Difference Between Hydrogen and Oxygen

Main Difference – Hydrogen vs Oxygen

The periodic table of elements shows each and every element that has been so far discovered on the earth according to their atomic numbers (ascending order). Some of these elements are very abundant on earth whereas other elements are found in trace amounts. Hydrogen and Oxygen are two elements that are found almost everywhere on earth. The main difference between Hydrogen and Oxygen is that Hydrogen has no neutrons in its most stable isotope whereas Oxygen has 8 neutrons in its most stable isotope.

Key Areas Covered

1. What is Hydrogen
     – Definition, Isotopes, Structure, Properties, Abundance
2. What is Oxygen
      – Definition, Isotopes, Structure, Properties, Abundance
3. What is the Difference Between Hydrogen and Oxygen
      – Comparison of Key Differences

Key Terms: Allotropes, Atomic Number, Electron, Hydrogen, Isotopes, Neutron, Oxygen, Proton, ProtiumDifference Between Hydrogen and Oxygen - Comparison Summary

What is Hydrogen

Hydrogen is an element with atomic number 1 and symbol H. It is the element that is found in the top of the periodic table. Hydrogen has three naturally occurring isotopes. They are protium, deuterium, and tritium. They differ from each other in the number of neutrons they have in their nucleus. Among these isotopes, the most commonly found isotope is protium. The abundance of protium in nature is about 98%. Therefore, the term Hydrogen typically refers to Protium.

Hydrogen has no neutrons, only one proton, and one electron. Hydrogen has only one s orbital and no other orbitals. Therefore, the only electron that Hydrogen atom has is in located in s orbital. Since this electron is alone and unpaired, Hydrogen can form H+ ion easily by removing this electron. The presence of an unpaired electron makes the Hydrogen atom unstable. Therefore, Hydrogen tends to form covalent bonds with many different elements by sharing its electron with them.

The most common form of Hydrogen that is found in nature is water molecules. Two Hydrogen atoms are bonded covalently with one oxygen atom in a water molecule. The molecular formula of water is given as H2O. Apart from that, Hydrogen is found in hydrocarbons, many common polymers and other organic and inorganic species. Hydrogen is found in the atmosphere as Hydrogen gas. The molecular formula of Hydrogen gas is H2. There, two Hydrogen atoms are connected through a covalent bond by sharing the only electron they have.

Main Difference - Hydrogen vs Oxygen

Figure 01:  Chemical Structure of H and H2

At standard temperature and pressure, Hydrogen is a colorless, odorless and non-toxic gas. It is highly flammable. When H2 gas reacts with metal elements, it forms the Hanion. This anion is called hydride. The bond between metal and hydride is ionic, and Hydrogen atom has two electrons (paired) in hydride anion.

What is Oxygen

Oxygen is an element with atomic number 8 and symbol O. The naturally occurring Oxygen has three isotopes. They are 16O, 17O and 18O. But the most abundant form is 16O. Therefore, when we generally talk about oxygen, we are referring to 16O isotope.

Oxygen has 8 protons and 8 neutrons in its nucleus. It also has 8 electrons around the nucleus. These electrons are in s and p orbitals. The electron configuration of Oxygen is 1s22s22p4. As the outermost orbital containing electrons is p orbital, Oxygen belongs to the p block of the periodic table. Oxygen has 4 electrons in the 2p orbital. Two of them are paired, and other two electrons are unpaired. Therefore, oxygen can make O2- anion by obtaining two electrons from outside. When two electrons are gained, oxygen gets the electron configuration of Neon, which is a very stable configuration.

Oxygen forms O2 gas. It is the gas which every living being needs for their respiration. The percentage of O2 gas in the atmosphere is about 21%. Therefore, oxygen is most abundantly found in the atmosphere. Oxygen is also found as a part of water molecules. There, the oxygen atom is attached with two Hydrogen atoms through covalent bonds. Oxygen is the second most electronegative element and is second only to Fluorine.

Difference Between Hydrogen and Oxygen

Figure 02: Formation of O2 Molecule

At standard temperature and pressure, oxygen occurs as a diatomic molecule that is odorless, colorless and non-toxic. There are two allotropes of oxygen as O2 and O3. O2 is typically called dioxygen or oxygen whereas O3 is called ozone. Ozone is mainly found in the ozone layer in the upper atmosphere.

Difference Between Hydrogen and Oxygen


Hydrogen: Hydrogen is an element with atomic number 1 and symbol H.

Oxygen: Oxygen is an element with atomic number 8 and symbol O.

Number of Neutrons

Hydrogen: The most common isotope of Hydrogen has no neutrons in its nucleus.

Oxygen: The most common isotope of Oxygen has 8 neutrons in its nucleus.


Hydrogen: Hydrogen has only one s orbital.

Oxygen: Oxygen has s and p orbitals.

Number of Unpaired Electrons

Hydrogen: Hydrogen has one unpaired electron.

Oxygen: Oxygen has two unpaired electrons.

Number of Covalent Bonds

Hydrogen: Hydrogen can form only one covalent bond.

Oxygen: Oxygen can form two covalent bonds.

Atomic Mass

Hydrogen: The atomic mass of Hydrogen is about 1.00794 u.

Oxygen: The atomic mass of Oxygen is 15.999 u.


Both Hydrogen and Oxygen are very abundant in earth’s crust. Therefore, it is important to understand the difference between Hydrogen and Oxygen. These elements are found either in the gaseous phase as their diatomic molecules or as solid or liquid phases when bonded with other elements.


1.”Canadian Hydrogen and Fuel Cell Association.” What is Hydrogen? N.p., n.d. Web. . 07 July 2017. 
2.”What is Oxygen?” Inogen. N.p., n.d. Web. . 07 July 2017. 

Image Courtesy:

1. “Covalent bond hydrogen” By Jacek FH – Own work via
2. “Figure 02 01 09″ By via

About the Author: Madhusha

Madhusha is a BSc (Hons) graduate in the field of Biological Sciences and is currently pursuing for her Masters in Industrial and Environmental Chemistry. Her interest areas for writing and research include Biochemistry and Environmental Chemistry.

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