O 8

Oxygen (O)

nonmetal

Period: 2 Group: 16 Block: p

Gas

Standard Atomic Weight

Electron configuration

[He] 2s² 2p⁴

Melting point

-218.79 °C (54.36 K)

Boiling point

-182.95 °C (90.2 K)

Density

1.429 kg/m³

Oxidation states

−2, −1, 0, +1, +2

Electronegativity (Pauling)

3.44

Ionization energy (1st)

Discovery year

1771

Atomic radius

60 pm

Details

Name origin Greek: oxys and genes, (acid former).

Discovery country England/Sweden

Discoverers Joseph Priestly, Carl Wilhelm Scheele

Oxygen is a reactive nonmetal and chalcogen that occurs mainly as the diatomic gas O₂ and, less commonly, as ozone O₃. It is essential to aerobic respiration and is a major constituent of water, silicate minerals, carbonates, and many biological molecules. Its high electronegativity and ability to form strong bonds make oxidation chemistry central to combustion, corrosion, metabolism, and industrial processing.

The gas is colorless, odorless, and tasteless. The liquid and solid forms are a pale blue color and are strongly paramagnetic.

The name derives from the Greek oxys for "acid" and genes for "forming" because the French chemist Antoine-Laurent Lavoisier once thought that oxygen was integral to all acids.

Oxygen was discovered independently by the Swedish pharmacist and chemist Carl-Wilhelm Scheele in 1771, and the English clergyman and chemist Joseph Priestley in 1774. Scheele's Chemical Treatise on Air and Fire was delayed in publication until 1777, so Priestley is credited with the discovery because he published first.

Oxygen had been produced by several chemists prior to its discovery in 1774, but they failed to recognize it as a distinct element. Joseph Priestley and Carl Wilhelm Scheele both independently discovered oxygen, but Priestly is usually given credit for the discovery. They were both able to produce oxygen by heating mercuric oxide (HgO). Priestley called the gas produced in his experiments 'dephlogisticated air' and Scheele called his 'fire air'. The name oxygen was created by Antoine Lavoisier who incorrectly believed that oxygen was necessary to form all acids. Oxygen is the third most abundant element in the universe and makes up nearly 21% of the earth's atmosphere. Oxygen accounts for nearly half of the mass of the earth's crust, two thirds of the mass of the human body and nine tenths of the mass of water. Large amounts of oxygen can be extracted from liquefied air through a process known as fractional distillation. Oxygen can also be produced through the electrolysis of water or by heating potassium chlorate (KClO3).

From the Greek word oxys, acid, and genes, forming. The behavior of oxygen and nitrogen as components of air led to the advancement of the phlogiston theory of combustion, which captured the minds of chemists for a century.

Joseph Priestley is generally credited with its discovery, although Scheele also discovered it independently.

Its atomic weight was used as a standard of comparison for each of the other elements until 1961 when the International Union of Pure and Applied Chemistry adopted carbon 12 as the new basis.

Read about Oxygen on Wikipedia

Images

Properties

Physical

Atomic radius (empirical) 60 pm

Covalent radius 66 pm

Van der Waals radius 152 pm

Density

Molar volume 0.014 L/mol

Phase at STP gas

Melting point -218.79 °C

Boiling point -182.95 °C

Thermal conductivity 0.027 W/(m·K)

Specific heat capacity 0.918 J/(g·K)

Molar heat capacity 29.378 J/(mol·K)

Crystal structure cubic

Chemical

Electronegativity (Pauling) 3.44

Electronegativity (Allen) 3.61

Electron affinity

Ionization energy (1st)

Ionization energy (2nd)

Ionization energy (3rd)

Ionization energy (4th)

Ionization energy (5th)

Oxidation states −2, −1, 0, +1, +2

Valence electrons 6

Electron configuration

Electron configuration (semantic)

Thermodynamic

Triple point (temperature) -218.7916 °C

Triple point (pressure) 146.3 Pa

Critical point (temperature) -118.569 °C

Critical point (pressure) 5.043000e+6 Pa

Heat of fusion 0.00460175 eV

Heat of vaporization 0.07068456 eV

Heat of atomization 2.582474 eV

Atomization enthalpy

Nuclear

Stable isotopes 3

Discovery year 1771

Abundance

Abundance (Earth's crust) 4.610e+5 mg/kg

Abundance (ocean)

