Hydrogen vs Helium
Hydrogen and helium are the first two elements in the periodic table. Both are gases and have a high abundance in the universe. They are very simple elements having electrons filled to 1s orbital only. Hydrogen only has one electron and by obtaining another one it can achieve the electron configuration of Helium.
Hydrogen
Hydrogen is the first and the smallest element in the periodic table which is denoted as H. It has one electron and one proton. It is categorized under group 1 and period 1 in the periodic table because of its electron configuration: 1s1. Hydrogen can take up an electron to form a negatively charged ion, or can easily donate the electron to produce a positively charged proton or share the electron to make covalent bonds. Because of this ability, hydrogen is present in a large number of molecules, and it is a highly abundant element in earth. Hydrogen has three isotopes named as protium-1H (no neutrons), deuterium-2H (one neutron), and tritium- 3H (two neutrons). Protium is the most abundant among three having about 99% relative abundance. Hydrogen exists as a diatomic molecule (H2) in the gas phase, and it is a colorless, odorless gas. Furthermore, hydrogen is an extremely flammable gas and it burns with a pale blue flame. Under normal room temperature hydrogen is not very reactive. However, in high temperatures it can react fast. H2 is in the zero oxidation state, therefore, it can act as a reducing agent to reduce metal oxides, or chlorides and release metals. Hydrogen is used in chemical industries such as for ammonia production in Haber process. Liquid hydrogen is used as a fuel in rockets and vehicles.
Helium
Helium is the second element in the periodic table, and it is in the group 18 (Nobel gas). It has two electrons; therefore, the electron configuration is 1s2. S orbital can only accommodate two electrons, so in helium s orbital is fully filled making helium an inert gas. He is the symbol of helium, and its molecular weight is 4 g mol-1. Helium is a light, colorless, odorless gas like hydrogen. It also has a low boiling point, low density, low solubility and high thermal conductivity. The melting point (0.95 K) and the boiling point (4.22 K) of helium are considered as the lowest values among other elements. Helium has seven isotopes, among those only He-3 and He-4 are stable. Helium is lighter than air, so it is used to fill balloons, airships. Further it is used for magnetic resonance imaging (MRI), for pressurizing liquid fuel rockets, as a cooling medium for nuclear reactors, etc.
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What is the difference between Hydrogen and Helium – Hydrogen is a diatomic gas, and helium is a monatomic gas. – Helium has a fully filled s orbital (1s2), but in hydrogen, there is only one electron (1s1), so it is unstable. – Compared to hydrogen, helium is an inert gas. – Helium is lighter than air, but hydrogen is slightly heavier than air. – Hydrogen is reactive compared to helium so hydrogen form many chemical compounds but helium doesn’t. -Hydrogen is extremely flammable, helium is non flammable. – Hydrogen has a higher boiling point compared to that of helium. – There are seven isotopes of helium, but for hydrogen, there are only three naturally occurring isotopes.
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Hydrogen and Helium are both lighter than air. (The yellow box filled with differences is wrong.)