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What Is the Difference Between Helium & Nitrogen?

Helium and nitrogen have a lot in common: both are tasteless, odorless, nontoxic and generally unreactive, and both are gases at room temperature and pressure. However, they do have some very important differences in their atomic and physical properties, which arise from the difference in the number of protons in the nucleus -- the very thing that makes an atom a particular element.

Nuclei
- At the center of an atom is a nucleus containing positively charged protons and uncharged neutrons. Surrounding and orbiting the positively charged nucleus are negatively charged electrons, which are electrostatically attracted to the nucleus because of their opposite electrical charges. In helium atoms, the nucleus contains two protons and usually two neutrons. However, in nitrogen, the nucleus contains seven protons and usually seven neutrons. For a particular element, the number of protons is always the same, but the number of neutrons can vary and determines the isotope.
Electrons
- The number of electrons in an atom is equal to the number of protons in the nucleus. Therefore, helium has two electrons per atom, but nitrogen has seven electrons per atom. Helium is a noble gas because its most outer -- and only -- shell of electrons is full, containing two out of two possible electrons. In contrast, nitrogen is a nonmetal because its most outer shell is unfilled, containing five out of eight possible electrons.
Bonding
- The differences in the occupation of the electron shells lead to differences in the bonding between atoms of helium and nitrogen. In the case of helium, no bonding between helium atoms is observed because its most outer shell is full and the addition of more electrons would be energetically unfavorable. On the other hand, nitrogen exists as a diatomic molecule because each atom of nitrogen has an incomplete outer shell of electrons. The formation of a triple covalent bond between two nitrogen atoms enables atoms to complete their outer shell of eight electrons by sharing six electrons between them.
Boiling and Melting Points
- The boiling point of nitrogen is -195.79 degrees Celsius, which is 73.14 degrees higher than the boiling point of helium, at -268.93 degrees Celsius. The melting point of nitrogen is -210.1 degrees Celsius, but helium does not even solidify at atmospheric pressure. This difference is caused by the differences in interactions between helium atoms and nitrogen molecules, which are very weak in helium and slightly stronger in nitrogen.

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