What is Law of definite composition?
The '''law of definite proportions''' states that a [[chemical compound]] always has exactly the same [[Proportions|proportion]] of [[Chemical element|elements]] by [[mass]]. Joseph Proust, a French chemist, first observed it in 1797. For this reason, it is sometimes called '''Proust's law.''' ==Overview== Amounting to the same thing is the '''law of constant composition'''. This states that all samples of a given chemical compound have the same elemental composition by mass. For example, [[oxygen]] makes up about <sup>8</sup>/<sub>9</sub> of the mass of any sample of pure [[water]], while [[hydrogen]] makes up the remaining <sup>1</sup>/<sub>9</sub> of the mass. The law of definite proportions is the basis of [[stoichiometry]], together with the [[law of multiple proportions]]. Meanwhile, it is notable that there are some compounds, where this law cannot be applied. They are sometimes called non-stoichiometric compounds, which are commonly [[Metal|metals]]. ==Related pages== * [[Valency]] * [[Stoichiometry]] * [[Atomic orbital]] * [[Atomic physics]] * [[Molecular orbital]] * [[Chemical formula]] * [[Quantum mechanics]] * [[Amount of substance]] * [[Albert Einstein#Mass-energy equivalence|Mass-energy equivalence]] {{chemistry-stub}} [[Category:Physics]] [[Category:Science]] [[Category:Chemistry]]