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John Dalton(1766–1844)
He hypothesised that the atom was the smallest particle of matter and that atoms could not be recreated or destroyed. Some evidence he based this upon was the weight of each individual atom compared to the lightest atom of hyrdrogen. Hyrdorgen is the first element on the periodic tale it has an atomic number of 1 meaning 1 proton which counts for half the majority of its overall weight. He assigned a weight to atoms such as oxygen,carbon and nitrogen by using his results from chemical analysis. -
J.J Thomson
He discovered the electron, using properties of cathode rays. Cathode rays meaning, glowing beams of light passing through a high vacuum tube.Thomson interpreted the deflection of the rays as smaller then an atom. He was the first person to ever discover the electron. He was able to identify the physical existence of electrons inside of an atom. This meant that in fact atoms were not visible and could be seen. His theory also suggested that atoms had a positive charge and were spherical shaped. -
Marie Sklodowska Curie
Marie had a fascination with rays that were recently discovered by a precious scientist. She conducted several experiments in the science lab with her husband and they soon discovered that the substance pitchblende. She evaluated, due to the strong rays being emitted that it was made up of radioactive elements polonium and radium. The curies came up with the term “radioactivity" to describe elements that emitted strong and powerful rays. -
Ernest Rutherford
Structure of an atom developed. He worked out a nuclear model of the atom in which almost all of the mass of an atom is concentrated in a very small nucleus. He established an initial theory describing that the atom had a positive nucleus surrounded by orbiting electrons. He came to conclusions after he conducted the gold foil experiment".He used a thin layer of gold and shot alpha particles through it. The particles went through the foild proving the gold atom was made of mainly empty space. -
Niels Bohr
His mentor was Ernest Rutherford, who had already theorized that atoms consisted of a single nucleus. He improved his theory by regarding paths that the electrons followed. He developed an explanation of the atomic structure that showed the consistency of the periodic table of elements. He created an atomic model displaying the ideas, that demonstatedatoms built up of successive and consecutive layers of orbiting shells of electrons. He stated that the ouer shell could hold more electrons. -
J.J Thomson
Thomas also takes the credit for discovering the first ever existence of isotopes of a stable element. Isotopes refers to any two or more forms of a chemical element , in which they have the same number of protons in the nucleus or the same general atomic number, but with a different number of neutrons in the nucleus and an overall different atomic weight. -
Henry Moseley
Henry Mosley first used X-Rays to study elements' structures, but became well known for Moseley’s law, which advanced chemistry in a way in which elements were sorted in logical order in accordance to the number of protons they have in their nucleus. This lead to a more precise understanding and an accurate understanding of each element and its position on the periodic table. Knowing that the number of protons corresponds to the atomic number of an element. -
Francis Aston
He made a very significant discovery to atomic science in his invention of the "Mass Spectrograph". The device has the capability to separate isotopes by measuring the minute differences between masses, by detecting particles photographically. When he was examining the element Neon, he saw two curves in the photograph, meaing it was made up of two different atoms which are the same chemically, but weighed differently.
Using this device he was able to identify 212 existing isotopes. -
Erwin Shrodinger
Viewed electrons as continuous clouds and introduced "wave mechanics" as a mathematical model of the atom. By using mathematical equations he described the likelihood of finding an electron in a certain position. This atomic model that he created is now known as the the "quantum mechanical" model of an atom. It does not define the position, but rather predicts it. This model can be portrayed as a small nucleus surrounded by a cloud of
electrons. This model then introduced sub-energy levels. -
James Chadwick
Chadwick made an ultimate discovery using alpha particles. Alpha particles meaning a positively chraged particle given off by certain radioactive substances. He discovered the existence of a neutrally charged atomic particle close to the protons within the nucleus. Thus was born the neutron as we have today. This contrasted with the helium alpha particles which are charged and therefore repelled by the electrical forces present. This effectively was the last piece to the atomic puzzle. -
Murray Gell-Mann
United States physicist, noted for his classification of subatomic particles and his proposal of the existence of quarks. Mann proposed the quark model which described that particles could not split. He proposed that sub-atomic particles including neutrons and protons are composed of fundamental building blocks that he named “quarks” consisting of very unique properties holding similar fractional change.They are combined by forces coming
from “gluons”. Also known as the "eightfold way".
