This list includes 3 Chemical Elements that start with O, from “Oganesson” to “Oxygen”. They range from a synthetic noble gas to a life-essential gas and a dense industrial metal. Main applications include advanced research, breathing, and heavy-industry uses. See the A–Z index for the complete alphabetical list of elements.

Chemical Elements that start with O are chemical elements whose English names begin with the letter O. A notable example is oxygen, which transformed biology and industry, while Oganesson is a recent synthetic addition.

Below you’ll find the table with Atomic number, Atomic weight, Discovery year.

Atomic number: The integer shows the number of protons and helps you place the element in the periodic table quickly.

Atomic weight: The standard atomic weight (three decimals) gives you a practical mass value for comparisons and calculations.

Discovery year: The year or range indicates when the element was first identified or synthesized, giving useful historical context.

Chemical Elements that start with O

NameAtomic numberSymbolAtomic weight (u)
Oganesson118Og294.21 u (synthetic)
Osmium76Os190.23 u
Oxygen8O15.999 u

Descriptions

Oganesson
first synthesized 2002; synthetic; the heaviest known element (Z=118), extremely short-lived and produced only in particle accelerators for research (IUPAC)
Osmium
discovered 1803; natural; the densest naturally occurring element, used in very hard alloys and electrical contacts (NIST)
Oxygen
discovered 1774; natural; essential for respiration and combustion, widely used medically and in industry (steelmaking), and abundant in Earth’s atmosphere (IUPAC)
If you think there is a missing term, let us know using the contact form.