Evolution of Atomic Structure

Dalton 1805

• Billiard Ball Model• Composed of

indestructible, indivisible atoms

• Identical for each element but different from other elements

Thompson 1904

• Raisin Bun Model• Atoms have electrons

embedded in a positive material

Rutherford

Nuclear Model• Atom is composed of a

tiny nucleus and orbiting electrons

• Most of the atom is empty space

• Very small electrons occupy most of the space

• Nucleus is composed of protons and neutrons

Key experiment:Gold Foil Experiment

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf

http://micro.magnet.fsu.edu/electromag/java/rutherford/

Quantum Theory

Hot Body Spectrum

Continuous Spectra?

• Mathematical model’s could not explain the entire distribution of light at the time

• Max Planck surmised that the spectra was not continuous but rather had steps

Photoelectric Effect

• When specific wavelengths of light hit some metals electrons will be displaced

• The intensity of the light did not effect the current produced

• The wavelength of light did effect the current

Bohr Model

Quantized Model Electrons exist in

exact orbits/shells The distance from the

nucleus of each orbit is quantized

Used Balmer’s line spectra

http://www.upscale.utoronto.ca/PVB/Harrison/BohrModel/Flash/BohrModel.html

Types of Spectra

Line

Spe

ctra

Bohr’s Postulates

Bohr’s First PostulateBohr’s First PostulateElectrons do not radiate energy as they orbit the nucleus. Each orbit corresponds to a state of constant energy (called a stationary state).

Bohr’s Second PostulateBohr’s Second PostulateElectrons can change their energy only by undergoing a transition from one stationary state to another.

Quantum Numbers

Principal Quantum Number

• Main Shell

Secondary Quantum Number

• The secondary quantum number relates primarily to the shape of the electron orbit. The number of values for l equals the volume of the principal quantum number.

Magnetic Quantum Number

• The magnetic quantum number, ml, relates primarily to the direction of the electron orbit. The number of values for ml is the number of independent orientations of orbits that are possible.

• Values of ml range from –l to +l

Spin Quantum Number

• The spin quantum number, ms, relates to a property of an electron that can best be described as its spin. The spin quantum number can only be 1/2 or1/2 for any electron.

p. 162 – 184

p. 166 # 1-6, 11

p. 173 #1-5

p. 180 # 1-4, 7, 9, 10

p. 184 # 1-6