Carbon at a glance
- Atomic number
- 6
- Symbol
- C
- Atomic mass
- 12.011 u
- Category
- Reactive nonmetal
- Group / period
- 14 / 2
- Electron configuration
- [He] 2s 2 2p 2
- State at 25 °C
- Solid
- Melting point
- 3550 °C
- Boiling point
- 3825 °C
- Density
- 2.267 g/cm³
- Electronegativity
- 2.55
- 1st ionization energy
- 1086 kJ/mol
- Oxidation states
- +4, +2, −4
- Discovered
- Antiquity
Atomic structure
A neutral carbon atom has 6 protons and 6 electrons, and its most common isotope carries about 6 neutrons. One atom weighs about 1.99 × 10⁻²⁶ kg, so a mole of carbon (6.022 × 10²³ atoms) weighs 12.011 g. That nucleus holds 1 neutrons for every proton, close to the one-to-one balance that light nuclei prefer. The electrons fill 2 shells (K 2, L 4), which gives the configuration [He] 2s 2 2p 2. With 4 electrons in its outer shell, it usually shares electrons in covalent bonds. It has 2 stable isotopes: C-12 and C-13. No other element has a stable isotope with mass number 12, so C-12 has no stable isobars; its neighbours on that line decay into it or away from it.
Physical properties
At room temperature (25 °C) carbon is a solid. It melts at 3550 °C and boils at 3825 °C, so it stays liquid across a 275-degree range. It stays solid in a welding arc but would melt in the surface of the Sun. That is the 1st highest melting point of any element. Its density is 2.267 g/cm³, 2.27 times as dense as water. Its atoms have a radius of about 70 pm (Boron next door is 85 pm). In the solid, its atoms pack into a layered hexagonal lattice.
Chemical behaviour
Its electronegativity is 2.55 on the Pauling scale. Pulling off its outermost electron takes 1086 kJ/mol. A bond between carbon and chlorine would be polar covalent, with an electronegativity difference of 0.61. It releases 122 kJ/mol when it gains an extra electron. Its common oxidation states are +4, +2, −4, so in compounds you will usually meet it as C⁴⁺, C²⁺ and C⁴⁻. Group 14 also holds Silicon, Germanium, Tin, Lead and Flerovium, which share its outer-shell pattern. Its Lewis symbol is C surrounded by 4 dots.
Where it comes from
It makes up 200 mg/kg of Earth's crust, the 17th most abundant element there. In the human body it accounts for about 18.5 % of body mass, making it one of the main building blocks of life. It has been known since ancient times, one of only 11 elements people used before modern chemistry.