In a chemical reaction, matter cannot be created or destroyed. mass of products = mass of reactants
The Law of definite proportions or constant composition (Joseph Proust)
All samples of a given pure compound, regardless of their source or how they were made always contain same elements in the same parts (fraction) of mass.
The Law of Law of multiple proportions (John Dalton)
when two elements A and B, react to form more than one compound, the different masses of B that combine with a fixed mass (1g) of A can be expressed as a ratio of small whole numbers.
-smallest particle of an element. -splits into subatomic particles. such as: electrons (-ve), protons (+ve) and neutrons (neutral) -concept of splitting atom started with discovery of: cathode rays, x-rays, the electrons.
The electron (J.J Thompson)
Discovered the electron while working on his cathode ray experiment. proposed that cathode rays consist of tiny negatively charged particles, which we now call electrons. measured the charge: mass ratio of the electron. mass/charge = -1.76x108 coulombs.
The electron (Robert Millikan)
used the oil drop experiment to calculate the charge on a single electron.\ charge on any drop was always a whole number multiple of -1.6022x10-19 coulombs. further calculated the mass of an electron to be 9.10x10-28 g.