atomic models: from hypothesis to theory

Atomic Models:Atomic Models:From Hypothesis to From Hypothesis to

TheoryTheory

http://www.youtube.com/watch?v=bw5TE5o7JtE&feature=BFa&list=PLE2B5C43C0BC88688&lf=results_main

The Greek ModelThe Greek Model440 BC: Leucippus & 440 BC: Leucippus &

Democritus hypothesize Democritus hypothesize that matter is made of that matter is made of atoms atoms

Explained why different Explained why different substances have different substances have different propertiesproperties

Performed no Performed no experimentsexperiments

Very little evidence to Very little evidence to support hypothesissupport hypothesis

Democritus of Abdera

The Greek ModelThe Greek Model Five major pointsFive major points

1.1. All matter is composed of atomsAll matter is composed of atoms too small to be seentoo small to be seen CANNOT be split into smaller partsCANNOT be split into smaller parts

2.2. There is a void, which is empty space between There is a void, which is empty space between atomsatoms

3.3. Atoms are completely solidAtoms are completely solid

4.4. Atoms are homogeneous, with no internal structureAtoms are homogeneous, with no internal structure

5.5. Atoms are different in size, shape, and weightAtoms are different in size, shape, and weight

The Dalton ModelThe Dalton Model

1803: John Dalton (England) 1803: John Dalton (England) re-introduced the atomic idea re-introduced the atomic idea to modern chemistry to modern chemistry

Dalton and other chemists Dalton and other chemists did experiments involving did experiments involving gases and how they combinegases and how they combine

They noticed that elements They noticed that elements always seemed to combine always seemed to combine in the same ratios (in the same ratios (such as such as 1:1, 1:2, 2:3 etc)1:1, 1:2, 2:3 etc)

DaltonDalton’’s Atom, 1807s Atom, 1807 To explain these observations, Dalton To explain these observations, Dalton

hypothesized that:hypothesized that: Chemical elements are made of atoms Chemical elements are made of atoms The atoms of the same element have the same The atoms of the same element have the same

massmass Atoms of different elements have different Atoms of different elements have different

masses (but the same general shape)masses (but the same general shape) Atoms are involved in chemical reactions but are

not changed by them Characteristics of Dalton’s atom

uniformly dense indivisible solid spheres

The Thomson ModelThe Thomson Model1897: J.J. Thomson hypothesized that 1897: J.J. Thomson hypothesized that

there are areas of negative charge there are areas of negative charge (electrons) within the atom(electrons) within the atom

Based on experimental observationsBased on experimental observationsCalled the Plum Pudding ModelCalled the Plum Pudding Model

Discovery of the ElectronDiscovery of the Electron

http://www.youtube.com/watch?v=IdTxGJjA4Jw

RutherfordRutherford’’s Gold Foil Experiments Gold Foil Experiment Rutherford shot alpha particles at gold foil expected the alpha particles to go through the gold

foil but be deflected- most particles did Some alpha particles weren’t deflected, they

bounced back! He said “It was almost as incredible as if you fired a

15-inch shell at a piece of tissue paper and it came back and hit you."

The Rutherford Model, 1911The Rutherford Model, 1911 Atomic theory was revised to explain RutherforAtomic theory was revised to explain Rutherfor

dd’’s observations s observations RutherfordRutherford’’s Model stated:s Model stated:

The atom contains a tiny dense center called the The atom contains a tiny dense center called the nucleus nucleus

the volume of the nucleus is about 1/10 trillionth the the volume of the nucleus is about 1/10 trillionth the volume of the atom volume of the atom

The nucleus is essentially the entire mass of the The nucleus is essentially the entire mass of the atom (the rest is mostly empty space)atom (the rest is mostly empty space)

