350 B.C.Empedocles' "four element" model was accepted and believed by the philosopher Aristotle. The "fou element" model was later accepted for almost 2000 years, because of Aristotle's Great influence and writings.
400 B.C.A greek man, named Democritus, had suggested that matter was made of tiny particles, called atoms. The atoms couldn't be broken down further than they already were.
450 B.C.Empedocles, a greek scholar. Proposed that all matter was composed of four "elements": water, fire, air, and earth. He also suggested that mixing these elements in different proportions created new substances.
A.D. 500-1600Many alchemists belived that metals grew like plants and ripened into gold. For centuries alchemists performed many experiments trying to create gold from metals like lead and iron. No one ever turned lead into gold.
The alchemists created tools that we still use in labratorys, and after creating many new substances they still accepted Empedocles' "Four Element" model.
1650Robert boyle, an english scientist. Didnt believe in Empedocles' "Four element" model. Boyles' definition four the word element, later became the modern definition of an element: a pure substance that can't be chemically broken down into simpler substances. Air was not an element, but a mixture to Robert Boyle.
Late 1700sJoseph Priestley, first person to isolate oxygen scientifically, not knowing that oxygen was an element. Antoine Lavoisier soon recognized this fact. When experimenting with Priestly's oxygen, Lavoisier concluded that air must be a mixture of at least two gases, one being oxygen. Henry Cavendish experimented mixing a metal with acid, making a flammable gas, lighter than air (hydrogen). he discoverd that it would burn in Priestley's oxygen(water).Until then scholars believed water was an element.
1808By this time it was accepted that matter was made of elements. John Dalton an English chemist had published a theory stating why elements are different from each other & non elements.
Dalton’s atomic model for matter stated that:
- All matter is made or atoms.
-Each element has its own kind of atom, w/ its own mass.
-Compounds are made when atoms of different elements link forming molecules.
-Atoms can't be created, destroyed or subdivided in chemical changes.
1800sIn 1831 Michael Faraday Found that eletric currents could cause chemis changes in certain compounds in solution. The atoms could gain electric charges, forming charged atoms, called ions.
In this modified version of Dolton's model:
- Matter must contain + and - charges.
- Opposite charges attract and like charges repel.
- Atoms combine to form molecules because of electrical attractions between atoms.
1904J.J. Thomson revised the atomic model further, to explain his discovery of electrons. Thomson did experiments with beams of heavier + particles (Protons). The model had been called the " Rasisin Bun" model.
- 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.
1911Ernest Rutherford, Designed a expirement to test Thomson's and Nagaka's models.
After Rutherford had done his tests he had to come up with a new model - The Nuclear Model:
- An atom has a tiny, dense, positive core called the nucleus.
- The nucleus is surrounded mostly by empty space, containing rapidly moving negative electrons.