-
370
Democritus
Born in about 460 BC. Died in 370 BC. He proposed that everything is made up of atoms, and these are the smallest parts of matter. Between atoms is empty space. Atoms are always moving. There are an unlimited number of atoms. And atoms differ in shape and size. He proposed that the solidness of material is due to the shape of the atoms. -
Robert Boyle
Born on 25th January 1627. Died on 31st December 1691. He was one of the early chemists to propose that atoms exist. He conducted experiments attempting to turn metal into gold. He knew that elements were made up of small particles of a particular size. He was able to give the differences between mixtures (substances that can be seperated by filtration, evaporation, etc.) and compounds, which cannot be seperated. He proposed the idea that atoms exist. -
John Dalton.
John Dalton was born in 1766, in Cumberland, England. He died in 1844. John Dalton was influenced by Elihu Robinson who was a wealthy instrument maker, and John Gough, a blind polymath. Gough taught Dalton Latin, Greek, French, math, and science. In return Dalton had to read to him from books and newspapers. Gough also encouraged Dalton to keep a meteorological journal. Dalton found that all matter is composed of very small, invisible, and indestructible particles which were atoms. -
John Dalton continued...
That atoms of an element are all the same in every way including weight but differ from the atoms of every other element. When elements combine to form compounds their atoms combine in numerical proportions, like one to one, two to one, four to three. Dalton worked out the weights of the different atoms from the proportions by weight of the elements in some compounds. He was the first to prepare a table of atomic weights. -
James Maxwell
Born on 13th June, 1831. Died on 5th November, 1879. Electric and magnetic fields travel in waves and at speed of light. He produced a model of electro magnetism and electro magnetic fields. He developed theories leading to discovery of the existence of electro magnetic radiation. Energy exists in fields and bodies. His theories are now used as radio, television, radar, microwaves and thermal imaging. -
Sir William Crookes
Born in 1832. Died in 1919. William Crookes discovered that selenium and thallium. He also developed experiments in analytical chemistry. He developed Crookes tubes, which investigate cathode rays and wrote many research papers on spectroscopy (the colours released by elements). He also showed that light travels in straight lines. -
Joseph John Thomson
J.J. Thomson was born in Cheetham Hill on December 18, 1856. He died on August 30, 1940. What Thomson did was study the positive charged ions (positive rays). This lead to his famous discovery, he had channelled a stream of ionized neon through a magnetic field and used some deflection techniques to measure the charge to mass ratio. In doing this he discovered that neon was made up of two different kinds of atoms. -
Joseph John Thomson continued...
Thomson also determined that all matter is made up of tiny particles that are much smaller than atoms. Originally he had called these tiny particles ‘corpuscles’ but then they later changed to be called electrons. -
Max Planck
Born in Kiel, Germany, on April 23, 1858. Died at Gottingen on October 4th, 1947. Energy can be given off or absorbed in particular amounts. Known as quantum. Energy is carried in tiny units, known as quanta. -
Louis De Broglie
Born in Dieppe on 15th August, 1862. Died on March 19th, 1987. Light contains particles which are energy and these form light waves. All particles are moved by waves. Particles can behave like waves. Waves can behave like particles. He was able to explain behaviour of atoms, molecules, and protons. -
Ernest Rutherford
Born on August 30th, 1871 In Nelson, New Zealand. Died on October 19, 1937 in Cambridge. His most important discovery was the structure of the atom. He showed that the centre of the atom is positively charged. It also has the most mass of the atom. Rutherford discovered that the half-life or radioactive elements and applied this to his studies of age determination of rocks by measuring the decay period of radium to lead-206. -
Albert Einstein
Born at Ulm, in Württemberg, On March 14th, 1879. Died on 18th April 1955. He proposed the nature of light. He proposed the law of thermo dynamics and existence of atoms which he proved through testing. Matter and energy are exchangeable. His theories form the basis of our understanding of atomic energy. Proposed the famous equation e=mc2 which talks about movement of molecules. Also proposed the photon theory of light. -
Niels Bohr continued...
All the properties of an atom are determined by the electrons in the outer orbitals. He discovered that electrons are moving around the outside of an atom. He also discovered that they move in energy levels called shells. He found that electrons can gain energy and move to a higher energy level. -
Niels Bohr
Born in Copenhagen on October 7th, 1885. Died in Copenhagen on November 18th, 1962. He found that electrons move in orbitals (groups of two electrons). He explained that the negative electrons are attracted to the positive nucleus and this is what keeps the atom held together. When electrons gain energy, and jump to a higher energy level, they give off light when they move back down to their original energy level. -
Gustav Hertz
Born July 22, 1887. Died October 30, 1975. He showed that each atom must absorb a particular amount of energy for an electron to move to a high energy level. He designed a way of separating neon isotopes (atoms which have the same number of protons but a different number of neutrons). -
Erwin Schrodinger
Born on August 12th, 1887, In Vienna. Died on the 4th of January, 1961. He found that the speed and position of electrons can be determined. He proposed that the electron cloud model of the atom. His model also describes electrons moving in orbitals and gives a probability of where electrons are at a particular point of time. -
Henry Moseley
Born in 1887. Died in 1915. Was able to extend Mendeleev’s periodic table by showing that the order of the elements in the periodic table also coincided with spectral lines of the elements. Spectral lines are lines of colour, which are unique to each atom and are determined by the electron numbers and energy levels. The modern periodic table is based on Moseley’s work showing the atomic number, the number of protons in an atom. -
Enrico Fermi
Born in Rome on 29th September, 1901. Died in Chicago on 28th November, 1954. The nucleus of the atom is able to undergo transformation and that the number of neutrons in an atom can change. He discovered the nuclear fission where the atom breaks down releasing energy. His work led to the ability to make atoms outside of the periodic table. Used neutrons as projectiles, shooting them into an atoms nucleus. This created isotopes.
