Helium Element in Periodic Table | Atomic Number Atomic Mass
Helium is an inert gas which is the simplest and foremost compound in the group of inert gases. It has two protons and two electrons in its nucleus. Hence its mass number is four (the total number protons and neutrons, collectively called nucleons). There are two electrons which rotate around the nucleus of helium. The number of protons is called the atomic number of any element. Since there are two protons in the nucleus of helium, the atomic number of helium is two. The orbital in which two electrons are present is called s-orbital. The maximum accommodating capacity of s-orbital is two electrons. Since the orbital of helium is completely filled, helium atom is in a saturated state which makes it unreactive with other elements. Hence, helium is grouped in the list of inert gases. The number of inert gas group is 18 in the modern periodic table. Since other inert gases have higher atomic number than helium, they are placed in the successive lower positions in the inert gases group. Inert gases are also called noble gases.
The electronic configuration of inert gases is taken as the criterion for an atom other reactive elements to participate in chemical reaction to attain stable configuration. To elaborate more lucidly, an atom while undergoing chemical reaction tends to gain or lose electrons to attain the stable configuration of inert gas present in the same period of periodic table. The tendency for attaining stable electronic configuration is cited as the main reason for explaining the reactivity of an element in periodic table.
The symbol of helium is He. Unlike hydrogen which has two atoms in a single molecule, helium is a monoatomic element which means a single atom of He itself exists as a molecule.
He is a colorless, odorless, tasteless, non-poisonous monoatomic inert gas. It is the second most abundant element, after hydrogen, in the observable extent of universe. Like hydrogen, the formation of He is also found out to be the immediate effect of Big Bang. It is formed due to nuclear fusion of highly active hydrogen atoms in plasma state in the atmosphere of sun and stars.
He is the second least reactive gas after neon, its immediate successor in the inert gas group of periodic table. Since helium has the second lowest atomic mass after hydrogen, its thermal conductivity, specific heat and sound speed in gas phase are all greater than any element except hydrogen. Due to the small size of monoatomic molecule, the rate of diffusion through solids is three more than that of air and 65% of that of hydrogen.
"He" is in liquid state below the absolute temperature under normal pressure.
Although there are nine isotopes of helium, the stable ones among them are two isotopes called helium-3 and helium-4. The ratio of abundance of helium-3 and helium-4 is that for every one million atoms of helium-4, a single atom of helium-3 is found on earth. But in interstellar medium, the relative presence of helium-3 with respect to helium-4 is hundred times more than that on earth.
Under normal conditions, neutral helium is non-poisonous and harmless gas. However, when He is inhaled in excess quantities it may result in asphyxiation or troubled respiration because He replaces oxygen necessary proper respiration. When the medium of air and the medium of He are compared, the speed of sound in helium gas is three times more than that in air.
Uses of Helium Element:
- in medical observance of respiratory mechanism while treating asthma, emphysema and other conditions that interfere breathing ;
- in cooling down super conducting magnets ;
- in preparation of helium balloons ;
- In preparing helium-and-air mixture in the cylinders used by scuba divers ;
- As a medium of atmosphere for manufacturing cables (for internet and television) for avoiding air bubbles getting trapped inside the cables ;
- In cleaning the emptied rocket-fuel tanks after liquid hydrogen and liquid oxygen are completely used up ;
- As a cooling medium at about -271.3 ̊C in LHC (Large Hadron Collider) to avoid overheating during bombardment by atomic particles in a 17-mile long tunnel underground ;
- In arc welding as a shielding gas.
Helium Element Information:
Discovery year: 1868
Discovered by: Pierre Janssen, Norman Lockyer
Atomic number: 2
Relative atomic mass: 4.002602 u ± 0.000002 u
Electron configuration: 1s2
Other elements in the same block
Period: Period 1
Other elements in the same period
Hydrogen is the element in the same period.
Group: group 18 (noble gases)
Other elements in the same group
Other elements in the same orbital
Hydrogen is the element in the same orbital.
Key isotopes: 4He
Melting point: 0.95 K (−272.20 °C, −457.96 °F) (at 2.5 MPa)
Boiling point: 4.222 K (−268.928 °C, −452.070 °F)
Element category: noble gas
Density (g cm−3): 0.000164
CAS number: 7440-59-7
Color: Colorless gas
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