Carbon (Z=6): The Element of Life

Carbon: The Element of Life and Materials

Carbon (symbol C, atomic number 6) is a chemical element essential to life on Earth. It forms the basis of organic chemistry and is found in a wide variety of structures and materials, from long chains of organic molecules to innovative materials like nanotubes and graphene.

Contribution of Carbon to Vital Processes

Carbon is a fundamental element of organic matter. It forms the backbone of essential biomolecules such as carbohydrates, lipids, proteins, and nucleic acids. In the form of CO₂, it is assimilated by primary producers through photosynthesis and redistributed through food webs. Consequence of a deficiency: Impaired synthesis of biomolecules, compromising growth, reproduction, and cellular regeneration.

History of Discovery

Antiquity: First Uses
Carbon was known in antiquity in the form of charcoal, soot, and diamonds. These different forms were used in various applications, but their chemical nature was not yet understood.

1804: Identification by Antoine Lavoisier
Lavoisier demonstrated that charcoal, when burned in oxygen, produces carbon dioxide (CO₂), allowing this element to be distinguished from other substances.

1826: First Synthesis of Organic Compounds
The first organic compounds were synthesized from carbon, marking the dawn of organic chemistry.

Atomic Structure

Constitution: Carbon has 6 protons, 6 neutrons, and 6 electrons in its ground state.
Isotopes:

• Carbon-12 (¹²C): stable isotope, 98.93% natural.
• Carbon-13 (¹³C): stable isotope, used in spectroscopy and dating.
• Carbon-14 (¹⁴C): radioactive, used in radiocarbon dating (T₁/₂ ≈ 5730 years).

Physical Properties

• Solid at room temperature, existing in various allotropic forms (graphite, diamond, fullerene, etc.).
• Melting point: varies depending on the allotropic form (diamond ≈ 3915 K, graphite ≈ 4000 K).
• Electrical conductivity: good in graphite, excellent in graphene and nanotubes.
• Density: variable, 2.267 g/cm³ (graphite), 3.515 g/cm³ (diamond).
• Hardest allotropic form: diamond.

Chemical Reactivity

• Highly reactive in the presence of dioxygen, forms carbon dioxide (CO₂) during combustion.
• Unique ability to form long chains of molecules with other carbon atoms, the basis of organic chemistry.
• Forms various compounds: alcohols, acids, hydrocarbons, polymers.
• Forms covalent bonds with various elements such as hydrogen, oxygen, and nitrogen.

Industrial and Technological Applications

• Materials: use of carbon in composite materials, particularly for aircraft, vehicles, and sports equipment.
• Nanotubes and graphene: these allotropic forms of carbon have revolutionized the fields of electronics and nanotechnology.
• Chemical industry: production of plastics, rubber, oils, and fuels.
• Filtration and purification: use of activated charcoal in water and air treatment.

Biological and Ecological Role

• Carbon is the basis of organic chemistry and all molecules essential to life, such as amino acids and nucleic acids (DNA, RNA).
• Central role in the carbon cycle, a vital biogeochemical loop for regulating Earth's climate.
• Presence in marine sediments, soils, and the atmosphere as carbon dioxide (CO₂), involved in the processes of photosynthesis and respiration.

Cosmological and Astrophysical Role

• Carbon is an essential element in the formation of stars and planetary systems.
• Presence in nebulae, forming complex molecules that can be precursors to life.
• Role in the formation of interstellar dust grains and in the chemical evolution of galaxies.

Fundamental Physical Issues

• Carbon has allowed the study of the properties of covalent bonds and molecular orbital theory.
• Carbon structures, such as diamond and graphite, are examples of crystalline systems used to understand the theory of materials.
• Graphene, a single layer of carbon atoms, has opened new perspectives in quantum physics and conductivity.