A unit of pressure equal to the average atmospheric pressure at sea level (1 atm = 101.325 kPa).

The layer of gases surrounding Earth; also a unit of pressure.

The basic unit of a chemical element, consisting of a nucleus and electrons.

The total mass of an atom, typically expressed in atomic mass units (amu), roughly equivalent to the number of protons…

A unit of mass used to express atomic and molecular weights, defined as one-twelfth the mass of a carbon-12 atom.

The central core of an atom, composed of protons and neutrons and containing most of the atom’s mass.

The number of protons in the nucleus of an atom, which determines the element’s identity.

Adenosine triphosphate, a high-energy molecule that stores and supplies energy for many biochemical processes.

An enzyme that catalyzes the hydrolysis of ATP into ADP and inorganic phosphate, releasing energy.

An enzyme complex that synthesizes ATP from ADP and inorganic phosphate during cellular respiration and photosynthesis.