The Rutherford Model, 1911The Rutherford Model, 1911

RutherfordRutherford’’s Model stated:s Model stated:The nucleus is positively chargedThe nucleus is positively chargedThe amount of positive charge of the nucleus The amount of positive charge of the nucleus

balances the negative charge of the electrons balances the negative charge of the electrons The electrons move around in The electrons move around in

the empty space of the atom the empty space of the atom

surrounding the nucleussurrounding the nucleus 3p+

e-

e-e-

Discovery of the NucleusDiscovery of the Nucleus

http://www.youtube.com/watch?v=wzALbzTdnc8 http://www.youtube.com/watch?v=wzALbzTdnc8

The Bohr ModelThe Bohr Model

Niels Bohr Niels Bohr applies quantum theory to applies quantum theory to

Rutherford's atomic structureRutherford's atomic structure led to the idea of electrons led to the idea of electrons

moving around the nucleus in moving around the nucleus in orbits or energy levelsorbits or energy levels

emission of light occurs when emission of light occurs when an electron moves into a an electron moves into a lower energy orbit.lower energy orbit.

BohrBohr’’s Researchs Research Electron orbit around the nucleus in seven different Electron orbit around the nucleus in seven different

energy levels, or shells. energy levels, or shells. Electrons would only occupy the lowest possible Electrons would only occupy the lowest possible

energy level.energy level. Electrons would only move up a level (increasing Electrons would only move up a level (increasing

energy) if the lower levels were full.energy) if the lower levels were full.

Atomic ScaleAtomic Scale

Modern Atomic TheoryModern Atomic Theory

An updated version of BohrAn updated version of Bohr’’s models modelElectrons move in 3-D clouds rather than Electrons move in 3-D clouds rather than

orbitsorbitsThere are three There are three

types of particles types of particles

in the atom rather in the atom rather

than twothan two

Subatomic ParticlesSubatomic ParticlesParticle Particle ChargeCharge Mass (kg)Mass (kg) Relative Relative

MassMassLocationLocation



ProtonProton

NeutronNeutron

ElectronElectron



ProtonProton 11

NeutronNeutron

ElectronElectron



ProtonProton 11

NeutronNeutron 00

ElectronElectron



ProtonProton 11

NeutronNeutron 00

ElectronElectron -1-1



ProtonProton 11 1.67x101.67x10-27-27 11

NeutronNeutron 00 1.67x101.67x10-27-27

ElectronElectron -1-1 9.11x109.11x10-31-31



ProtonProton 11 1.67x101.67x10-27-27 11

NeutronNeutron 00 1.67x101.67x10-27-27 11

ElectronElectron -1-1 9.11x109.11x10-31-31



ProtonProton 11 1.67x101.67x10-27-27 11


ElectronElectron -1-1 9.11x109.11x10-31-31 00



ProtonProton 11 1.67x101.67x10-27-27 11 NucleusNucleus






NeutronNeutron 00 1.67x101.67x10-27-27 11 NucleusNucleus





NeutronNeutron 00 1.67x101.67x10-27-27 11 NucleusNucleus

ElectronElectron -1-1 9.11x109.11x10-31-31 00 outside outside nucleusnucleus

http://abyss.uoregon.edu/~js/http://abyss.uoregon.edu/~js/21st_century_science/lectures/lec05.html21st_century_science/lectures/lec05.html

http://dl.clackamas.edu/ch104-04/daltonhttp://dl.clackamas.edu/ch104-04/dalton%27s.htm%27s.htm

http://abyss.uoregon.edu/~js/http://abyss.uoregon.edu/~js/21st_century_science/lectures/lec11.html21st_century_science/lectures/lec11.html

http://galileo.phys.virginia.edu/classes/http://galileo.phys.virginia.edu/classes/252/Rutherford_Scattering/252/Rutherford_Scattering/Rutherford_Scattering.html Rutherford_Scattering.html

atomic models: from hypothesis to theory

Documents

dalton model

atoms chemical elements

theory slide

weight slide

plum pudding model slide

thomson model

greek model

rutherford model