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300
About 450 B.C
A greek scholar named Empedocles said that all matter was composed of four "elements" water, fire ,air and earth. -
Period: 300 to Mar 14, 1200
developing models of matter
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400
about 400 B.C
another greek, democritus said that all matter was made of tiny particles that cant be broken down anymore and he named them atoms after the greek word atomos which means indivisible. -
500
About 350 B.C
The philosopher Aristotle liked and believed in Empedocles "four elements" and agreed that all matter was made of air, water, fire or earth. -
Mar 14, 600
A.D 500-1600
Do metals grow like plants ,ripening into gold? Many alchemists believed they did. Alchemists did experiments attempting to make gold from iron and lead. Although they made many of the tools we use now like beakers filters and stirring rodes and discovered many new substances they could not make gold out of lead and iron. -
Mar 14, 700
1650
A english scientist named robert boyle did not believe in the four element model. He came up with a new definition for the word element and this is what it was A pure substance that cannot be broken down into a simpler substance -
Mar 14, 1000
1800s
Daltons atomic model cannot explain why on a dry winter day you get a shock when you touch a metal doorknob. Thats because in the theory they didnt think of positive or negative charges. A new model was created, introducing tiny negatively charged paricles that could be seperated from their atoms and moved to other atoms.
In 1831 Michel Faraday found that electric currents could cause chemic changes in some compounds in solution.The atoms could gain eletric charge and form atoms called ions. -
Mar 14, 1100
1904
J.J thomson revised the atomic model futher, by explaining his discovery of very light negative particles called electrons. he also didexperiments with beams of much heavier positive particles. the new model became known as the "raisin-bun" model
-Atoms contain particles called electrons
-electrons have a small mass and a negitive charge
-the rest of the atom is a sphere of positive charge
-the eletrons are embedded in this ssphere, so that the resulting atoms are neutral or unchanged. -
Mar 14, 1200
1911
Ernest Rutherford,working at McGill University in Montreal made up an experiment to test thomson's and Nagaoka's models .He amied a type of radisation called alpha particles at a thin sheet of gold foil. he predicted that the the particles would pass throught the gold foilas indeed most of them did.however a small number of them didn'tthey bounced almost strait back from the gold foil.Rutherford was amazed and had to come up with a new model called "The nuclear model" -
late 1700s
Joseph Priestley was the first person to isolate oxygen scientifically, although he didnt know that oxygen was an element.Antonine lavoisier experimented with priestley's oxygen.
Meanwhile Henry cavendish exerimented by mixing a metal with acid which makes a flammable gas that was lighter then air. he didnt know he had made what we now call hydrogen, but he discovered that when his gas would burn in some of priestly's oxygen producing water.Until then scholars thought
water was an element. -
1808
By now it was accepted that matter was made of elements:the two models had come together. english chemist JohnDalton published a theory about why elements differ for one and other and form non elements. atomic model for matter stated that
- All matter is made of atoms which are too small to see.
-Each element has its own kind of atom with its own mass.
- compounds are created when different elements link to form molecules.
-Atoms cannot be created destroyed or subdivided in a chemical change
