The Development of a New Atomic Model. Objectives Explain the mathematical relationship between the speed, wavelength, and frequency of electromagnetic.

The Development of a New Atomic Model

Objectives

Explain the mathematical relationship between the speed, wavelength, and frequency of electromagnetic radiation.Discuss the dual-wave particle nature of light.Discuss the significance of the photoelectric effect and the line-emission spectrum of hydrogen to the development of the atomic model.Describe the Bohr model of the hydrogen atom.

Links

http://www.quantumintro.com/

http://newton.ex.ac.uk/research/qsystems/people/jenkins/mbody/mbody2.html

A New Model Was Formed

Why wasn’t the positive nucleus attracted to the negative electron cloud?

Investigations into light led to understanding of relationship between light and electrons.

Led to revolutionary theory about the nature of light, matter, and atoms

Properties of Light

Electromagnetic spectrumElectromagnetic spectrum—all forms of radiation exhibit wavelike behavior as they travel through space.

γ-rays (gamma), X-rays, ultraviolet, visible light, infrared light, microwaves, radio waves

Travel at 3.0 x 108 m/s

www.yorku.ca/ eye/spectru.htm

Waves

WavelengthWavelength—λ (lambda)—distance between crests of adjacent waves (nanometers 1 nm=1 x 10-9 m)FrequencyFrequency—ν (nu)—the number of waves that pass a given point in one second (Hz—hertz)Speed of lightSpeed of light—wavelength is inversely proportional to frequency

c = λ ν

Photoelectric Effect

Electrons are given off from a metal when light of a certain frequency is shined on itIf light is a wave, light of any frequency should make electrons be given off??why only certain frequencies??

Light as Particles

Max Planck—German physicist—1900

Proposed that objects give off energy in small, specific amounts

QuantumQuantum—minimum quantity of energy that can be lost or gained by an electron

http://nobelprize.org/physics/laureates/1918/planck-bio.html

Albert Einstein

Electromagnetic radiation is both a wave and a particle—dual wave-particle naturedual wave-particle natureLight has wavelike propertiesLight can behave as a stream of particles—each particle with a quantum of energyPhotonsPhotons—particle of electromagnetic radiation having zero rest mass and carrying a quantum of energyAmount of energy depends on frequency

http://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Einstein.html

Line-Emission Spectrum

Ground stateGround state—lowest energy state of an atom

Excited stateExcited state—state where an atom has higher potential energy

Neon sign—current passes through a gas at low pressure and is excited—when it returns to ground state it gives off energy as electromagnetic radiation

http://www.neonsign.com/brands/index.html?item=ready

Line-Emission Spectrum

When light from an excited state atom is passed through a prism, it is separated into a series of specific wavelengths (not all like a rainbow)When an atom falls back from excited state to ground state—it gives off a photon of radiationLed to Quantum TheoryQuantum Theory

Line-Emission SpectrumSpecific lines in spectrum mean that the energy differences between energy states was fixed

Electrons exist only in specific energy states

http://www.glencoe.com/sites/common_assets/science/cmc/cim/animations/ch5_1.rm

Animation of H line spectrum

http://www.quantumintro.com/

Bohr Model

Neils Bohr—Danish physicist—1913Linked model of atom with the emission spectrumElectrons can only travel in specific paths (orbits)Electrons in an orbit have a fixed amount of energyOrbits closest to nucleus have smallest energy

http://nobelprize.org/physics/laureates/1922/bohr-bio.html

Bohr ModelAtoms gain energy & electrons move to higher orbits (excited state)

As electrons fall back to lower energy orbits they give of photons with a fixed amount of energy

Amount of energy photon has is seen as lines in emission spectrum