-
400 BCE
Democritus
His theory purely by philosophical means. Just by using analogies of his sense experiences he gave a picture of atoms and distinguished them by shape, size, and the arrangement of their parts. Democritus was able to understand that there is no limit to how small or big something can be which gave him the idea that there were little particles that make up everything -
400 BCE
Democritus
2.Since Democritus really based his theory on observations and natural curiosity, "experiment" earns old air quotes here. Going forward you will need to match the scientist with his or her theory and understand the experiment that supported it. For Democritus we sometimes just tag his experiment as "Big Thoughts." -
400 BCE
Democritus
4.Democritus’s model stated that matter consists of invisible particles called atoms and a void (empty space). He stated that atoms are indestructible and unchangeable. Also that they are homogeneous, meaning they have no internal structure. His atomic model was solid, and stated all atoms differ in size, shape, mass, position and arrangement, with a void exists between them. -
400 BCE
Democritus
3.Democritus believed the atom was it - smallest particle of matter. Case closed. Makes sense if you stop and think about it. He was already talking about tiny invisible things, and there was no technology available to him that would allow him to see the unseeable. I think it's pretty remarkable he was able to develop a good basic concept of atoms to begin with. -
John Dalton
The experiment that they carried out to explore the atomic structure- Many consider 2008 the 200th anniversary of atomic theory, John Dalton’s momentous theory of the nature of matter. Dalton (1766–1844) proposed that all matter in the universe is made of indestructible, unchangeable atoms -
John Dalton
Throughout his life Dalton was interested in the Earth's atmosphere, and he recorded more than 200,000 atmospheric observations in his notebooks. These observations led Dalton to study gases, and from the results of his experiments he was able to formulate his atomic theory. -
John Dalton
All matter is made up of atoms.
All atoms can be identified by mass and properties
All compounds are made up of atom combinations
All chemical reactions are a rearrangement of atoms
If an element reacts, their atoms may sometimes combine into more than one simple whole-number ratio -
John Dalton
1) All matter is made of atoms. Atoms are indivisible and indestructible. 2) All atoms of a given element are identical in mass and properties 3) Compounds are formed by a combination of two or more different kinds of atoms. 4) A chemical reaction is a rearrangement of atoms. -
John Dalton
-
Sir J.J. Thomson
Thomson set out to prove that the cathode rays produced from the cathode were actually a stream of negatively charged particles called electrons -
Sir J.J. Thomson
Hertz had previously tried and failed to observe such a deflection, which gave support to the view that the cathode rays are not electric particles. Thomson realised that the reason for Hertz's failure was that the gas in his container was not at a sufficiently low pressure. Consequently, positive and negative ions in the gas neutralised the electric field that Hertz was applying. Thomson reduced the pressure and observed a deflection. -
Sir J.J. Thomson
The British physicist Joseph John (J. J.) Thomson (1856–1940) performed a series of experiments in 1897 designed to study the nature of electric discharge in a high-vacuum cathode-ray tube, an area being investigated by many scientists at the time. -
Sir J.J. Thomson
Thomson realised that the accepted model of an atom did not account for negatively or positively charged particles. Therefore, he proposed a model of the atom which he likened to plum pudding. The negative electrons represented the raisins in the pudding and the dough contained the positive charge. Thomson's model of the atom did explain some of the electrical properties of the atom due to the electrons, but failed to recognise the positive charges in the atom as particles. -
Sir J.J. Thomson
J.J. Thomson discovered electrons and noticed that an atom can be divided. Also, he concluded atoms are made of positive cores and negatively charged particles within it. He developed the Plum Pudding Model before the atomic nucleus was discovered. This model shows that the electrons are surrounded by a "pudding" of positive charges to balance the negative charges. Today, J.J. Thomson's discoveries have helped people to have a better understanding of the atom and its generic makeup.
