2 Electromagnetic Spectrum Visible spectrumHIGHENERGYVioletBlueGreenYellowOrangeRedLOWENERGY400 nm500 nm600 nm700 nmWhiteLightg raysX-raysUltravioletInfraredMicrowaveRadio wavesRadarTVFMShortWaveLongWaveWater waves transmit energy through space by the periodic oscillation of matter.• Energy that is transmitted, or radiated, through space in the form of periodic oscillations of an electric and a magnetic field is called electromagnetic radiation.Electromagnetic radiation– Consists of two perpendicular waves, one electric and one magnetic, propagates at the speed of light, abbreviated c, and has a value of x 108 m/s– Is radiant energy that includes radio waves, microwaves, visible light, X -rays, and gamma rays– Various kinds of electromagnetic radiation all have the same speed (c) but differ in wavelength and frequency– Frequency of electromagnetic radiation is inversely proportional to the wavelengthc = or = c/– Energy of electromagnetic radiation is directly proportional to its frequency (E ) and inversely proportional to its wavelength (E 1/)10-2nm10-1nm100nm101nm102nm103nm10-3cm10-2cm10-1cm100cm101cm1cm101m102m103m104mWavelength, l1019Hz1018Hz1017Hz1016Hz1015Hz1014Hz1013Hz1012Hz1011Hz1010Hz109Hz100 MHz10 MHz1 MHz100 KHzFrequency, nElectromagnetic spectrumDavis, Frey, Sarquis, Sarquis, Modern Chemistry 2006, page 98
3 Photoelectric Effect Light is a form of energy Light can hit a metal surface and cause the metal to emit electronsThe photoelectric effectLight travels in wavesLight at any frequency can hit a metal surface and cause the metal to emit electrons
5 Photoelectric EffectLightNucleusMetalA metal did not emit electrons when certain frequencies of light hit it When red light strikes a metal surface, no electrons are ejected.
6 Photoelectric EffectLightElectronNucleusMetalThere was a minimum frequency of light needed to get a metal to emit electrons When green light strikes a metal surface, electrons are ejected.
7 Planck’s ExplanationIf electromagnetic radiation acted as a wave, then it would emit energy continuouslyInstead, electromagnetic radiation is emitted in small specific amountsCalled quantaAKA: Things come in chunksQuantum: the minimum energy that can be lost or gained by an atom
8 Continuous vs. Quantized A BZumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 330
9 Einstein’s Explanation Built off of Planck’s ideasAgreed that electromagnetic radiation would emit energy continuously if it acted as a waveAgreed that electromagnetic radiation emits quanta
10 Einstein’s Explanation Noticed that electromagnetic radiation is sometimes continuous and sometimes quantizedProposed a dual wave-particle nature of electromagnetic radiationLight has wavelike propertiesLight can be thought of as a stream of particles
11 Einstein’s Explanation Defined the term photonA particle of electromagnetic radiation (light) that has no mass and carries a quantum (bundle) of energyIn order for the photoelectric effect to occurThe metal is struck by photonsEach photon must carry a certain amount of energy in order to knock an electron loose from the metal
12 5.1The Bohr ModelBohr proposed that an electron is found only in specific circular paths, or orbits, around the nucleus.
13 Bohr Model of Hydrogen Nucleus Possible electron orbits e e Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 331
14 5.1The Bohr ModelEach possible electron orbit in Bohr’s model has a fixed energy.The fixed energies an electron can have are called energy levels.A quantum of energy is the amount of energy required to move an electron from one energy level to another energy level.
15 5.1The Bohr ModelLike the rungs of the strange ladder, the energy levels in an atom are not equally spaced.The higher the energy level occupied by an electron, the less energy it takes to move from that energy level to the next higher energy level.These ladder steps are somewhat like energy levels. In an ordinary ladder, the rungs are equally spaced. The energy levels in atoms are unequally spaced, like the rungs in this ladder. The higher energy levels are closer together.
16 The Quantum Mechanical Model 5.1The Quantum Mechanical ModelThe propeller blade has the same probability of being anywhere in the blurry region, but you cannot tell its location at any instant. The electron cloud of an atom can be compared to a spinning airplane propeller.The electron cloud of an atom is compared here to photographs of a spinning airplane propeller. a) The airplane propeller is somewhere in the blurry region it produces in this picture, but the picture does not tell you its exact position at any instant. b) Similarly, the electron cloud of an atom represents the locations where an electron is likely to be found.
17 The Quantum Mechanical Model 5.1The Quantum Mechanical ModelIn the quantum mechanical model, the probability of finding an electron within a certain volume of space surrounding the nucleus can be represented as a fuzzy cloud. The cloud is more dense where the probability of finding the electron is high.The electron cloud of an atom is compared here to photographs of a spinning airplane propeller. a) The airplane propeller is somewhere in the blurry region it produces in this picture, but the picture does not tell you its exact position at any instant. b) Similarly, the electron cloud of an atom represents the locations where an electron is likely to be found.
18 5.1Atomic OrbitalsAn atomic orbital is often thought of as a region of space in which there is a high probability of finding an electron.Each energy sublevel corresponds to an orbital of a different shape, which describes where the electron is likely to be found.
19 5.1Atomic OrbitalsDifferent atomic orbitals are denoted by letters. The s orbitals are spherical, and p orbitals are dumbbell-shaped.The electron clouds for the s orbital and the p orbitals are shown here.
20 5.1Atomic OrbitalsFour of the five d orbitals have the same shape but different orientations in space.The d orbitals are illustrated here. Four of the five d orbitals have the same shape but different orientations in space. Interpreting Diagrams How are the orientations of the dxy and dx2 – y2 orbitals similar? How are they different?
21 VocabularyOrbitalThe space around a nucleus that has a high probability of finding an electronSimply a probability graph of where we can find an electronQuantum numbers: tell us the properties of atomic orbitals and the properties of electrons in the orbitalsPrinciple quantum numberSymbol: nThe energy level that an electron occupiesAngular momentum quantum numberSymbol: lThe shape of the orbitalSpin quantum number+1/2 or -1/2Spin state of an electron