Oxygen (O): electron configuration, atomic mass and facts
Oxygen (O) is element 8 of the periodic table, a reactive nonmetal in period 2, group 16. Its electron configuration is [He] 2s2 2p4, with electrons arranged in shells 2, 6, and its standard atomic weight is 15.999 u.
💡 About 21% of air. Needed for burning and for respiration.
▶ Watch Oxygen’s electrons orbit in the interactive periodic tableOxygen at a glance
| Symbol | O |
|---|---|
| Atomic number | 8 |
| Atomic mass | 15.999 u |
| Category | Reactive nonmetal |
| Group | 16 |
| Period | 2 |
| Block | p-block |
| Electron configuration | 1s2 2s2 2p4 |
| Noble-gas shorthand | [He] 2s2 2p4 |
| Electrons per shell | 2, 6 |
| Outer-shell electrons | 6 |
| Electronegativity (Pauling) | 3.44 |
| State at 20 °C | gas |
Experiments with oxygen
🧪 Acid–base titration
Find the end-point of HCl vs NaOH with phenolphthalein and plot the titration curve.
🐘 Elephant's toothpaste
Iodide-catalysed decomposition of 30% hydrogen peroxide produces a towering, steaming foam.
🔥 Preparing oxygen
Heat potassium permanganate, pipe the gas into a gas jar and confirm with a glowing splint.
🫧 CO₂ and limewater
Marble + acid makes CO₂. Bubble it through limewater: milky, then clear again in excess.
Where is Oxygen on the periodic table?
Oxygen is in period 2, group 16, in the p-block. The period number matches its 2 electron shells, and the block names the subshell its last electrons fill. In the same group, Sulfur sits directly below it. Elements in one group have the same number of outer-shell electrons (6 here), which is why they react in similar ways.
How to work out the electron configuration of Oxygen
Put 8 electrons into subshells in order of rising energy, filling each before starting the next: 1s² (2), 2s² (4), 2p⁴ (8). In shorthand, [He] stands for the 2 electrons of helium, giving [He] 2s² 2p⁴.
How electronegative is Oxygen?
Oxygen has a Pauling electronegativity of 3.44, ranking 2 of the 100 elements with a known value (fluorine is highest at 3.98). That is high: it pulls shared electrons strongly towards itself in a bond.
Oxygen in the virtual lab
Faradium’s chemistry workbench includes these chemicals that contain oxygen: Marble chips, Sodium carbonate, Baking soda, Potassium nitrate, Sodium hydroxide pellets, Quicklime, Slaked lime, Ammonium nitrate, Copper sulfate crystals, Anhydrous copper sulfate, Iron(II) sulfate crystals, Aluminium sulfate, Potassium permanganate, Potassium chlorate, Manganese dioxide, Copper(II) oxide, Iron(III) oxide, Malachite, Mercury(II) oxide, Sugar (sucrose), Distilled water, Dilute sulfuric acid, Conc. sulfuric acid, Dilute nitric acid, Conc. nitric acid, Ethanoic acid (vinegar), Sodium hydroxide, Sodium hydroxide 0.1 M, Potassium hydroxide, Limewater, Barium hydroxide, Magnesium sulfate, Silver nitrate, Lead(II) nitrate, Copper(II) sulfate, Iron(II) sulfate, Zinc sulfate, Sodium hydrogencarbonate, Sodium sulfate, Sodium sulfite, Sodium thiosulfate, Potassium dichromate, Hydrogen peroxide 6%, Hydrogen peroxide 30%, Ethanol, Oxygen cylinder, Carbon dioxide cylinder, Sulfur dioxide. Open the Chemistry Lab to experiment with them.
Frequently asked questions
What is the electron configuration of Oxygen?
The electron configuration of Oxygen (O) is 1s2 2s2 2p4. In noble-gas shorthand it is written [He] 2s2 2p4.
How many electrons does Oxygen have in each shell?
Oxygen has 8 electrons arranged in shells as 2, 6. It has 6 electrons in its outer shell.
What is the atomic mass of Oxygen?
The standard atomic weight of Oxygen is 15.999 u, so one mole of Oxygen atoms has a mass of about 15.999 g.
Is Oxygen a metal?
No. Oxygen is a reactive nonmetal.
Explore nearby elements
More reactive nonmetals: Hydrogen, Carbon, Nitrogen, Phosphorus, Sulfur, Selenium. See all elements on the periodic table.