Atomic Number 8 Element Facts

What Element is Atomic Number 8?

Oxygen is atomic number 8 on the periodic table. Each oxygen atom has 8 protons.
Oxygen is atomic number 8 on the periodic table. Each oxygen atom has 8 protons. ROGER HARRIS/SCIENCE PHOTO LIBRARY / Getty Images

Oxygen, element symbol O, is the element that is atomic number 8 on the periodic table. This means every atom of oxygen has 8 protons. Varying the number of electrons forms ions, while altering the number of neutrons makes different isotopes of the element, but the number of protons remains constant. Here is a collection of interesting facts about atomic number 8.

Atomic Number 8 Element Facts

  • While oxygen is a colorless gas under ordinary conditions, element 8 is actually quite colorful! Liquid oxygen is blue, while the solid element may be blue, pink, orange, red, black, or even metallic.
  • Oxygen is a nonmetal belonging to the chalcogen group. It is highly reactive and readily forms compounds with other elements. It is found as a pure element in nature as oxygen gas (O2) and ozone (O3). Tetraoxygen (O4) was discovered in 2001. Tetraoxygen is an even more potent oxidizer than dioxygen or trioxygen.
  • Excited oxygen atoms produce the green and red colors of the aurora. Although air consists mainly of nitrogen, atomic number 8 is responsible for most of the colors that we see.
  • Today, oxygen makes up about 21% of the Earth's atmosphere. However, air was not always so highly oxygenated! A 2007 NASA-funded study determined oxygen has been present in air for about 2.3 billion to 2.4 billion years, with levels starting to rise 2.5 billion years ago. Photosynthetic organisms, such as plants and algae, are responsible for maintaining the high oxygen levels necessary for life. Without photosynthesis, oxygen levels in the atmosphere would fall.
  • Although hydrogen atoms are the most numerous type of atom in the human body, oxygen accounts for about two-thirds of the mass of most living organisms, mainly because cells contain a lot of water. 88.9% of the weight of water comes from oxygen.
  • Swedish pharmacist Carl Wilhelm Scheele, French chemist Antoine Laurent Lavoisier, and British scientists and clergyman Joseph Priestly researched and discovered oxygen between 1770 and 1780. Lavoisier first called element number 8 by the name "oxygen" in 1777.
  • Oxygen is the third most abundant element in the universe. The element is made by stars around 5x more massive than the Sun when they reach the point where they burn carbon or a combination of helium in carbon in fusion reactions. Over time, the abundance of oxygen in the universe will increase.
  • Until 1961, atomic number 8 was the standard for the atomic weight of the chemical elements. In 1961, the standard was switched over to carbon-12.
  • It's a common misconception that hyperventilation is caused by breathing in too much oxygen. Actually, hyperventilating is caused by exhaling too much carbon dioxide. Although carbon dioxide can be toxic at high levels, its needed in the blood to prevent it from becoming too alkaline. Breathing too quickly causes blood pH to rise, which constricts blood vessels in the brain, leading to headache, slurred speech, dizziness, and other symptoms.
  • Oxygen has many uses. It is used for oxygen therapy and life support systems. It is a common oxidizer and propellant for rockets, welding, cutting, and brazing. Oxygen is used in internal combustion engines. Ozone functions as a natural planetary radiation shield.
  • Pure oxygen is not, in fact, flammable. It is an oxidizer, supporting combustion of flammable materials.
  • Oxygen is paramagnetic. In order words, oxygen is only weakly attracted to a magnet and does not maintain permanent magnetism.
  • Cold water can hold more dissolved oxygen than warm water. The polar oceans contain more dissolved oxygen than equatorial or mid-latitude oceans.

Essential Element 8 Information

Element Symbol: O

State of Matter at Room Temperature: Gas

Atomic Weight: 15.9994

Density: 0.001429 grams per cubic centimeter

Isotopes: At least 11 isotopes of oxygen exist. 3 are stable.

Most Common Isotope: Oxygen-16 (accounts for 99.757% of the natural abundance)

Melting Point: -218.79 °C

Boiling Point: -182.95 °C

Triple Point: 54.361 K, ​0.1463 kPa

Oxidation States: 2, 1, -1, 2

Electronegativity: 3.44 (Pauling scale)

Ionization Energies: 1st: 1313.9 kJ/mol, 2nd: 3388.3 kJ/mol, 3rd: 5300.5 kJ/mol

Covalent Radius: 66 +/- 2 pm

Van der Waals Radius: 152 pm

Crystal Structure: Cubic

Magnetic Ordering: Paramagnetic

Discovery: Carl Wilhelm Scheele (1771)

Named By: Antoine Lavoisier (1777)

Further Reading

  • Cacace, Fulvio; de Petris, Giulia; Troiani, Anna (2001). "Experimental Detection of Tetraoxygen". Angewandte Chemie International Edition. 40 (21): 4062–65.
  • Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann.
  • Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing.