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200
Discovery of particles 400 B.C
Another Greek named Democritus proposed the matter was made of tiny particles that could not be broken down further. He named them atoms after the greek word atomos meaning indivisible. -
300
Return of Empedocles theory
A philosopher named Aristotle believed that Empedocles theory was correct. He influenced a great number of people and Empedocles theory was used for nearly 2000 years. -
Period: 500 to
Trying to make gold.
Many alchemists thought they could create gold from iron and lead. They thought it could grow and ripen into gold. They created many useful tools but they never turned up succssessful. -
Going against Empedocles
An english scientist named Robert Boyle did not believe that Empodocles was correct. He thought that the definition of an element was "A pure substance that cannot be chemically broken down into simpler substances. He also suggested that air was not an element but a mixture. -
isolating oxygen and producing hydrogen
A scientist named Joseph priestly successfully isolated oxygen. He was not aware that oxygen was an element. Another man named Antoine Lavoiser suggested that air is a mixture of at least 2 gasses, one of them being oxygen. -
Creating Hydrogen
A man named Henry Cavendish created Hydrogen by mixing metal and acid. Before this experiment scholars thought water was an element. -
Matter made up of elements
A chemist named John dalton published the theory of why elements differ from each other and from non-elements. He had a model that suggested the following
- that all matter is made of atoms, which are particles too small to see.
-each element has its own kind of atom, with its on particular mass.
-compounds are created when atoms of different elements link to form molecules.
-atoms cannot be created, destroyed, or subdivided in chemicle change. -
Electric atoms
in the early 1830's a man naed michael faraday created a different version of daltons model. This one stated 3 statements.
-matter must contain positive and negative charges.
-opposite charges attract and like charges repel.
-atoms combine to form molecules because of electrical attractions between atoms. -
changing daltons theory-1800's
Daltons theory did not include the fact that matter can develope positive and negative charges. So a new model was built that introduced tiny negatively charged particles that could be separated from their atoms and moved to other atoms. -
Meanwhile in Japan...
While J.J. Thomson was creating his own model a Japanese scientist named H. Nagaoka created a large sphere to model an atom as a large positive sphere with a ring of negative electrons surrounding it. -
introduction of protons
a man named J.J. Thomson experimented with beams of heavy positive particles now known as protons. He also tweeked the model a little bit.
-atoms contain particles called electrons.
-electrons have a small mass and a negative charge.
-the rest of the atom is a sphere of positive charge.
-the electrons are embedded in this sphere so that the resulting atoms are neutral or uncharged. -
Rutherfords Model
-An atom has a tiny, dense, positive core called the nucleus.
(The nucleus deflected the particles)
-The nucleus is surrounded mostly by empty space, containing rapidly moving negative electrons.
(The alpha particles passed through this with no problems. -
Testing and creating models
A man named Ernest Rutherford decided to test J.J. Thomson and H. Nagaoka's models. He shot alpha particles a a sheet of gold foil expecting the alpha particles to go through. There was a different outcome. Most of the alpha particles had passed throught the gold foil. But there was a few that bounced back off the gold foil. -
Discovery of Elements 450 B.C
A greeek scholar named Empedocles suggested that matter was composed of four "elements": Earth, Air, Fire, and water. He proved that, even though air is invisible, it is still matter because it takes up space.
