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John Dalton
(Photo-Atoms represented as spheres) John Dalton was the first person to propose that elements consisted of atoms and that compounds were atoms formed by different elements combined. • Analogised atoms were like invisible and indestructible building blocks
• Stated that all compounds were composed of combinations of these atoms in defined ratios
• Postulated that the rearrangement of the reacting atoms were by the results of chemical reactions
• All atoms of an element are identical but vary in size and mass -
Dmitri Mendeleev
(Photo-Periodic Table) Dmitri Mendeleev arranged elements into 7 groups and discovered that the properties of elements were periodic functions of their atomic weights at which then created The Periodic Table/Law. • Saw that atomic weight was important when categorizing
• Fell asleep when trying to arrange the elements and saw in a dream all the elements fall into place
• Propose that some of the elements, whose behavior did not agree with his predictions, must have had their atomic weights measured incorrectly. -
Albert Einstein
(Photo-E=mc² explained) Albert Einstein published the famous equation E=mc² (Energy = Mass + Speed of Light squared). • The reason for 'c' was because the speed of light was constant
• Einstein proved the existence of atoms by analysing the phenomenon of Brownion motion -
R.A. Millikan
(Photo-Electron) An oil drop experiment had influenced R.A. Millikan to determine the charge (e=1.602 x 10 -19 coulomb) and the mass (m = 9.11 x 10 -28 gram) of an electron. • The experiment entailed balancing the downward gravitational force with the upward drag and electric forces on tiny charged droplets of oil suspended between two metal electrodes.
• Using a known electric field, it was proved possible to determine the charge on oil droplets in mechanical equilibrium -
Ernest Rutherford
(Photo-Nucleus) Ernest Rutherford established that the nucleus was very dense,very small and positively charged. • Discovered the nucleus by an experiment called the Gold foil experiment
• Proposed a charged particle could only be achieved if most of the mass and charge were concetrated in a very small central body
• Believed the nucleus had a negative charge but concluded it didn't matter if it was positive or negative; it would not affect the calculations -
Niels Bohr
(Photo-Bohrium Atomic Structure) Niels Bohr developed an explanation of atomic structure that underlies regularities of the periodic table of elements. • Presented an Atom as a small, positively charge nucleus surrounded by orbiting electrons
• Discovered that electrons travel in seperate orbits around the nucleus and that the number of electrons in the outer orbit is determined by the atomic no.
• The chemical element Bohrium is named after him
• An electron can be viewed in 2 ways: particle or wave, but never the same time
