8 O Oxygen 15.999 u

Oxygen

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Period
2
Group
16
Block
p-block
Phase (STP)
Gas

Oxygen is the third most abundant element in the universe and essential for respiration. It makes up about 21% of Earth's atmosphere.

Appearance: Colorless gas (pale blue as liquid)

About Oxygen

Essential to the respiration of most living organisms, oxygen is a colorless, reactive nonmetal that makes up about 21 percent of the atmosphere and ranks as the third most abundant element in the universe. It bears atomic number 8 and an atomic mass of 15.999, condensing to a pale blue liquid at 90 K. Six valence electrons ([He] 2s2 2p4) and an electronegativity of 3.44—second only to fluorine—drive its tendency to form oxides with nearly every other element; its first ionization energy is 1314 kJ/mol. Carl Wilhelm Scheele prepared the gas around 1771. Oxygen occupies group 16, period 2, at the top of its group.

Physical Properties

Atomic Mass 15.999 u
Density 0.001429 g/cm³
Melting Point -218.8 °C
Boiling Point -183.0 °C
Phase at STP Gas
Atomic Radius 73.0 pm

Electronic Properties

Electronegativity 3.44
Ionization Energy 1313.9 eV
Electron Affinity 141.0 eV
Valence Electrons 6

Electron Configuration

Configuration [He] 2s² 2p⁴

Electron Shell Configuration

Oxygen electron shell configuration O 2e⁻ 6e⁻
Electron shell structure of Oxygen — electrons per shell.
Shell Electrons
1 (K) 2
2 (L) 6

Position in Periodic Table

Oxygen position in the periodic table O

Discovery

Discovered by: Carl Wilhelm Scheele
Year: 1771

Block & Period

Block

s p d f

Period

1 2 3 4 5 6 7

Periodic Table

Lanthanides Actinides

Reactions Involving O

Aluminum Reacting with Iron(III) Oxide (Thermite)

2Al + Fe₂O₃ → Al₂O₃ + 2Fe

Single-Replacement

Aqua Regia Dissolving Gold

Au + 3HCl + HNO₃ → HAuCl₄ + NO + 2H₂O

Redox

Barium Sulfate Precipitation

BaCl₂ + Na₂SO₄ → BaSO₄↓ + 2NaCl

Precipitation

Carbonic Acid Dissociation (Blood Buffer)

H₂CO₃ ⇌ HCO₃⁻ + H⁺

Acid-Base

Carbon Reducing Iron Oxide in Blast Furnace

2Fe₂O₃ + 3C → 4Fe + 3CO₂

Single-Replacement
View all 261 reactions →

Compounds Containing Oxygen

1,4-Dioxane

C₄H₈O₂

1-Butanol

C₄H₁₀O

2-Propanol

C₃H₈O

Acetaldehyde

CH₃CHO

Acetamide

C₂H₅NO

Acetic Acid

CH₃COOH

Acetic Anhydride

C₄H₆O₃

Acetone

(CH₃)₂CO

Acrolein

C₃H₄O

Acrylamide

C₃H₅NO

Acrylic Acid

C₃H₄O₂

Adenosine Triphosphate

C₁₀H₁₆N₅O₁₃P₃

More Nonmetal

1 H Hydrogen 6 C Carbon 7 N Nitrogen 15 P Phosphorus 16 S Sulfur 34 Se Selenium

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Frequently Asked Questions

What is Oxygen?
Oxygen (O) is a chemical element with atomic number 8. It is a gas at standard temperature and pressure, classified as a nonmetal.
What are the key properties of Oxygen?
Oxygen has an atomic mass of 15.999 u, density of 0.001429 g/cm³, melting point of -218.8°C, boiling point of -183.0°C.
What is the electron configuration of Oxygen?
The electron configuration of Oxygen is [He] 2s2 2p4. It is in the p-block of the periodic table.
Who discovered Oxygen?
Oxygen was discovered by Carl Wilhelm Scheele in 1771.
What is the electronegativity of Oxygen?
Oxygen has an electronegativity of 3.44 on the Pauling scale.