Reactivity

N/A

Crystal Structure

Lattice constant a 683 pm

Electronic Structure

Electrons per shell 2, 6

Identifiers

CAS number 7782-44-7

Term symbol

InChI InChI=1S/O

InChI Key QVGXLLKOCUKJST-UHFFFAOYSA-N

Electron Configuration Measured

Ion charge

Protons 8

Electrons 8

Charge Neutral

Configuration O: 2s² 2p⁴

[He] 2s² 2p⁴

1s² 2s² 2p⁴

Orbital diagram

↑↓

2/2

↑↓

2/2

↑↓

↑

4/6 2↑

Total electrons: 8 Unpaired: 2

Atomic model

Protons 8

Neutrons 8

Electrons 8

Mass number 16

Stability Stable

Isotopes change neutron count, mass, and stability — not the electron configuration of a neutral atom.

Schematic atomic model, not to scale.

Atomic Fingerprint

Emission / Absorption Spectrum

Emission Visible: 380–750 nm

Isotope Distribution

Mass number	Atomic mass (u)	Natural abundance	Half-life
16 Stable	15.99491461957 ± 0.00000000017	99.7570%	Stable
17 Stable	16.9991317565 ± 0.00000000069	0.0380%	Stable
18 Stable	17.99915961286 ± 0.00000000076	0.2050%	Stable

Measured

Phase / State

Gas 25 °C (298.15 K)

Reason: 207.9 °C above boiling point (-182.95 °C)

Melting point -218.79 °C

Boiling point -182.95 °C

Above boiling by 207.9 °C

0 K Current temperature: 25 °C 6000 K

Phase timeline

Schematic, not to scale

Solid

Liquid

Gas

Melting

Boiling

25°C

Solid

Liquid

Gas

Current

Phase transition points

Melting point Literature

-218.79 °C

Boiling point Literature

-182.95 °C

Current phase Calculated
Gas

Transition energies

Heat of fusion Literature

0.00460175 eV

Energy required to melt 1 mol at melting point

Heat of vaporization Literature

0.07068456 eV

Energy required to vaporize 1 mol at boiling point

Density

Reference density Literature

1.429 kg/m³

At standard conditions

Current density Estimated

0.65396019 kg/m³

Estimated via ideal gas law at current T

Advanced

Triple point Literature

-218.7916 °C

Critical point Literature

-118.569 °C

Atomic Spectra

Lines Holdings ?

Ion	Charge	Total lines	Transition probabilities	Level designations
O I	0	910	854	907
O II	+1	1630	876	1630
O III	+2	1005	974	974
O IV	+3	1525	1521	1523
O V	+4	391	385	385
O VI	+5	157	126	157
O VII	+6	189	188	189
O VIII	+7	137	137	137

NIST Lines Holdings →

Levels Holdings ?

Ion	Charge	Levels
O I	0	614
O II	+1	287
O III	+2	188
O IV	+3	219
O V	+4	172
O VI	+5	148
O VII	+6	149
O VIII	+7	149

NIST Levels Holdings →

8 O 15.9994

Oxygen — Atomic Orbital Visualizer

[He]2s22p4

Energy levels 2 6

Oxidation states -2, -1, 0, +1, +2

HOMO 2p n=2 · l=1 · m=-1

Oxygen — Atomic Orbital Visualizer Preview

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8 O 15.9994

Oxygen — Crystal Structure Visualizer

Primitive Cubic · Pearson cP1

Experimental

Pearson cP1

Coord. № 6

Packing 52.000%

No crystal structure at standard conditions — gas at 298 K, 1 atm

Solid phase structure at 293 K

Oxygen — Crystal Structure Visualizer Preview

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Ionic Radii

Charge	Coordination	Spin	Radius
-2	2	N/A	135 pm
-2	3	N/A	136 pm
-2	4	N/A	138 pm
-2	6	N/A	140 pm
-2	8	N/A	142 pm

Compounds

15.999 u

O-2

15.999 u

O-

15.999 u

O-2

17.999 u

O-2

15.003 u

Isotopes (3)

Oxygen has nine isotopes. Natural oxygen is a mixture of three isotopes.

