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Nobel Prize! Thomson- 1906 Rutherford- 1908 Bohr- 1922 Heisenberg-1932 Dalton did not win the Nobel Prize.
-Dalton's Postulates- All matter is composed of atoms. All atoms of the same element are identical. Compounds are formed by a combination of different atoms in definite ratios. Atoms cannot be created, destroyed or changed during a chemical reaction.
VS
Aristotle
Different atoms have different sizes and shapes. Size, shape, and movement of atoms determine the properties of matter.
Empty space cannot exist. Matter is made of earth, fire, air and water!
Democritus
Isotopes are atoms of the same element that have different numbers of neutron. This contradicts Dalton's postulatate that all atoms of the same element are identical in mass, because different isotopes of the same element have different atomic mass.
-a timeline-
THE ATOM
The Bohr model of the atom is inaccurate because it places the atoms in very precise orbitals going around the nucleus of the atom. However, we now know, as the electron cloud model shows, that the electrons are not confined to these specific orbitals; it is just a general idea of where they might be. However, this model is simpler, and may be taught because the concept is easier to grasp.
Dalton
by Naya Frazier
The Heisenberg Uncertainty Principle states that it is impossible to know precisely both the position and velocity of a particle at the same time.
Protons have a positive charge and reside in the nucleus of the atom. Neutrons have no charge and also reside in the nucleus of the atom. Electrons have a negative charge and reside in orbitals around the nucleus. Lead (Pb) has an atomic mass of 207. Its atomic number is 82, so there are 82 protons and 82 electrons. The remaining mass comes from the neutrons, so there are 125 neutrons.
Thomson
Rutherford
Bohr
J.J. Thomson discovered the electron by experimenting with cathode ray tubes. He proposed that the cathode rays were streams of particles much smaller than the atom which he called corpuscles. Although his hypotheses about the existence of bodies smaller than the atom were initially met with much skepticism, he did discover the subatomic particle, the electron.
While Democritus developed the concept that atoms existed, it wasn’t until thousands of years later that Dalton developed the first useful atomic theory. The models are identical; one indivisible atom with no subatomic particles.
The model now features subatomic particles, electrons. The technology of Thomson's experiments with cathode ray tubes made this discovery possible. Thomson proposed that the atom was a positively charged mass with negatively charged electrons evenly distributed without.
Rutherford's model differs from Thomson because it shows the electrons orbiting the nucleus of the atom. The technology of his gold foil experiment led him to this conclusion. (see gold foil experiment bubble) Rutherford's model indicates that the atom is made up of mostly empty space, with a central, positively charged nucleus, orbited by the electrons.
In the Gold Foil experiment, alpha particles were fired at a sheet of gold foil, surrounded by a strip of material coated with zinc-sulfide. While most of the atoms went straight through the foil as expected, some particles were deflected at small and large angles. This disproved the former theory that positive and negative charges were distributed evenly throughout the atom, and lead Rutherford to the conclusion that most of the mass was concentrated in the atoms nucleus, with electrons orbiting the nucleus at a distance. Because the atom was mostly empty space, it made sense that when an alpha particle collided with a gold nucleus, it was deflected.
Matter is composed of atoms, which move through empty space. Atoms are solid, homogeneous, indestructable, and indivisible.
This model differs from the Rutherford model because, while they both show the electrons orbiting the nucleus, the Bohr model features multiple orbitals
