Transcript energy
Electromagnetic Radiation and Light I. Models of the Atom • Many different models: – Dalton-billiard ball model (1803) – Thompson – plum-pudding model (1897) – Rutherford – Nuclear model of the atom (1911) – Bohr – uses quantized energy of the atom (1913) – Quantum Mechanical Model of the Atom (1926) • Each new model contributed to the model we use today. • Even our current model, does not give us an exact model of how electrons behave. A. The Bohr Model • Bohr used the simplest element, hydrogen, for his model • Proposed electron is found in specific circular paths, or orbits around the nucleus • Each electron orbit was thought to have a fixed energy level. • Lowest level-ground state • Any Higher Levelexcited state The Bohr Model cont. • One electron is capable of many different excited states (e- jumping to higher level) • Quantum: specific amount of energy an e- can gain or lose when moving energy levels • You can excite an e- with energy like electricity, the sun, or magnets Electron dropping from higher level to lower-releases energy energy B. Problems with the Bohr Model • OOPS!- Model only works with hydrogen • Did not account for the chemical behavior of atoms • WRONG: Electrons do not move around the nucleus in circular orbits • Still very helpful!! II. How do Neon Signs work? • They have “excited” gases in them. Explanation Step 1: an electron absorbs energy and moves to a higher energy level Step 2: e- drops back down to a lower energy level Step 2 Step 1 •During drop it gives off energy called a “photon” •Sometimes this energy is visible light (ROYGBIV) • When a photon is emitted, energy is released. We can calculate the energy released using the equation: E = h ν Application: Atomic Emission Spectrum • Used to determine which elements are present in a sample • Used to determine which elements are present in a star (because stars are gases) • Each element has a unique spectrum • Only certain colors are emitted because the energy released relates to specific frequency Spectroscope • A spectroscope is needed to see the atomic emission spectra, which acts similar to a prism, separating different frequencies of light Electromagnetic Spectrum • Electromagnetic spectrum is the range of all energies emitted from photons acting like waves. Electromagnetic Spectrum with Visible Light Spectrum Lab: Atomic Emission Spectra of Several Gases Light • Behaves like a particle • Behaves like a wave Characteristics of a Wave • Wavelength (lambda) – shortest distance between equivalent points on a continuous wave [Unit = meters] • Frequency (nu) – the number of waves that pass a given point per second [Unit = 1/second = s-1 = Hertz (Hz)] • Crest – Highest point of a wave • Trough – Lowest point of a wave • Amplitude (a)– height from its origin to its crest (highest point) or trough (lowest point) [Unit = meters] Amplitude Amplitude (Wavelength) (Wavelength) Wavelength and Frequency • Wavelength () and frequency () are related • As wavelength goes up, frequency goes down • As wavelength goes down, frequency goes up • This relationship is inversely proportional Wavelength and Frequency cont. c = = c / =c/ c Speed of light wavelength frequency c = 8 Speed of light (c) = 3 x 10 m/s Question Time • Calculate the wavelength () of yellow light if its frequency () is 5.10 x 1014 Hz. c Question Time • What is the frequency () of radiation with a wavelength () of 5.00 x 10-8 m? What region of the electromagnetic spectrum is this radiation? c How Much Energy Does a Wave Have? • • • • • • • Energy of a wave can be calculated E Energy Use the formula E= h E= Energy h Planck’s constant frequency = frequency h = Planck’s constant = 6.626 x 10-34 Joule . Sec Joule is a unit for energy (J) Energy and frequency are directly proportional, as frequency increases, energy increases Question Time • Remember that energy of a photon given off by an electron is E =h • How much energy does a wave have with a frequency of 2.0 x 108 Hz? ( h = 6.626 x 10-34 J.s) E = 1.3 x 10-34 Joule Visible Light, Frequency, and Energy • Red: longest wavelength (), smallest frequency () • Red: frequency smallest (), least amount of energy (E) • Violet: smallest wavelength (), largest frequency () • Violet: frequency largest (), greatest amount of energy (E) Flame Test • The flame test is a way to determine the element present in a sample • When placed in a flame, each element gives off a different color • Operates same as neon signs; electrons excited by heat and fall back down and give off different colors.