History of the Atom
Storyboard Text
- In 1803, John Dalton drew upon the ancient Greek idea of atoms (the word atom comes from the Greek "atomos" meaning invisible). Atoms of a given element are identical, and compounds are combinations of different types of atoms.+ He recognized that atoms of a particular element differ from other elements.
- -Atoms aren't invisible-They're composed from subatomic particles.
- SOLID SPHEREMODEL
- In 1897, JJ Thomson discovered electrons(which he called "corpuscles"), for which he one a noble prize. He subsequently produced the "plum pudding" model of the atom. It shows the atom as composed of electrons scattered throughout spherical cloud of positive charge. +He recognized electrons as components of atoms.-No nucleus
- PLUM PUDDING MODEL
- In 1911, Earnest Rutherford fired positively charged alpha particles at a thin sheet of gold foil. Most passed through with little deflection, but some deflected at large angles. This was only possible if the atom was mostly empty space, with the positive charge concentrated in the center: the nucleus
- +Released positive charge was localized in the nucleus of an atom.
- NUCLEAR MODEL
- +Proposed stable electron orbits; explained the emission spectra of some elements.
- In 1913, Niels Bohr modified Rutherford's model of the atom by stating that electrons moved around the nucleus in orbit of 6 sizes and energies. Electron energy in this model was quantised; electrons could not occupy values of energy between the 6 energy levels.
- He discovered the Planetary Model
- In 1926, Erwin Schrodinger stated that electrons do not move in set path around the nucleus, but in waves. It is impossible to know the exact location of the electron; instead we have 'clouds of probability' called orbitals, in which we are more likely to find an electron.
- +Shows electrons don't move around the nucleus in orbits, but in clouds where their position is uncertain.
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