases. There are 7 noble gases (Oganesson, Radon, Xenon, Krypton, Argon, Neon, Helium) of which, Helium has least density and it is lightest of all the noble gases.

5. When it comes to reactivity of the noble gases, neon is the least reactive while helium takes the second spot in being the least reactive noble gas.

Helium atomic mass number

6. Of all elements that exist in this universe, Helium has the lowest boiling point and lowest melting point.

7. In order to convert Helium into liquid state or solid state, one needs to apply extremely low temperatures and extremely high pressures.

8. When radioactive emissions take place through alpha-decay (α-decay), the emissions are basically Helium nuclei.

9. Helium gas when ionized, gives a glow of reddish-orange hew. It was the yellow spectral line of Helium that led to its discovery.

10. In case someone accidentally inhales Helium, the pitch of his or her voice is raised or increased.

11. At normal pressure, when the temperature is dropped to absolute zero, Helium will remain in liquid state. It is the only known element to do so.

12. Helium is the least dense and second lightest of all known elements. It is because of this, when a balloon is filled with Helium, it floats up.

13. Deep sea divers (those who dive up to 122 meters or 400 feet) use ‘Heliox’ – a breathing mixture in which, air’s nitrogen is replaced by Helium. The reason for this is that at 100 feet (that is 30 meters) or below that, nitrogen can quickly build up within the tissues of the body, causing Nitrogen narcosis or fatal decompression illness. Nitrogen narcosis is a condition which is similar to effect which occurs because of extreme and sudden drunkenness.

14. The name of Helium comes from Helios – the Greek sun god. There is a reason for this naming. This element was discovered while studying Sun’s spectroscopy data (gas absorption lines).

15. Our Sun’s 45% of the mass is composed of Helium. Actually, Hydrogen atoms in Sun fuse together to form Helium because of extreme temperatures.

16. Not just that Hydrogen is fused in Helium, even Helium atoms are fused together to form Silicon, Oxygen and Carbon – which are heavier elements compared to Helium.

17. The isotope 3He is not found on Earth. This isotope has only one neutron and two protons. This isotope is considered to be ideal for being used as fusion power generation fuel. Interestingly, large quantities of this isotope have been found on Moon. The reason why 3He is found on moon is that solar winds led to 3He rain on surface of Moon for several billion years.

18. Helium at supercool temperatures can make you go – ‘Huh?’ – it becomes superfluid and does things that no other liquid can do. When the temperature of Helium is dropped a few degrees below its boiling point (which is -452.070 ºF) (dropped below -456ºF, that is slight above Zero Kelvin), it becomes superfluid.

19. In superfluid state, Helium has zero friction and its density becomes 1/8th of that of water. It is capable of flowing through cracks which are as thin as that of the diameter of a molecule. This superfluid Helium can also climb the walls of a container and it can also stay absolutely motionless if the container in which it is kept, is spun.

20. At low temperatures, Helium can be easily converted into liquid. It is this feature that allows Helium to be used in powerful superconducting electromagnets as coolant. In Switzerland’s Geneva, Large Hadron Collider has such electromagnets and liquid Helium is used as coolant.

21. MRI scanners in hospitals have magnetic coils that are shaped like rings. These magnetic coils are cooled down to the temperature of –263ºC or –441ºF using liquid Helium. Once the coils are cooled the MRI scanners generate intense magnetic fields for a brief period of time.

22. The intense magnetic field of the MRI scanner makes the atoms inside a human body to resonate at their respective magnetic signatures. This resonance is then detected by the scanner and detailed images of internal tissues and organs are created. That is how MRI scans work.

23. There are actually 9 isotopes of Helium. 3He and 4He are the only stable ones. The other isotopes are 2He, 5He, 6He, 7He, 8He, 9He and 10He.


24. The unstable isotopes of Helium have very short half-lives. The longest half-life of the remaining unstable isotopes is that of 6 Its half-life is 806.7 milliseconds.

25. The atmosphere of our Earth has only 0.0005% of its volume as Helium.

26. Though Hydrogen is lighter than Helium, Helium is used for making things float (for example, balloon). The reason for this is that Hydrogen is high combustible and hence, dangerous.

27. It is very rare for Helium to naturally occur on our Earth. The reason is simple. It is so light that it escapes our atmosphere. The Helium that we use today is usually isolated from various other sources. Basically, Helium is found along with natural gasses and a process called fractional distillation is used for isolating Helium.

28. Using a process called liquefaction, Helium can be isolated from atmosphere but the process is too expensive to use.

29. Helium is too light and can escape our planet’s atmosphere. Then, how come it is present in our atmosphere? That’s because it is constantly replenished. There are two sources – (1) cosmic rays which contain high-energy Helium nuclei (about 9% of cosmic rays is made of Helium) and (2) radioactive decay of elements present on Earth.

30. There are two elements – Uranium and Thorium (both radioactive) present in Earth’s crust. Through α-decay, these elements release Helium. The Helium cylinders that are sold in market contain the Helium released by radioactive decay.

That concludes our list of 30 Helium facts. However, we did not write of its discovery. It is a large topic and hence, we decided to create a separate facts’ list for the same. Stay tuned to learn about discovery of Helium in our next article.

Sources: 1, 2, 3, 4, 5, 6, 7