the formula for most elements is just a chemical symbol like He

a compound contains 2 or more elements that are chemicly bonded for example NaCl

a word equasion represents a chemical reaction using the name of substances envolved

an ion is a charged paricle formed when an atom looses or gains electrons eg Na1+

a pure substanc is is a material with only on element or compound

a mixture is 2 or more substances not chemicly bonded together

mixtures can be seperated be phisical prosesses. these prosesses do not envolve any chemicl ereactions and do not make any new substances

filtration is used to seperate an insoluble solid from a liquid

crystalisation is used to form crystals out of a liquid using evaporation

fractional distilation is used to seperate two liquids with different boiling temperatures

paper chromatography is used to seper ate mixtures of soluble solutions

john dalton discovered atoms in 1803, he belived that everything was made out of small spheres which could not be divided

jj thomson did experiments and discovered the electron. he then mad ethe plumb pudding model which was a big positive ball of charge with electrons embeded in it

in 1909 rutherford designed a experiment to test the plumb pudding model, it was a sheet of gold foil which he woulld shoot alpha particlas at. he saw that most of the particals went straight through bust some shot off in random directions, he then made a new model called the neuclear model