Mass number	Atomic mass (u)	Natural abundance	Half-life	Decay mode
16 Stable	15.99491461957 ± 0.00000000017	99.7570% ± 0.0160%	Stable	stable
17 Stable	16.9991317565 ± 0.00000000069	0.0380% ± 0.0010%	Stable	stable
18 Stable	17.99915961286 ± 0.00000000076	0.2050% ± 0.0140%	Stable	stable

16 Stable

Atomic mass (u) 15.99491461957 ± 0.00000000017

Natural abundance 99.7570% ± 0.0160%

Half-life Stable

Decay mode

stable

17 Stable

Atomic mass (u) 16.9991317565 ± 0.00000000069

Natural abundance 0.0380% ± 0.0010%

Half-life Stable

Decay mode

stable

18 Stable

Atomic mass (u) 17.99915961286 ± 0.00000000076

Natural abundance 0.2050% ± 0.0140%

Half-life Stable

Decay mode

stable

Spectral Lines

Showing 50 of 1013 Spectral Lines. Only spectral lines with measured intensity are shown by default.

Wavelength (nm)	Intensity	Ion stage	Type	Transition	Accuracy	Source
615.8187 nm	490	O I	emission	2s2.2p3.(4S).3p 5P → 2s2.2p3.(4S).4d 5D*	Measured	NIST
615.6778 nm	450	O I	emission	2s2.2p3.(4S).3p 5P → 2s2.2p3.(4S).4d 5D*	Measured	NIST
700.223 nm	450	O I	emission	2s2.2p3.(4S).3p 3P → 2s2.2p3.(4S).4d 3D*	Measured	NIST
725.4448 nm	450	O I	emission	2s2.2p3.(4S).3p 3P → 2s2.2p3.(4S).5s 3S*	Measured	NIST
615.5971 nm	400	O I	emission	2s2.2p3.(4S).3p 5P → 2s2.2p3.(4S).4d 5D*	Measured	NIST
645.5977 nm	400	O I	emission	2s2.2p3.(4S).3p 5P → 2s2.2p3.(4S).5s 5S*	Measured	NIST
725.4154 nm	400	O I	emission	2s2.2p3.(4S).3p 3P → 2s2.2p3.(4S).5s 3S*	Measured	NIST
645.4444 nm	360	O I	emission	2s2.2p3.(4S).3p 5P → 2s2.2p3.(4S).5s 5S*	Measured	NIST
700.1922 nm	360	O I	emission	2s2.2p3.(4S).3p 3P → 2s2.2p3.(4S).4d 3D*	Measured	NIST
645.3602 nm	320	O I	emission	2s2.2p3.(4S).3p 5P → 2s2.2p3.(4S).5s 5S*	Measured	NIST
725.4531 nm	320	O I	emission	2s2.2p3.(4S).3p 3P → 2s2.2p3.(4S).5s 3S*	Measured	NIST
715.6701 nm	210	O I	emission	2s2.2p3.(2D).3s 1D → 2s2.2p3.(2D*).3p 1D	Measured	NIST
396.1573 nm	200	O III	emission	2s2.2p.(2P).3p 1D → 2s2.2p.(2P).3d 1F*	Measured	NIST
533.0741 nm	190	O I	emission	2s2.2p3.(4S).3p 5P → 2s2.2p3.(4S).5d 5D*	Measured	NIST
604.6438 nm	190	O I	emission	2s2.2p3.(4S).3p 3P → 2s2.2p3.(4S).6s 3S*	Measured	NIST
394.72949 nm	185	O I	emission	2s2.2p3.(4S).3s 5S → 2s2.2p3.(4S*).4p 5P	Measured	NIST
394.74813 nm	160	O I	emission	2s2.2p3.(4S).3s 5S → 2s2.2p3.(4S*).4p 5P	Measured	NIST
532.9681 nm	160	O I	emission	2s2.2p3.(4S).3p 5P → 2s2.2p3.(4S).5d 5D*	Measured	NIST
604.6233 nm	160	O I	emission	2s2.2p3.(4S).3p 3P → 2s2.2p3.(4S).6s 3S*	Measured	NIST
394.75862 nm	140	O I	emission	2s2.2p3.(4S).3s 5S → 2s2.2p3.(4S*).4p 5P	Measured	NIST
