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400
Democritus- Greece c.400BCE
- believed atoms can combine as they have different shapes
- believed everything is either made up of space or atoms
- thought that atoms determine properties, e.g. edges of atoms
lead to the differences in taste and colour of substances - thesis not based on scientific evidence, but attempted to explain the concept of an atom and how atoms form the physical world
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Period: 400 to
Tracing the history of Atomic models
Please note that the year 400 is c. 400 BCE, -
Newton- England
- provided the basis for later atomic theory research: allow
many later theories to be built upon his Laws of Motion, theory of gravity, etc. - Suggested a mechanical universe with small solid masses in motion
- Law of Gravity states that all matter are pulled together by gravity: allow other scientists to use this in regards to atomic theory- that opposite forces will keep atoms at a certain distance from each other
- provided the basis for later atomic theory research: allow
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Dalton- England
- Experiment: to see how soluble different gases are in water, and found that each dissolve differently- concluded that the gases have atoms of different masses
- Dalton's Atomic Thoery:
- All matter are made of atoms.
- Atoms of the same element are identical.
- Atoms of different elements have different properties &
weights. - Atoms make up compound in simple ratios.
- Atoms are neither created nor destroyed.
- Dalton summarised all the major principles of atomic theory
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G. J. Stoney- Ireland
- found that there must be some fundamental unit of electricity related to atoms
- most important work: calculated the magnitude of electrons
- proposed that the 'electron' is one of the 3 fundamental units; the others are gravity and velocity of light
- laid doundation for the discovery of 'electron' by J. J. Thomson
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J. J. Thomson- England
- through cathode-ray experiment, found negatively charged particles which he called 'corpuscles'.
- found these 'corpuscles' present in all elements
- 'raisin pudding model' his atomic model showed negaticely charged particles distributed evenly among positively charged particles in the atom
- improved our understanding of sub-atomic particles and raised quesitons about the structure of matter
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Planck- Germany
- originator of quantum theory
- explained that energy is released in chunks called 'quanta' and not in a continuous stream
- his discovery of quantum theory transformed our understanding of the world of atoms and sub-atomic structures
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Nagaoka- Japan
- developed a 'Saturnian model' of atom portraying a positively charged particle in the middle surrounded by negatively charged particles like the ring of Saturn
- gave us an general idea of how electrons are arranged in an atom
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Millikan- America (born in NZ)
- through his well-known oil-drop experiment, he found the charge of a single electron
- this discovery allows the calculation of the mass of electorn and the mass of positively charged atoms
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E. Rutherford- America
- through his experiment related to radioactivity, he found that half of the atoms of a radioactive substance would disintegrate, leaving 'half-life' of the matter behind
- through examination of alpha particles, concluded that atoms contain a small nucleus which takes most of the weight, while the rest is empty space where electrons orbit the nucleus
- first person to separate an atomby ejecting the proton
- contribute to our understanding of the structure of an atom and the proton
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H. G. J. Mosely- England
- noted that the lines produced by the X-ray spectra of more than 30 metallic elements move according to atomic weight
- Mosely's Law: founf a relationship between the frequencies of the radiaiton & the atomic no.
- noted that thje atomic no. = positive charge of atom nucleus
- Mosely predicted the properties of several elements in the periodic table & over the years, we were able to slot them in
- he found a vital ilink between the physical make-up and the chemical properties of an element
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Bohr- England (Born in Denmark)
- in Bohr's atomic model, electons only exist in fixed orbits
- suggested that electrons move up or down an orbit when absorbing ro releasing energy
- showed that hte characteristics of an element can be predicted by the electrical configuration of tis atom
- contributed to our understanding of the behaviour of atoms and electrons
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James Chadwick- England
- discovered neutrons
- discovery of neutrons made up for the missing 50% of the mass of the atom
- found that these neutrons with the same weight as protons could force protons out of substances containing hydrogen
- completed our understanding of sub-atomic structure of atom
