Valence Shell Electron Pair Repulsion (VSEPR) Theory The Modern Atom: Valence Shell Electron Pair Repulsion (VSEPR) Theory

What is light? Light is how we refer to electromagnetic radiation. Applies to all types of light: Infrared Light UV light Microwaves Radio Waves X-Rays

What are the properties of Light? Light is a WAVE! Normally we think of light as being made of little particles that leave a light source like a bullet leaves a gun…NOT the CASE! Light is characterized by its wavelength and frequency.

What is wavelength? (λ)

What is frequency? (V) The number of times that light “waves” each second. Units = Hertz (Hz)

How are frequency and wavelength related? λ*V = C C is the speed of light in a vacuum 3.00 x 108 m/s

Energy of Light is related to its FREQUENCY! E = h*v , where…. E = the energy of light (Joules, J) h = Planck’s constant = 6.626 x 10-34 J*s V = frequency (Hertz, Hz) Light with a frequency of 450 Hz has an energy of 3.0x10-22 J.

Light is quantized! When something is quantized, this means that it can exist only at certain points. Example: Increasing altitude.

So what does all this have to do with the Atom??? People began to notice that different elements gave off different colors of light when heated (Spectra) The process is now called today: Spectroscopy

This led to…Bohr’s Planetary Model!!!

Emission of different colors of light  2 different states Ground State: When an atom is at rest, each electron lies in its lowest possible energy orbital. Excited State: When energy is added to an atom the electrons absorb it and jump to a higher energy orbital. When the electron loses its energy, light is emitted.

Diagram of Energy States

Spectroscopy: Identify via element’s spectra! Continuous spectrum: Looks like a rainbow and contains all energies of light Line Spectrum: spectra given off by an element…the energy given off creates visible lines of different colors when using a spectrometer.

How to do spectroscopy… Add energy to a sample. Measure the light given off when the electrons return to ground state. Compare the emitted light to the spectra of known elements.

How to do Spectroscopy…

Different Types of Spectroscopy UV-Visible Light Spectroscopy Infrared Spectroscopy Nuclear Magnetic Resonance Spectroscopy

Things about Bohr’s Model Good vs. Bad It explains the existence of line spectra It explains the findings from the gold foil and cathode ray tube experiements The orbital energy predictions ONLY worked for Hydrogen.

Electromagnetic Radiation Seven parts Longest (λ) to shortest Radio waves Micro waves Infrared Visible light Ultra violet light X – rays Gamma rays Greatest (ν) to smallest Chapter 13

Spectrum of Colors Visible light (7 parts) Longest (λ) to shortest Red Orange Yellow Green Blue Indigo Violet Greatest (ν) to smallest Chapter 13

Section 12.7: The Quantum Concept Objective: Why metals change color when heated? 1900s, German physicist Quantitatively Color changes occur with small discrete energy changes The amount of radiant energy (E) absorbed / emitted is proportional to the frequency (ν) of radiation Formula for amount of energy ( E) = h x ν Planck’s constant = h = 6.6262 x 10-34 J s Chapter 13

Calculate the amount of energy absorbed when the wave length is equal to 5.0 x 10-8 m. Calculate the amount of energy emitted from the southern lights, if the wave length is equal to 3.5 x 10-7m. Chapter 13