Mass: definition in chemistry
Mass: The amount of matter in an object. Unlike weight, it does not change with gravity.
Mass is measured in kilograms (kg) or grams (g) using a balance, while weight is the force of gravity on that mass and is measured in newtons. An astronaut has the same mass on the Moon as on Earth but weighs only about one-sixth as much there. In chemistry, mass is conserved: the total mass of the products of a reaction equals the total mass of the reactants.
Examples
- A liter of water has a mass of about 1 kilogram
- A paper clip has a mass of about 1 gram
- A carbon-12 atom has a mass of exactly 12 atomic mass units
- A proton has about 1,836 times the mass of an electron
On the periodic table
Each element's box shows its average atomic mass, which generally increases with atomic number across the table.