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John Dalton
After expirimenting with gasses, Dalton developed the modern theory of atoms. Dalton published his first table of relative atomic weights. Six elements appear in this table: hydrogen, oxygen, nitrogen, carbon, sulfur, and phosphorus, with the atom of hydrogen conventionally assumed to weight. -
Five Main Point of Dalton's Atomic Theory
1 Elements are made of extremely small particles called atoms.
2 Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.
3 Atoms cannot be subdivided, created, or destroyed.
4 Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
5 In chemical reactions, atoms are combined, separated, or rearranged. -
William Crookes
In 1861, Crookes discovered a previously unknown element with a bright green emission line in its spectrum and named the element thallium, from the Greek thallos, a green shoot. .During his studies of thallium, Crookes discovered the principle of the Crookes radiometer, a device that converts light radiation into rotary motion. The principle of this radiometer has found numerous applications in the development of sensitive measuring instruments. He also contributed to the study of Cathode Rays -
J.J. Thomson
Thomson’s most important line of work, i, was that which led him in 1897 to the conclusion that all matter, whatever its source, contains particles of the same kind that are much less massive than the atoms of which they form a part. They are now called electrons, although he originally called them corpuscles. His discovery was the result of an attempt to solve a long-standing controversy regarding the nature of cathode rays. -
Thomson's Atomic Model
Sir Joseph John Thomson, who had discovered (1897) the electron, a negatively charged part of every atom. Several alternative models were advanced in the 1900s by Lord Kelvin and others, Thomson held that atoms are uniform spheres of positively charged matter in which electrons are embedded. Popularly known as the plum-pudding model -
Ernest Rutheford
In early work he discovered the concept of radioactive half-life, proved that radioactivity involved the transmutation of one chemical element to another, and also differentiated and named alpha and beta radiation. In 1911, although he could not prove that it was positive or negative,he theorized that atoms have their charge concentrated in a very small nucleus, This was preformed and tested during his gold foil expirement. In his gold foil expirement he projected diffrent radiations io the air. -
Rutheford's Model
Deflections of radiaton, though rare, were found, and proved to be a smooth but high-order function of the deflection angle. It was Rutherford's interpretation of this data that led him to formulate the Rutherford model of the atom in 1911 – that a very small charged nucleus, containing much of the atom's mass, was orbited by low-mass electrons. -
Neils Bohr
Neils Bohr postulated based on quantum theory that electrons travel around an atomic nucleus in a stationary orbit. His work also led to the theory of different energy levels in atoms, that is if an electron drops from a higher to a lower orbit, it must release energy.In the early 1920s, Bohr came up with a way to understand the stability and exactness of atoms using the analogy of standing waves. -
Bohr's Model
In Niels Bohr's model of the atom, electrons can circle the nucleus only in particular orbits of fixed size and energy.The Bohr model and all of its successors describe the properties of atomic electrons in terms of a set of allowed (possible) values. Atoms absorb or emit radiation only when the electrons abruptly jump between allowed, or stationary, states. -
quantum mechanical model
The quantum mechanical model is based on mathematics.The quantum mechanical model is based on quantum theory, which says matter also has properties associated with waves. According to quantum theory, it’s impossible to know the exact position and momentum of an electron at the same time. This is known as the Uncertainty Principle.The quantum mechanical model of the atom uses complex shapes of orbitals (sometimes called electron clouds), volumes of space in which there is likely to be an electron -
James Chadwick
Sir James Chadwick was an Engllish physicist. Before it was believed that the atoms was composed of a nucleus, protons and electrons. With his partner, Rutheford, they hypothesized taht a nuclear particle with no electrical charge also made up an atom. After only two weeks of reaserch his hypothesis was confirmed and in May 1932 he published The Existence of a Neutron. This discovery was very important for the development of the atom. -
James Chadwick Atomic Model
James Chadwick's atomic model consits of a nucleus, protons, electrons and neutrons.
