Carbon12
Carbon-12 (12C) is the most abundant isotope of carbon, accounting for 98.93% of all carbon found on Earth. It is the basis for the atomic mass unit (amu), defined as exactly one-twelfth of the mass of a neutral, unbound atom of carbon-12 in its nuclear and electronic ground state. This definition provides a precise and internationally agreed-upon standard for measuring the masses of atoms and molecules.
Carbon-12 has a nucleus consisting of 6 protons and 6 neutrons. It is a stable isotope, meaning it does not undergo radioactive decay. This stability, combined with its abundance, makes it crucial in various fields including chemistry, physics, and biology.
In chemistry, carbon-12 is the foundation for defining the structure and properties of organic compounds. The vast diversity of organic molecules, essential to life, relies heavily on the unique bonding capabilities of carbon atoms.
In physics, carbon-12 serves as a calibration standard in mass spectrometry, a technique used to determine the mass-to-charge ratio of ions. Its precise mass allows for accurate measurement of other atomic and molecular masses.
In biology, carbon-12 is a fundamental component of all living organisms. It is incorporated into essential biomolecules like carbohydrates, lipids, proteins, and nucleic acids. The carbon cycle, a series of processes by which carbon atoms circulate between the Earth's atmosphere, oceans, land, and living organisms, predominantly involves carbon-12.
The stability and abundance of carbon-12 also make it a useful tracer in some scientific studies, although less commonly than its radioactive isotope, carbon-14.