3Models of the AtomSo far, the model of the atom consists of protons and neutrons making up a nucleus surrounded by electrons. After performing the gold foil experiment, Rutherford hypothesized a model of the atom that looked much like the one below.
4What about the electrons?? Rutherford didn’t know exactly where the electrons were located in the atom, just that they surrounded it, or why chemical bonding occurred.Bohr figured out that electrons orbit in energy levels around the atom.
5The Bohr ModelNiels Bohr ( ) was a student of Rutherford and believed the model needed improvement.Bohr proposed that anelectron is found only inspecific circular paths, ororbits, around the nucleus.(write this in before “However, this model….”)
6Models of the AtomHowever, this model could not explain the chemical and physical properties of the elements.
71. why metals give off certain colors when heated in a flame -or- Models of the AtomFor example it could not explain:1. why metals give off certain colors when heated in a flame or-2 .why objects heated to high temperatures first glow dull red, then yellow, then white
9Light is all about the Electrons! Light is a form of electromagnetic radiation that travels like a wave through space as PHOTONS.When electrons get excited, they jump up to higher energy levels and then fall back downDepending on how high they jump, they will give off a different color of LIGHT
11Atomic Emission Spectra excited stateENERGY INPHOTON OUTGAIN energyLOSE energyground state
12Energy of ElectronsWhen atoms are heated, bright lines appear called line spectraAn electron absorbs energy to “jump” to a higher energy level. (excited)When an electron falls to a lower energy level, energy is emitted. (ground level state)
14Atomic Emission Spectra Every element has a UNIQUE emission spectrum. The colors that you see represent the element’s electrons jumping through the energy levels!LONG JUMPS are represented by HIGH energy colors (violet & blue)SHORT JUMPS are represented by LOW energy colors (red).
16EM Spectrum HIGH ENERGY LOW ENERGY R O Y G. B I V red orange yellow greenblueindigoviolet
17Properties of LightMovement of excited electrons to lower energy levels, and the subsequent release of energy, is seen as light! Before 1900, scientists thought light behaved solely as a wave. This belief changed when it was later discovered that light also has particle-like characteristics. This is called the wave-particle duality of light.
18First, Let’s look at the WAVE nature of light Light as a WAVE
19Wave PropertiescresttroughLesser frequencyAgreater frequency
20Properties of LightThe significant feature of wave motion is its repetitive nature, which can be characterized by the measurable properties of wavelength and frequency.
21Waves Wavelength () - length of one complete wave Frequency (f) - # of waves that pass a point during a certain time periodhertz (Hz) = 1/s
22Properties of LightElectromagnetic radiation is a form of energy that exhibits wavelike behavior (wavelength, frequency, ect) as it travels through space. Together all forms of electromagnetic radiation form the electromagnetic spectrum.
23On the electromagnetic spectrum, the lowest energy waves (longest wavelength and lowest frequency) are radio waves. The highest energy waves (shortest wavelength and highest frequency) are gamma rays.
24FREQUENCY and WAVELENGTH are INVERSELY proportional. (f ↑ ↓) ENERGY and FREQUENCY are DIRECTLY proportional. (E↑ f ↑)
25Now, let’s look at the PARTICLE nature of light Light as a PARTICLE
26Properties of LightIn the early 1900’s, scientists conducted experiments involving interactions of light and matter that could not be explained by the wave theory of light.
27Properties of LightOne experiment involved a phenomenon known as the photoelectric effect. The discovery of the photoelectric effect led to the description of light as having both wave and particle properties.
29c = f EM Spectrum c: speed of light (3.00 108 m/s) Frequency & wavelength are inversely proportionalc = fc: speed of light (3.00 108 m/s): wavelength (m, nm, etc.)f: frequency (Hz)
30Example 1If the frequency of a wave is 500 hz, what is the wavelength? C = λf C = 3.0 x 108 m/s f = 500 hz λ = ? 3.0 x 108 = 500 x λ λ = 600,000 m One sig fig or 6 x 105
31Quantum TheoryThe energy of a photon is proportional to its frequency.E = hfE: energy (J, joules)h: Planck’s constant (6.626 J·s)f: frequency (Hz)
32Example 2What is the energy of a wave if the frequency is 300. hz? E = hf f= 300. hz h = x E = 300. x x E = 1.99 x sig figs
33Example 3If the energy of a wave is x J, find frequency and wavelengthE = hfE= 9.00 x hzh = x 10-349.00x = x x ff = 1.36 x 1015 hz sig figs
34If the energy of a wave is 9 If the energy of a wave is x J, find frequency and wavelengthC = λf If f = 1.36 x 1015 hz C = 3.00 x 108 m/s 3.00 x 108 m/s = λ x 1.36 x 1015 λ = 2.21 x 10 -7m 3 sig figs.