Oxygen

Oxygen is atom number 8 — every Oxygen atom has exactly 8 protons in its center, and that number is what makes it Oxygen and nothing else. Its symbol is O. At room temperature it is a gas.

Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table and is a highly reactive nonmetal and oxidizing agent that readily forms compounds (notably oxides) with most elements. By mass, oxygen is the third-most abundant element in the universe, after hydrogen and helium.

Summary from the source dataset, derived from Wikipedia (CC BY-SA 3.0) · original article

Oxygen sits in period 2, group 16 of the p-block. Its 8 electrons fill shells of 2, 6 — written as [He] 2s2 2p4. Its electronegativity is 3.44 on the Pauling scale, and pulling the first electron off takes 1313.9 kJ/mol. The outermost shell holds 6 electrons — the ones that do all the chemistry.

Full configuration: 1s2 2s2 2p4
Ionization energies (kJ/mol): 1313.9, 3388.3, 5300.5, 7469.2, 10989.5, 13326.5, 71330, 84078
Electron affinity: 140.976 kJ/mol · Electronegativity (Pauling): 3.44
Density: 1.429 g/L · melts 54.36 K · boils 90.188 K

Values exactly as published — see where the data comes from.