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•Rutherford’s model -Shows where protons & neutrons are -Not good at showing the location of electrons •When elements are heated, they are excited & jump up to a higher energy level. In doing so, they give off a color of light. •Each element gives off a unique color called its atomic emission spectrum. •The electrons are what give each element their unique color. •Light gives us a clue to how electrons are arranged. •Light behaves like a wave & like a particle. •Light in wave form is called an electromagnetic wave, & is part of the electromagnetic spectrum which includes x-rays, TV waves, microwaves, radio waves, UV waves & gamma waves. Trough – low points Crest – high points Amplitude – max displacement from equilibrium (middle of wave). Wavelength – the shortest distance between points in which a wave repeats itself. (crest to crest or trough to trough) symbol - λ Parts of a Wave length •Wavelength crest to a crest or trough to a trough lambda •Symbol = λ ( ) meters •Measured in of one wave, from a •Frequency- number of waves that pass a point in 1 second •symbol = v ( ) nu •Measured in Hertz (Hz) •All EM radiation travels at the speed of light, c = 3.00 x 108 m/s in the vacuum of space •Formula: c = λ v c is constant speed of light v is frequency λ is wavelength Microwaves are used to transmit information. What is the wavelength of a microwave having a frequency of 3.44 x 109 Hz? Known Unknown v= 3.44 x 109 Hz c = 3.00 x 108 m/s λ= ? m c = λv λ= c/v • λ= 3.00x 8 10 / 3.44 x • Answer: 8.72 x 9 10 -2 10 m What is the frequency of green light, which has a wavelength of 4.90 x 10-7m An X ray has a wavelength of 1.15 x 10-10m. What is the frequency? •Light as a particle is called a photon. •Light is like a particle because there are only certain amounts of energy it can have. •The minimum amount of energy a photon can have is called a quantum. •Max Planck found that this energy could be calculated with the formula E=hν •E is energy, measured in Joules (J) •h is Planck’s Constant = 6.626 x 10-34 Js •v is frequency (Hz or 1/s) •Once the minimum amount of energy is calculated, the actual energy can be a multiple of the quantum amount. (1x E, or 2 x E, or 3 x E....) Water drops in the air disperse the white light of the sun into a rainbow. What is the energy of a photon from the violet portion of the rainbow if it has a frequency of 7.23 x 1014Hz? Known v = 7.23 x 1014 s-1 Unknown Ephoton = ? J h = 6.626 x 10-34 J s Ephoton= (6.626 x 10-34J s)(7.23 x 1014 s-1) • Cancel the units • Answer: 4.79 x 10-19J What is the energy of each of the following types of radiation? a. 6.32 x 20 -1 10 s b. 9.50 x 10 13 Hz c. 1.05 x 10 16 s-1 •Electrons (called photoelectrons) are emitted from a metal’s surface when light of a certain frequency shines on the surface. •Example: calculators. •Photoelectric cells convert light into electric energy •Niels Bohr in 1913 proposed a quantum model for the hydrogen atom which correctly predicted the frequencies of the lines (colors) in hydrogen’s atomic emissions spectrum. •His model gave atoms only certain allowable energy states. •The lowest state is called the ground state. •When an atom gains energy it is said to be in an excited state. •Bohr also said that the motion of the electron relates to its energy state. That electrons move around the nucleus in certain allowed circular orbits. •The smaller the orbit, the lower the energy state. •Bohr assigned each energy level a quantum number, n. •There are only 7 energy states. •The 7 energy states are like rungs on a ladder, electrons can move up or down the ladder from rung to rung, but there is no “in between”. •An electron can only move from one allowable orbit to another and can only emit or absorb certain amounts of energy. The 1st energy level can hold only 2 e-, 2nd 8e-, 3rd 8e-, 4th 18e-, 5th 18e-, 6th 32eremember these #’s 2-8-8-18-18-32! Ex: Draw the Bohr model for Fluorine # of Protons = 9 # of neutrons = 10 # of Electrons = 9 ee-e- enucleus e- e-ee- e- Draw the Bohr Model for Ni • # of e- = 1st level = 2e2nd level = 8e3rd level = 8e4th level = 10e- 28 e- e- eee- e- eeeeeee-e-e- nucleus e- e-eeeeeeeeeee- Draw the Bohr model for the following elements: Co F Br Ag