543.6862 nm	135	O I	emission	2s2.2p3.(4S).3p 5P → 2s2.2p3.(4S).6s 5S*	Measured	NIST
559.789 nm	130	O V	emission	1s2.2s.3p 3P* → 1s2.2s.3d 3D	Measured	NIST
650.024 nm	130	O V	emission	1s2.2p.(2P<3/2>).3p 3D → 1s2.2p.(2P<3/2>).3d 3F*	Measured	NIST
382.34136 nm	120	O I	emission	2s2.2p3.(2D).3s 3D → 2s2.2p3.(2P*).3p 3D	Measured	NIST
557.7339 nm	120	O I	emission	2s2.2p4 1D → 2s2.2p4 1S	Measured	NIST
543.5775 nm	110	O I	emission	2s2.2p3.(4S).3p 5P → 2s2.2p3.(4S).6s 5S*	Measured	NIST
559.2252 nm	110	O III	emission	2s2.2p.(2P).3s 1P → 2s2.2p.(2P*).3p 1P	Measured	NIST
604.6495 nm	110	O I	emission	2s2.2p3.(4S).3p 3P → 2s2.2p3.(4S).6s 3S*	Measured	NIST
395.46067 nm	100	O I	emission	2s2.2p3.(4S).3p 3P → 2s2.2p3.(2P).3s 3P*	Measured	NIST
412.396 nm	100	O V	emission	1s2.2p.(2P<3/2>).3s 3P → 1s2.2p.(2P*<3/2>).3p 3D	Measured	NIST
436.8258 nm	100	O I	emission	2s2.2p3.(4S).3s 3S → 2s2.2p3.(4S*).4p 3P	Measured	NIST
543.5178 nm	90	O I	emission	2s2.2p3.(4S).3p 5P → 2s2.2p3.(4S).6s 5S*	Measured	NIST
423.3274 nm	80	O I	emission	2s2.2p3.(4S).4p 3P → 2s2.2p3.(2D<3/2>).3d 3P*	Measured	NIST
441.4899 nm	27	O II	emission	2s2.2p2.(3P).3s 2P → 2s2.2p2.(3P).3p 2D*	Measured	NIST
672.1388 nm	26	O II	emission	2s2.2p2.(3P).3s 2P → 2s2.2p2.(3P).3p 2S*	Measured	NIST
441.6975 nm	25	O II	emission	2s2.2p2.(3P).3s 2P → 2s2.2p2.(3P).3p 2D*	Measured	NIST
397.3256 nm	24	O II	emission	2s2.2p2.(3P).3s 2P → 2s2.2p2.(3P).3p 2P*	Measured	NIST
407.58617 nm	24	O II	emission	2s2.2p2.(3P).3p 4D* → 2s2.2p2.(3P).3d 4F	Measured	NIST
464.91347 nm	24	O II	emission	2s2.2p2.(3P).3s 4P → 2s2.2p2.(3P).3p 4D*	Measured	NIST
664.1031 nm	24	O II	emission	2s2.2p2.(3P).3s 2P → 2s2.2p2.(3P).3p 2S*	Measured	NIST
407.21525 nm	23	O II	emission	2s2.2p2.(3P).3p 4D* → 2s2.2p2.(3P).3d 4F	Measured	NIST
434.9426 nm	23	O II	emission	2s2.2p2.(3P).3s 4P → 2s2.2p2.(3P).3p 4P*	Measured	NIST
411.92165 nm	22	O II	emission	2s2.2p2.(3P).3p 4P* → 2s2.2p2.(3P).3d 4D	Measured	NIST
459.0974 nm	22	O II	emission	2s2.2p2.(1D).3s 2D → 2s2.2p2.(1D).3p 2F*	Measured	NIST
464.18103 nm	22	O II	emission	2s2.2p2.(3P).3s 4P → 2s2.2p2.(3P).3p 4D*	Measured	NIST
689.5102 nm	22	O II	emission	2s2.2p2.(3P).3d 4F → 2s2.2p2.(3P).4p 4D*	Measured	NIST
406.98819 nm	21	O II	emission	2s2.2p2.(3P).3p 4D* → 2s2.2p2.(3P).3d 4F	Measured	NIST
435.126 nm	21	O II	emission	2s2.2p2.(1D).3s 2D → 2s2.2p2.(1D).3p 2D*	Measured	NIST
466.16324 nm	21	O II	emission	2s2.2p2.(3P).3s 4P → 2s2.2p2.(3P).3p 4D*	Measured	NIST
470.5346 nm	21	O II	emission	2s2.2p2.(3P).3p 2D* → 2s2.2p2.(3P).3d 2F	Measured	NIST

