Electrons in Atoms October 20, 2014 Table of Contents Electrons in Atoms > Light and Quantized Energy > Quantum Theory and the Atom > Electron Configuration 1
Electromagnetic Spectrum Electromagnetic radiation a form of energy that exhibits wavelike behavior as it travels through space Spectroscopy Spectroscopy is the study of the interaction of matter and radiant energy > Radiant energy comes from electromagnetic waves Ex: X rays, gamma rays, radio waves > Method of studying substances that are exposed to some sort of exciting energy 2
Visible Light low energy high energy Red Orange Yellow Green Blue Indigo Violet Long wavelength Short wavelength White light is the combination of all the visible colors of light Review Questions 1. Which would have a longer wavelength: orange or violet? ORANGE 2. Which has more energy: red light or blue light? BLUE 3. Which has more energy: microwaves or x rays? X RAYS 3
Wave Nature of Light Light behaves like a wave > Wavelength (λ ) distance between equivalent points on wave; (m) > Frequency (f) number of waves per second; (Hz, or 1/s or s 1 ) All electromagnetic waves, including visible light, travel at the same speed of c = speed of light= 3.00 x 10 8 m/s c = λν > Where > c = speed of light (3.00 x 10 8 m/s) > λ = wavelength > f = frequency Wave Nature of Light c = λν c = speed of light = 3.00 x 10 8 m/s λ = wavelength f = frequency As you can see from the equation, wavelength and frequency are inversely related In other words, as one quantity increases, the other decreases 4
Wave Nature of Light Example: What is the wavelength of a microwave having a frequency of 3.44 x 109 Hz? Substitute c and the microwave s frequency, ν, into the equation. Note that Hz is equivalent to 1/s or s 1 c = λν 3.00 x 10 8 m/s = λ (3.44 x 109 1/s) Divide the values to determine wavelength, λ, and cancel units as required c λ ν Wave Nature of Light Wavelength The distance between two similar points on two successive waves Measured in meters (m), centimeters (cm) or nanomenter (nm) *1 nm = 1 x 10 9 m Amplitude The height of the crest or depth of the trough Refers to intensity or brightness of a light Frequency (ν) The number of waves that pass a point per second This is what changes the energy of a wave Hertz (Hz) is a measure of frequency 5
Particle Nature of Light Light also behaves as a particle > The wave model could not explain the emission of different wavelengths at different temperatures, so a new explanation was needed Particle Nature of Light In 1900, the German physicist Max Planck began searching for an explanation. > That is, while light has wavelike characteristics, it also can be a stream of tiny particles, or bundles of energy, called photons (photoelectric effect) 6
Electrons & Light Light (electromagnetic radiation) is a form of energy it acts like a wave and a particle > Caused by exciting electrons jumping energy levels and then returning to original energy level We see different colors of light (wavelengths) depending on how many energy levels electrons move and the amount of energy they possess Electrons & Light As energy is absorbed, the electrons move from their ground state (original energy level) to an excited state (higher energy level) nucleus Initial position energy levels ) ) ) ) ) ) ) 1 2 3 4 5 6 ground state Final position excited state 7
Electrons & Light Electrons are unstable in their excited state, so they return to the ground state by releasing energy During this return, light is emitted! Final position nucleus ground state energy levels Initial position ) ) ) ) ) ) ) 1 2 3 4 5 6 excited state Spectra of Light Emission Spectra A set of frequencies of the electromagnetic waves emitted by atoms of the element > Shows all the wavelengths of light that are emitted > Spectroscope instrument used to see the emission spectra 8
Spectra of Light Spectrums appear as colored lines on the atomic emissions spectrum Each element s atomic emission spectrum is unique and can be used to determine if that element is part of an unknown compound Review Questions 1. TRUE OR FALSE: Each element has its own unique atomic emission spectra TRUE 2. TRUE OR FALSE: Wavelength and frequency are directly related. FALSE 9
Review Questions Which element is the unknown??? strontium Emission of Light In 1900, Max Planck described the emission spectrum of objects that were heated He discovered that matter can only gain or lose energy in small specific amounts called quanta > Planck s research, along with the work of Heisenberg, Schrödinger, Einstein, etc. gave birth to the field of quantum mechanics, which quantitatively describes the behavior of atoms and subatomic particles 10
Emission Of Light Quantum minimum amount of energy that can be gained or lost by an atom; can be referred to as a packet of energy Photon packet of light energy (quantum) To calculate the energy in a photon: E = h ν Where: E = h ν E = energy in Joules (J) h = Planck s constant 6.626 x 10 34 J s ν = frequency in Hertz (Hz, s 1, or 1/s) Particle Nature of Light Example Problem: Calculate the energy of a light that has a frequency of 7.23 10 14 1/s. E = hv (6.626 10 34 J s) (7.23 10 14 1/s) E = 4.79 10 19 J 11
Wave Particle Duality Electrons have a waveparticle duality > Describes the wave properties of matter, specifically, the wave nature of the electron > de Broglie suggested that particles can exhibit properties of waves 12