Atomic Models: Developing the Structure of the Atom.
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Atomic Models:Developing the Structure
of the Atom
Atomic Models:Developing the Structure
of the Atom
The Greek ModelThe Greek Model Around 440 BC, Leucippus originated the
atom concept. He and his pupil, Democritus, refined and extended it in future years.
Five major points to their atomic idea. – All matter is composed of atoms, bits of matter too
small to be seen. These atoms CANNOT be broken apart
– There is a void (empty space) between atoms– Atoms are completely solid– Atoms of different materials are different in size,
shape, and weight
Around 440 BC, Leucippus originated the atom concept. He and his pupil, Democritus, refined and extended it in future years.
Five major points to their atomic idea. – All matter is composed of atoms, bits of matter too
small to be seen. These atoms CANNOT be broken apart
– There is a void (empty space) between atoms– Atoms are completely solid– Atoms of different materials are different in size,
shape, and weight
The Dalton Model (1803)The Dalton Model (1803) John Dalton of England introduced the
atomic idea to “Modern” chemistry The basic ideas in Dalton's atomic theory:
– Chemical elements are made of atoms – The atoms of an element are identical – Atoms of different elements have different
masses – Atoms only combine in small, whole number
ratios such as 1:1, 1:2, 2:3 and so on.
John Dalton of England introduced the atomic idea to “Modern” chemistry
The basic ideas in Dalton's atomic theory:– Chemical elements are made of atoms – The atoms of an element are identical – Atoms of different elements have different
masses – Atoms only combine in small, whole number
ratios such as 1:1, 1:2, 2:3 and so on.
Dalton’s Atom, 1807Dalton’s Atom, 1807
The atom is a solid indivisible sphere that can undergo chemical reactions but is unchanged by the reaction.
The Thomson Model,1903 The Thomson Model,1903 In 1897, J.J. Thomson discovered
the first subatomic particle, the electron, using a cathode ray tube.
First model showing an atom that is divisible (has smaller parts).
In 1897, J.J. Thomson discovered the first subatomic particle, the electron, using a cathode ray tube.
First model showing an atom that is divisible (has smaller parts).
Plum Pudding Model
The nucleus was discovered.
The Gold Foil Experiment
The Rutherford ModelThe Rutherford Model1. The atom contains a tiny dense center:
“nucleus” – the nucleus is about 1/10 trillionth the volume of
the atom
2. The nucleus contains almost the entire mass of the atom.
3. The nucleus is positively charged.
4. The electrons move around in the empty space (the void?) surrounding the nucleus
1. The atom contains a tiny dense center: “nucleus” – the nucleus is about 1/10 trillionth the volume of
the atom
2. The nucleus contains almost the entire mass of the atom.
3. The nucleus is positively charged.
4. The electrons move around in the empty space (the void?) surrounding the nucleus
Rutherford’s Atom1908
Rutherford’s Atom1908
3p+
e-
e-
e-
The Bohr Model (1913)The Bohr Model (1913) Niels Bohr applies
mathematics to Rutherford's model. This eventually led to the idea of energy levels for the electrons.
Led scientists to the understanding that valence electrons, those in the highest energy level, determine chemical reactivity.
Niels Bohr applies mathematics to Rutherford's model. This eventually led to the idea of energy levels for the electrons.
Led scientists to the understanding that valence electrons, those in the highest energy level, determine chemical reactivity.
Chadwick (1935)Chadwick (1935)
Hypothesized that the mass of the nucleus could not be explained by the masses of protons alone.
Be foil experiment discovered neutrons, particles that had mass but no charge.
Hypothesized that the mass of the nucleus could not be explained by the masses of protons alone.
Be foil experiment discovered neutrons, particles that had mass but no charge.
Subatomic ParticlesSubatomic Particles
3 protons
4 neutrons
3 electrons
Lithium
Particle Charge Mass (kg) LocationProton 1 1.67E-27 nucleus
Neutron 0 1.67E-27 nucleus
Electron -1 9.11E-31moving around the
outside of the nucleus
Chemical versus Nuclear ReactionsChemical versus Nuclear Reactions
Chemical NuclearStable atoms (Not radioactive)
Electrons exchanged between atoms
Atoms are conserved (unchanged but rearranged)
Reactions are affected by temperature and pressure
Radioactive nuclei = unstable, which decays
Nucleus ejects/absorbs neutrons, protons, electrons.
Atoms change into new elements/isotopes! Atomic # or mass # changes
Reactions NOT affected by temperature or pressure.
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