Extended Properties

Covalent Radii (Extended)

Covalent radius (Pyykkö)

Covalent radius (Pyykkö, double)

Covalent radius (Pyykkö, triple)

Covalent radius (Bragg)

Van der Waals Radii

Bondi

Batsanov

Alvarez

UFF

MM3

Dreiding

Rowland–Taylor

Atomic & Metallic Radii

Atomic radius (Rahm)

Numbering Scales

Mendeleev

Pettifor

Glawe

Electronegativity Scales

Ghosh

Gunnarsson–Lundqvist

Robles–Bartolotti

Polarizability & Dispersion

Dipole polarizability

Dipole polarizability (unc.)

C₆

C₆ (Gould–Bučko)

Chemical Affinity

Proton affinity

Gas basicity

Phase Transitions & Allotropes

Melting point	54.36 K
Boiling point	90.19 K
Critical point (temperature)	154.58 K
Critical point (pressure)	5.04 MPa
Triple point (temperature)	54.36 K
Triple point (pressure)	0.15 kPa

Oxidation State Categories

−2 main

+1 extended

−1 extended

+2 extended

0 extended

Advanced Reference Data

Screening Constants (3)

n	Orbital	σ
1	s	0.3421
2	p	3.5468
2	s	3.5084

Crystal Radii Detail (5)

Charge	CN	r_crystal (pm)
-2	II	121
-2	III	122
-2	IV	124
-2	VI	126
-2	VIII	128

Isotope Decay Modes (22)

Isotope	Mode	Intensity
11	2p	100%
12	2p	100%
13	B+	100%
13	B+p	10.9%
14	B+	100%
15	B+	100%
19	B-	100%
20	B-	100%
21	B-	100%
21	B-n	—

X‑ray Scattering Factors (502)

Energy (eV)	f₁	f₂
10	—	0.70328
10.1617	—	0.70723
10.3261	—	0.70738
10.4931	—	0.70753
10.6628	—	0.70768
10.8353	—	0.70783
11.0106	—	0.70798
11.1886	—	0.70813
11.3696	—	0.70828
11.5535	—	0.70843

Additional Data

Estimated Crustal Abundance

The estimated element abundance in the earth's crust.

4.61×105 milligrams per kilogram

References (1)

[5] Oxygen https://education.jlab.org/itselemental/ele008.html

Estimated Oceanic Abundance

The estimated element abundance in the earth's oceans.

8.57×105 milligrams per liter

References (1)

[5] Oxygen https://education.jlab.org/itselemental/ele008.html

Sources

Sources of this element.

Oxygen is the third most abundant element found in the sun, and it plays a part in the carbon-nitrogen cycle, the process once thought to give the sun and stars their energy. Oxygen under excited conditions is responsible for the bright red and yellow-green colors of the Aurora Borealis.

A gaseous element, oxygen forms 21% of the atmosphere by volume and is obtained by liquefaction and fractional distillation. The atmosphere of Mars contains about 0.15% oxygen. The element and its compounds make up 49.2%, by weight, of the earth's crust. About two thirds of the human body and nine tenths of water is oxygen.

In the laboratory it can be prepared by the electrolysis of water or by heating potassium chlorate with manganese dioxide as a catalyst.

References (1)

[6] Oxygen https://periodic.lanl.gov/8.shtml

Isotopes in Forensic Science and Anthropology

Information on the use of this element's isotopes in forensic science and anthropology.

