Chemistry Jacqueline P. Hancock, B.S. M.Ed Quantum Theory Part 2 Chemistry Jacqueline P. Hancock, B.S. M.Ed

Quantum Theory Allows us to predict and understand the role e- play in chemistry 1. How many e- are in a particular atom?? 2. What energies do individual e- possess? 3. Where in the atom are e- found?

Macroscopic View Molecules behave like rebounding balls Does not explain the stability of atoms and the forces that hold them together Properties of atoms are not governed by the same law as larger materials

Max Planck German physicist-(1858-1947) 1900 he discovered that atoms and molecules emit energy only in discrete quantities that he called quanta. He did this while analyzing data on radiation emitted by solids heated to various temps. Nobel Prize in Physics(1918) for Quantum Theory

What is a wave? To understand Quantum Theory we must understand the nature of a wave… Wave is a vibrating disturbance through which energy is transmitted. 2 Types of Waves Transverse Wave Longitudinal Wave

Transverse Waves The medium moves at right angles to the direction the wave travels. The waves are traveling transverse or across the medium

Parts of a Transverse Wave

Longitudinal Waves The medium is moved parallel to the direction that the waves are traveling. Example: The coils in a spring move back and forth in the same direction as the wave travels

Parts of a Longitudinal Wave

Wavelength λ (lambda)- distance between identical points on successive waves......LENGTH Frequency υ (nu) # of waves that pass a particular point in 1 second. SI unit is the Hertz (Hz) 1 Hertz 1 Hz 1cycle/s 1/s

Amplitude- is the vertical distance from the midline of a wave to the peak or trough.

Wave speed formulas u = λ·υ c = λ·υ Where: υ =frequency λ=wavelength u = speed of wave Use with any wave other than electromagnetic radiation c = λ·υ Where: υ =frequency λ=wavelength c = speed of light c = 2.998x108m/s Must use with EMR

Know your calculator!!!

Practice Calculate the speed of a wave whose wavelength and frequency are 17.4 m and 87.4 Hz, respectively λ = u = λ·υ υ = u =

Calculate the frequency in Hz of a wave whose speed and wavelength are 712m/s and 1.14m respectively.

Write Q & A –left side INB Calculate the speed of a wave whose wavelength and frequency are 3.14x10-31 nm and 32.5x1018 Hz respectively. Calculate the frequency in Hz of a wave whose speed and wavelength are 7.12x1012m/s and 1.14x105m respectively.

Calculate the frequency in Hz of a wave whose speed and wavelength are 7.12x1012m/s and 1.14x105m respectively.

Electromagnetic Radiation 1873 James C. Maxwell proposed visible light consists of electromagnetic waves. Maxwell's Theory--an electromagnetic wave has an electric field and magnetic field. Provides mathematical description of behavior of light.

All EM waves travel at 2.998x108m/s Electromagnetic Radiation is the emission of energy from electromagnetic waves All EM waves travel at 2.998x108m/s Approx. 186,000miles/s in a vacuum 299,800,000m/s 373m/s

ELECTROMAGNETIC WAVES Transverse Wave made up of electric fields and magnetic fields that are oscillating at 90oangles How do they travel?

Electromagnetic Spectrum all ER in order of increasing frequency ROY G BIV

EM Wave Calculations c = λ·υ Where: υ =frequency λ=wavelength c = speed of light c = 2.998x108m/s Must use with EMR

The wavelength of the green light from a traffic signal is centered at 522 nm. What is the frequency of this radiation?

# 14. What is the wavelength of radiation with a frequency of 1 # 14.What is the wavelength of radiation with a frequency of 1.50 x 1013Hz? Does this radiation have a longer or shorter wavelength than red light? #15. What is the frequency of radiation with a wavelength of 5.00x10-8m? In what region of the electromagnetic spectrum is this radiation?

Classical Atomic Theory When you heat solids they will emit radiation over a wide range of wavelengths We know this as: Classical Theory *Atoms and molecules admit or absorb any arbitrary amount of radiant energy.* This was only good to explain short wavelengths and not long ones.

Planck’s Quantum Theory Atoms and molecules emit or absorb only in discrete quantities like small packages or bundles called quanta. Quantum= smallest quantity of energy that can be emitted or absorbed from EM radiation

In 1905 Einstein used the theory to solve the photoelectric effect. * electrons are ejected from surface metals exposed to light of at least a certain minimal frequency. Einstein assumed a beam of light behaved as a stream of particles called photons and said.... E=h•υ

E=h•υ c = λ·υ E=h• c λ E = energy of quantum of energy h= Planck’s constant 6.63x10-34 J •s υ = frequency of light SI Units of quantum of energy is Joule (J) c = λ·υ E=h• c λ

Wave vs. Particle Electromagnetic waves are waves that sometimes behave as a stream of particles. How do we know?

Evidence of Wave Model In 1801 Thomas Young passed a beam of light first through a single slit and then through a double slit. When the light reached a darkened screen there were alternating bright and dark bands The bright bands= constructive interference The dark bands= destructive interference

What did this mean? Interference only occurs with waves Therefore light behaved like a wave.

Evidence of Particle Motion 1905 Albert Einstein determined that light behaved as packets of energy called photons When the photons have enough energy(frequency) they can cause the release electrons(energy) The greater the light frequency-the greater the energy released

Evidence of Particle Model Photoelectric Effect is the emission of electrons from a metal caused by light striking the metal Blue light has a higher frequency than red light so photons of blue light have more energy than photons of red light. Red light will not cause the emission of electrons.

Photoelectric Effect

What does this mean? Removing e requires a light of sufficiently high frequency(high energy) to break them free. Shining a beam of light on a metal surface/shooting a beam of particles(photons) at the metal atoms. If the frequency of photons(h•υ) is equal to the energy binding the e in the metal, then the light will have enough energy to knock e loose. If (h•υ) hv is a higher frequency the e will also acquire kinetic energy

Heinsenberg Uncertainty Principle Impossible to know exactly both the velocity and position of particle at the same time. Schrodinger combined this principle and wave properties to formulate his quantum description of e- in atoms

Atomic Emission Spectrum Later 19 century we found that the amount of radiation energy emitted by an object at certain temperatures depends on its wavelength. Frequencies of light emitted by an element corresponds to a particular “color” and separates in discrete lines.

Emission vs. Absorption

The energy of a photon is 5. 87x10-20J The energy of a photon is 5.87x10-20J. What is it’s wavelength(in nanometers)?

Calculate the energy in joules of a photon with a wavelength of 5 Calculate the energy in joules of a photon with a wavelength of 5.00x104 nm (infrared region).

Calculate the energy in joules of a photon with a wavelength of 5 x10-2 nm (x ray region)