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Democritus
• Democritus was a philosopher who lived from 460 BC to 370 BC in Greece • Everything is made up of atoms that are not invisible and are indestructible. Atoms are always in motion. • Our senses distinguished them and their shape and size. • He was influenced by Leucippus who was thought to be the first atomic theory -
Isaac Newton
• Newton recognised that there are forces between atoms and that the chemical properties of matter are affected by forces and atoms. Atoms affect the chemical properties of matter and that atoms make everything work.• He lived from 1642 – 1727 -
Antoine Lavoisier
• Was able to make accurate measurments of cemical compunds in the 1780s, about 30 years before daltons theory. It was found that compounds containing more then one element always has about the same amounts of each element. • He proed the law of conservation of mass which is:• Mass cannot be created or destroyed, the mass of reactants must equal the mass of the products.• When oxygen and hydrogen combine water is formed.• After he tried to take credit for the pristleys experiment of mass he -
John Dalton
• John Dalton made a point that matter could not be broken down to anything smaller then the atom which are tiny particles in early 19th century • He said that atoms were tiny, indivisible, indestructible particles and each one has their own mass, size and chemical behaviour that was determined by the kind of element. • Every element was different • We still use this theory • He looked at the ancient Greek philosophers about their atom work then discovered more and the weight of chemical mea -
Dmitri Mendeleev
• He lived from 1834 – 1907• Dmitri used a table to revolutionize and give us the understanding of properties of atoms that is still used today.• In the late 1860s he began working on the periodic table of elements. He arranged the 63 elements into groups by their atomic weights and their similar properties. There were 3 gaps in his table he predicted that a new element would be found one day and he was right those elements were found during his life and they were gallium, scandium and germani -
George Johnstone Stoney
• He lived from 1826 – 1911• His most important work was about the conception and calculations of the magnitude of the atom and the particle of electricity which me made the term “electron” . He also estimated the number of molecules in a cubic millimetre of gas, he got this by using the kinetic theory of gas at room temperature and pressure. • He was known for his contribution to developing the theory of electrons by H.A Lorentz in 1902 from his Nobel lecture • Stoney suggested that there ar -
Joseph John Thomson
• Thomson discovered that atoms were dividible and were made up of even smaller particles. His experements showed that inside the atom there were very small negatively charged particles “electrons”. He also showed that there are positively charged material inside the atom, although this material was unclear. Thomson suggested that the atom is like a plum pudding, in which the positively charged material is the ‘cake’ and electrons are the fruit, this was called Tomson plum pudding model atoms -
Max Planck
• Planck discovered the quantum theory, by the study of light and radiation. He hypothesised that matter was discrete rather than continuous. This means that atoms behave differently to the human-scale world. • His theory was that by the vibrating of particles of light could only emit certain forms of energies. This contributed to understanding that energy determined in colour or frequency instead of intensity. • Lived from 1858 - 1947 -
Hantaro Nagaoka
• Nagako developed an incorrect ‘planetary model’ of the atom which was based on Saturn’s rings. It had a massive nucleus with electrons revolving around the nucleus, bound by electrostatic forces. Although this was wrong, even though the electrons revolving around the nucleus was correct and was abandoned in 1908. The model although incorrect helped to develop the idea of the nucleus being orbited by electrons. • He lived from 1865 - 1950 -
Albert Einstein
• Even though there was no actual evidence of the existence of atoms, until Einstein published three scientific papers in 1905.The three papers included Einstein’s theory of relativity which included the formula E=mc2 meaning energy equals mass times the velocity of light squared.He also made the Brownian theory that was the atomic theory of matter. The theory consists of the irregular movement of minute particles within liquid or gas, this all was an extension of the effects seen by Robert B -
Robert Millikan
• Millikan measured the charge of an electron by his oil-drop apparatus. He also proved that all electrons in every atom have the same charge. • He lived from 1868 - 1953 -
Ernest Rutherford
• Rutherford created a model of the atom that included: very small positively charged nucleus that was orbited by electrons. He also hypothesized on the existence of ‘neutrons’ which could somehow compensate for the repelling effect of the protons by causing an attractive nuclear force, which keeps the nucleus from breaking apart. He also discovered the basic form of an atom regarding protons and electrons.• He lived from 1871 – 1937 -
Henry G.J. Moseley
• Moseley determined the charge of most nucei using X-rays. He also discovered that the atomic number and number of protons in an element were equal, leading to the periodic table of elements that are arraged by atomic number instead of atomic mass, which helped organise it better. This meant that all atoms of different elements have different weights.• Atoms were arranged according to increasing atomic number. The modern periodic table is based on the atomic numbers of the elements. -
Niels Bohr
• Bohr suggested that when atoms are heated or excited the electrons can jump to higher levels and when cooled they drop to lower levels. Electrons energy levels can be imagined as concentric circles around the nucleus. He predicted that the levels had a maximum capacity of electrons with the innermost being 2. • His main points where that: electrons orbit the nucleus in set sizes and energy, The size relates to amount of energy so lowest energy is in smallest orbit. -
James Chadwick
Chadwick explored further into what the unidentified mass was made of, he kept of trying over and over again to find the neutron and never gave up because he was so sure it was there. He discovered a 3rd type of subatomic particle and named it the ‘neutron’. Neutrons stabilize the protons in the nucleus, this would prevent the protons from repelling each other. Both about the same size and found in the nucleus, however neutrons have no electrical charge. Helping to know why atoms stay together
