-
450 BCE
first 4 elements
A greek scholar named Empedocles proposed that there are 4 elements, water, air, earth, and fire. He also did experiments to prove that even though air is invisible, it still takes up space, and is a form of matter -
400 BCE
First particles
A greek Democritus had an idea that matter was made out of tiny particles that can not be broken down any further. He named them after the greek word "invisible". witch meant different elements were made out of different kinds of atoms. although people did not really accept these ideas. -
350 BCE
Acceptance of the four elements
A popular philosopher named Aristotle believed in the four element theory, even after the new "discovery" of atoms, his influence was so big, and his writings were read by so many people, the four element theory was accepted for almost 2000 years. -
500
Trying to grow gold
from 500 A.D - 1600's Many alchemists believed that they could turn cheap metals into gold. for centuries they kept doing more and more experiments to try and successfully "grow" the gold. They never managed to turn these metals into gold, however they did create many of the laboratory tools that we still use to this day, like stirring rods and beakers. They even created chemical symbols for substances, that we now see as elements and compounds. -
New definition
In 1650 an English scientist by the name of Robert Boyle, didn't believe in the theory that there are only four elements. He created a new definition for the word element "simple unmitigated bodies" and this quickly became the new modern definition of an element. Robert Boyle also believed that air was in fact not an element, but a mixture -
Isolating oxygen
In the late 1700s Joseph Priestley was the first person to successfully isolate oxygen. At the time he didn't know that oxygen was an element, until Antoine Lavoisier started to experiment with Josephs oxygen until he concluded that oxygen was in fact a mixture of at least 2 or more gases. At the same time Henry Cavendish was experimenting with mixing metals with acids. He ended up with a flammable gas that turned out to be hydrogen, and that it could burn the isolated oxygen and create water. -
why each element is diferent
at this time it was widely accepted that all matter is made by elements. English chemist John Dalton published a theory about why each element is different from another, he said "All mater is made from particles witch are too small to see, each element has its own kind of atom with its own particular mass, compounds are created when atoms of different elements link to form molecules, and atoms can not be created, destroyed or subdivided in chemical changes" -
electrical currents in atoms
in 1831 Micheal Faraday found out that an electric current could cause chemical changes in some compounds. He found out that atoms could take electric charges and create charged atoms that are called "ions". He then created a different version of Dalton's model: 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 -
Electrons and Protons
J. J Thomson further added/changed Dalton's atomic model, to explain his discovery of electrons, and his experiments with protons: 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, electrons are embedded in this sphere so that resulting atoms are neutral or uncharged. This helped a Japanese scientist named H. Nagaoka, who later modeled the atom as a large sphere surrounded by negative electrons -
The nuclear model pt.2
Rutherford was amazed at what happened and came up with another new model "the nuclear model": An atom has a tiny, dense, positive core called a nucleus, the nucleus (surrounded by mostly empty space) contained rapidly moving negative electrons, witch explains why a few times the radiation bounced off of when he did his experiment. -
The nuclear model pt.1
Ernest Rutherford, while working at McGill university designed an experiment to test both Thompson's and Nagaoka's model's. He aimed a radiation of alpha particles at a thin sheet of gold foil, he predicted that based on Thomson's raisin-bun model that the particles should pass directly through the piece of foil, and most of them did, except for a very small amount of particles that got reflected back from the foil
