1 The Atomic Models From the Ancient Greeks to the actual models…all you need to know.

2 Historians have discovered this from the quotations of other Greeks (most of the original documents by Leucippus and Democritus have been lost). In the 4th century BC, the well known philosopher Aristotle vehemently argued that the atomic theory was completely incorrect and was therefore dismissed by scientists for many decades. In fact, the Catholic Church agreed with Aristotle's position and announced that atomistic ideas were equivalent to those of Godlessness. "Democritus of Abdera said that there is no end to the universe, since it was not created by any outside power." The concept of the smallest particle was conceived in the 5th century BC by Leucippus of Miletus. His pupil, Democritus of Abdera (picture) developed five major points that their theory was based upon. The Greek Beginning

3 1.All matter is made up of undividable particles called atoms. 2.There is a void, which is empty space between atoms. 3.Atoms are completely solid. 4. Atoms are homogeneous, with no internal structure. 5.Atoms vary in: a.Size b.Shape c.Weight The 5 points of their conclusion are as follows...

4 John Dalton’s Model In September of 1803, John Dalton wrote his first table of atomic weights in his daily logbook. In 1830, he stated his most well-known quote Two years after he developed his atomic weights, he published them in a book called "A New System of Chemical Philosophy. In it he was the first to propose that elements be identified with symbols. However, only 3 or 4 pages in the third chapter discussed the atomic theory he proposed. In this theory, there are four basic ideas... 1) chemical elements are made of atoms. 2) the atoms of an element are identical in their masses 3) atoms of different elements have different masses 4) atoms only combine in small, whole number ratios such as 1:1, 1:2, 2:3 and so on. 5) atoms can be neither created nor destroyed John Dalton is now called the father of modern atomic theory for his efforts. His atomic theories were introduced in 19th century England. Interesting Fact: The unit for atomic weight was called a "dalton" for many years. Today, it is used in biochemical circles, (e.g. "The atomic weight of that protein is 35,000 daltons.")

5 Joseph John Thompson On April 30, 1897, Joseph John Thomson announced that cathode rays were negatively charged particles which he called 'corpuscles.' He also announced that they had a mass about 1000 times smaller than a hydrogen atom, and he claimed that these corpuscles were the things from which atoms were built up. The Plum Pudding Model This hypothesis was not generally accepted until 1899 when an Irish physicist named George Francis FitzGerald proposed that the "corpuscles" Thomson spoke of were actually free electron particles. Thomson designed the famous "plum pudding model" shown below.

6 Ernest Rutherford New Zealander, studied under J. J. Thomson at the Cavendish Laboratory in England. He was the first scientist to propose the theory of the nuclear atom. His experiment, shown to the right, proves that "uranium emanations were shown to consist of three types of rays, alpha (helium nuclei) of low penetrating power, beta (electrons), and gamma, of exceedingly short wavelength and great energy." Basically, he proved that the atom had a nucleus.

7 Niels Bohr’s model Niels Bohr came up with the Bohr Model in It is referred to as the "planetary model". In the picture, the red and green balls symbolize the neutrons and protons that form the nucleus. The electrons orbit the nucleus like the planets orbit the Sun. Bohr’s model of the Carbon atom