atoms of each element are represented with symbols (eg. Na is sodium)

Compounds contain two or more different elements chemically combined

They can be represented with formulae of the elements they were formed with

Chemical reactions always involve to formation of one or more new substances (and often a detectable energy change)

Compounds are formed from from elements in chemical reactions

formulae is calculated by using the charge of the ion of the element - (needs overall zero charge)

the chemical properties of each substance in the mixture are unchanged

contains two or more elements or compounds not chemically bonded

eg. separating sand from water or excess reactant from a solution

the process of forming crystals from a solution by allowing the solvent to evaporate

heat up a solution, substance with lower bpt will evaporate go through condensing tube & into a different vessel

the process of separating crude oil into hydrocarbons with similar numbers of carbon atoms

separation of a mixture into its components, the mixture is dissolved in a fluid

J.J Thompson (1897): discovered electrons // plum pudding model // electrons stuck to outside of a solid sphere // used particle accelerate

Ernest Rutherford (1911): GOLD FOIL EXPERIMENT: projected a beam of particles at a thin sheet of gold to probe inner structure of the atom // some rebounded & came back // most of an atom is empty space w/ dense positive core

John Dalton (1802): atoms are small & indivisible // all elements were made with different atoms

Niels Bohr (1913): proposed the atom was like a tiny solar system // electrons orbit the positive nucleus

Democritus (400BC): "If I cut an item in half is there a point where you can't cut it in half anymore // atoms are the smallest particles

James Chadwick (1932): concluded there was the existance of zero charge neutrons // atomic mass of elements was often double it should be

atoms of different elements have different numbers of protons

In an atom, the no. electrons is the same as the no. protons in the nucleus

Atoms of the same element can have a different no. neutrons (isotopes)