Essay on John Dalton

Submitted By tmivh
Words: 720
Pages: 3

John Dalton John Dalton was an English chemist, meteorologist, and physicist. He was born in September 6, 1766 and died in July 27, 1844. He is best known for his atomic theory, color-blindness studies and weather studies. Dalton’s atomic theory states five main points. It states that all matter is made of atoms. The second point is that atoms of the same element have the same mass and properties. The third point is that atoms cannot be created or destroyed. It also states that compounds are formed by a combination of two or more different kinds of atoms. The fifth point is that a chemical reaction is a rearrangement of atoms. Dalton’s theory is still valid in modern chemistry. Today we know that there are different kinds of atoms differing by their masses within an element known as isotopes. Isotopes of an element have the same chemical properties. Dalton’s theory became the theoretical foundation in chemistry. Joseph John Thomson Joseph John Thompson was born in December 18, 1856 and died in August 30, 1940. He was an English physicist. In 1897 Thompson discovered the electron in some experiments that he was doing to study the nature of electric discharge. He demonstrated that cathode rays were speedily moving particles. He measured their speed and specific charge, and concluded that these electrons were about 2000 smaller in mass. After his discovery, he was labeled as the most influential breakthrough in the history of physics after Sir Isaac Newton. Thomson also made a research on the nature of positive rays inn 1911. This helped in the discovery of isotopes. Thomson proved that isotopes could be broke by deflecting positive rays in electric and magnetic fields. This was later named mass spectrometry. In 1906 Thomson won a Nobel Prize for physics. He is considered as one of the greatest scientist in physics. Ernest Rutherford Ernest Rutherford was born on August 30, 1871, in Nelson, New Zealand and died in October 19, 1937 in Cambridge, United Kingdom. He was a physicist. Rutherford worked on radioactivity, coining the terms alpha and beta to describe the two different types of radiation emitted by uranium and thorium. He also observed that radioactive material took the same amount of time for half of it to decay, known as its “half life”. In 1907, Rutherford, Hans Geiger and Ernest Marsden carried out the Geiger-Marsden experiment, an attempt to examine the structure of the atom. The results of this experiment demonstrated the existence of the atomic nucleus, and it became an integral part of the Rutherford model of the atom. The Rutherford model of the atom was simplified in a symbol showing electrons circling around the nucleus. This symbol became popular, and it has been used by various organizations around the world as a symbol for atoms and atomic energy in general. In 1908, Rutherford was awarded the Nobel Prize in