Carbon
Atomic Data
| Atomic Number | 6 |
| Symbol | C |
| Atomic Weight | 12.011 u |
| Density (STP) | 2.267 g/cm³ |
| Melting Point | 3549.85 °C (3823 K) |
| Boiling Point | 3824.85 °C (4098 K) |
| Electronegativity | 2.55 (Pauling) |
| Electron Config. | 1s² 2s² 2p² |
| Oxidation States | +4, +2, −4 |
| Phase at STP | Solid |
| Category | Reactive nonmetal |
| Period / Group | 2 / 14 |
| CAS Number | 7440-44-0 |
Electron Configuration
1s2 2s2 2p2
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 2 | 6 |
| Total | 4 | 6 | ||
Isotopes of Carbon
Carbon has two stable isotopes: carbon-12, the most abundant at 98.93%, and carbon-13 at 1.07%. Carbon-12 defines the atomic mass unit. Carbon-14, produced in the upper atmosphere by cosmic rays, is radioactive with a half-life of 5,730 years and is the basis of radiocarbon dating.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Carbon-12 | ²¹C | 6 | 6 | 98.93% | Stable |
| Carbon-13 | ¹³C | 6 | 7 | 1.07% | Stable |
| Carbon-14 | ¹⁴C | 6 | 8 | Trace | Radioactive (t½ = 5730 yr) |
Abundance & Occurrence
Carbon is the fourth most abundant element in the universe by mass (after hydrogen, helium, and oxygen), present at about 5,000 ppm. In Earth's crust it is less dominant at roughly 200 ppm, but it is the defining element of organic chemistry and the biosphere. Carbon occurs as free mineral carbon (diamond and graphite), as carbonate rocks (limestone, dolomite), in fossil fuels (coal, oil, natural gas), dissolved as CO2 in the oceans, and as the building block of all living organisms.
Composition of the Universe By Mass (%)
Human Body Composition By Mass (%)
Discovery & History
Safety & Handling
- Elemental carbon is generally non-toxic: Diamond, graphite, and activated carbon are considered biologically inert and are not classified as hazardous. Activated carbon is even used medically as an adsorbent for poison treatment.
- Fine carbon black dust — respiratory hazard: Prolonged inhalation of very fine carbon black particles (a form of amorphous carbon used in tyres and inks) may cause respiratory irritation. Carbon black is classified by the IARC as a Group 2B possible human carcinogen based on occupational exposure studies.
- Carbon monoxide (CO) — severe toxicity: CO binds to haemoglobin with ~250× the affinity of oxygen, causing rapid asphyxiation. It is colourless and odourless — the leading cause of accidental poisoning deaths in the developed world. Carbon monoxide detectors are essential wherever combustion occurs indoors.
- Carbon dioxide (CO2) — asphyxiant at high concentrations: CO2 is non-toxic at atmospheric levels but is an asphyxiant above ~5% concentration, causing unconsciousness and death. Risk areas include confined spaces near fermentation, dry ice storage, and CO2 extinguisher use.
- Carbon nanotubes — potential hazard under study: Some forms of carbon nanotubes (particularly long, rigid, biopersistent fibres) may cause asbestos-like pathology. Standard precautions for nanomaterial handling apply.
Carbon in the Real World
Real-World Uses
- Steel production — Carbon is the defining additive in steel: iron with 0.02–2.1% carbon by mass is steel. Higher carbon content increases hardness and strength but reduces ductility. Carbon is added via coke (a purified coal product) in the blast furnace steelmaking process, which produces over 1.8 billion tonnes of steel per year worldwide.
- Fossil fuels — Coal, petroleum, and natural gas are all carbon-based fuels formed from ancient organic matter. They supply roughly 80% of world primary energy, powering electricity generation, transportation, heating, and industrial processes.
- Diamond tooling — Industrial diamonds (mostly synthetic) are the hardest known material, used to cut, grind, and drill other hard materials including stone, glass, ceramics, and metals. Diamond-tipped drill bits are standard in oil and gas exploration.
- Graphite electrodes — High-purity graphite electrodes are used in electric arc furnaces for steelmaking and in the production of aluminium, silicon, and other metals. Graphite is also used in pencil cores, high-temperature lubricants, and as a moderator in some nuclear reactors.
- Carbon fibre composites — Carbon fibre reinforced polymers (CFRP) offer a stiffness-to-weight ratio surpassing steel and aluminium. Used extensively in commercial aircraft fuselages (Boeing 787, Airbus A350), racing cars, wind turbine blades, sporting goods, and medical implants.
- Activated carbon — Activated carbon has an enormous internal surface area (up to 3,000 m²/g) created by steam activation of charcoal. It adsorbs organic molecules and heavy metal ions from water and air, making it essential in water purification, air filtration, gold recovery, and pharmaceutical manufacturing.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What are the main allotropes of carbon?
Carbon has several important allotropes. Diamond is the hardest known natural material, where each carbon atom is bonded to four others in a tetrahedral lattice, making it transparent and an electrical insulator. Graphite consists of stacked hexagonal layers where electrons can move freely, making it soft, slippery, and electrically conductive. Graphene is a single graphite layer, with extraordinary electrical and mechanical properties. Fullerenes (C60 and related structures) are spherical or tubular carbon cages with unique chemical reactivity.
Why is carbon the basis of life?
Carbon can form four covalent bonds simultaneously and can bond to itself to build chains, rings, and complex three-dimensional structures of arbitrary length. This gives it the ability to form the enormous molecules — proteins, DNA, lipids, carbohydrates — that make up living organisms. No other element combines carbon's bonding versatility with its stability under biological conditions.
What is carbon-14 dating?
Carbon-14 (¹⁴C) is a radioactive isotope produced in the upper atmosphere by cosmic rays. It decays with a half-life of 5,730 years. Living organisms continuously incorporate carbon-14 through photosynthesis and the food chain; when they die, the ¹⁴C stops being replenished and begins to decay. By measuring the ratio of ¹⁴C to stable ²¹C remaining in an organic sample, archaeologists and geologists can date material up to about 50,000 years old.
What is a carbon footprint?
A carbon footprint is the total greenhouse gas emissions caused by an individual, organisation, event, or product, expressed as an equivalent amount of carbon dioxide (CO2). Burning fossil fuels releases carbon stored over millions of years as CO2, contributing to atmospheric warming. Reducing carbon footprints involves using less energy, switching to renewables, and changing consumption patterns.
How is carbon fibre made and what is it used for?
Carbon fibre is made by oxidising and then carbonising a precursor organic fibre (usually polyacrylonitrile, PAN) at high temperature in an inert atmosphere. The process aligns carbon atoms into tightly bonded graphitic planes along the fibre axis. The resulting filaments are stiffer than steel at a fraction of the weight and are used in aircraft, racing cars, sports equipment, wind turbine blades, and prosthetics.