Carbon-12 is the most abundant stable carbon isotope, comprising 98.93% of Earth's carbon. Contains 6 protons, 6 neutrons, and 6 electrons. Created through triple-alpha process in stars
Chemical symbols are abbreviations used for elements, groups, and compounds. Element symbols typically consist of one or two Latin letters. Some symbols come from classical Latin and Greek vocabulary. Temporary symbols may be assigned to newly synthesized elements
Mass number (A) equals total protons and neutrons in an atomic nucleus. Mass number is written after element name or as superscript. Each isotope has different mass number, difference equals neutrons
Oxygen was discovered by Scheele in 1772 and Priestley in 1774. Earth's crust contains 46% oxygen, atmosphere 21%, seawater 89%. Oxygen forms compounds with practically any element
Tables based on 2021 table with changes from 2019 for Ar, Hf, Ir, Pb, and Yb. Values revised for Gd, Lu, and Zr in 2024. Atomic weights available in five significant figures
Atomic mass is the sum of protons, neutrons, and electrons in an atom. Electrons are negligible and not included in calculations. Atomic mass can be expressed in amu (1/12th of carbon-12) or Dalton's