Measurements of relative 18O abundances have been used to determine the breeding grounds of many species of migrant songbirds. These species of songbirds only grow their feathers before migration, and they grow them on or close to their breeding grounds. Therefore, the isotopic composition of a bird’s feathers correlates to the isotopic signature of the growing season’s precipitation [19] [19] K. A. Hobson. Oecologia120, 314 (1999).[19] K. A. Hobson. Oecologia120, 314 (1999)., [20] [20] K. A. Hobson, L. I. Wassenaar. Oecologia.109, 142 (1996).[20] K. A. Hobson, L. I. Wassenaar. Oecologia.109, 142 (1996)..

Measurements of relative 18O abundances of human hair or nail samples collected at archeological sites have been used to determine the geographic region in which a subject lived based on the oxygen isotopic composition of the water they drank (Fig. IUPAC.8.3). This is possible because hair stores a daily record of oxygen isotopic composition of intake water, which correlates to local meteoric water [92] [92] D. M. O’Brien, M. J. Woller. Rapid Commun. Mass Spectrom.21, 2422 (2007).[92] D. M. O’Brien, M. J. Woller. Rapid Commun. Mass Spectrom.21, 2422 (2007)..

References (7)

[14] W. Dansgaard. Tellus16, 436 (1964).
[15] I. D. Clark, P. Fritz. Environmental Isotopes in Hydrogeology, p. 328, Lewis Publishers, New York (1997).
[19] K. A. Hobson. Oecologia120, 314 (1999).
[20] K. A. Hobson, L. I. Wassenaar. Oecologia.109, 142 (1996).
[92] D. M. O’Brien, M. J. Woller. Rapid Commun. Mass Spectrom.21, 2422 (2007).
[93] I. Fraser, W. Meier-Augenstein, R. M. Kalin. Rapid Commun. Mass Spectrom.20, 1109 (2006).
[4] IUPAC Periodic Table of the Elements and Isotopes (IPTEI) https://doi.org/10.1515/pac-2015-0703

References

(9)

1 PubChem

Data deposited in or computed by PubChem

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2 Atomic Mass Data Center (AMDC), International Atomic Energy Agency (IAEA)

The half-life and atomic mass data was provided by the Atomic Mass Data Center at the International Atomic Energy Agency.

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3 IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW)

Oxygen

Element data are cited from the Atomic weights of the elements (an IUPAC Technical Report). The IUPAC periodic table of elements can be found at https://iupac.org/what-we-do/periodic-table-of-elements/. Additional information can be found within IUPAC publication doi:10.1515/pac-2015-0703 Copyright © 2020 International Union of Pure and Applied Chemistry.

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4 IUPAC Periodic Table of the Elements and Isotopes (IPTEI)

The information are cited from Pure Appl. Chem. 2018; 90(12): 1833-2092, https://doi.org/10.1515/pac-2015-0703.

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License note: Copyright (c) 2020 International Union of Pure and Applied Chemistry. The International Union of Pure and Applied Chemistry (IUPAC) contribution within Pubchem is provided under a CC-BY-NC-ND 4.0 license, unless otherwise stated.

5 Jefferson Lab, U.S. Department of Energy

Oxygen

Thomas Jefferson National Accelerator Facility (Jefferson Lab) is one of 17 national laboratories funded by the U.S. Department of Energy. The lab's primary mission is to conduct basic research of the atom's nucleus using the lab's unique particle accelerator, known as the Continuous Electron Beam Accelerator Facility (CEBAF). For more information visit https://www.jlab.org/

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License note: Please see citation and linking information: https://education.jlab.org/faq/index.html

6 Los Alamos National Laboratory, U.S. Department of Energy

Oxygen

The periodic table at the LANL (Los Alamos National Laboratory) contains basic element information together with the history, source, properties, use, handling and more. The provenance data may be found from the link under the source name.

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7 NIST Physical Measurement Laboratory

Oxygen

The periodic table contains NIST's critically-evaluated data on atomic properties of the elements. The provenance data that include data for atomic spectroscopy, X-ray and gamma ray, radiation dosimetry, nuclear physics, and condensed matter physics may be found from the link under the source name. Ref: https://www.nist.gov/pml/atomic-spectra-database

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8 PubChem Elements

Oxygen

This section provides all form of data related to element Oxygen.

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9 PubChem Elements

Oxygen

The element property data was retrieved from publications.

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Last updated: May 1, 2026

Data verified: May 12, 2026

Content is reviewed against latest scientific data.