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Atomic Structure and Periodicity Chapter 7 Unit 4 - Atomic Structure, Periodicitiy, and Bonding AP Chemistry Electromagnetic Radiation Classification of Electromagnetic Radiation Wavelength decreases → Frequency decreases → Energy decreases → 8 Speed is constant = 3.00 x 10 m/s Electromagnetic Radiation Properties of Electromagnetic Waves Wavelength (λ) distance between two consecutive crests or troughs in a wave measured in meters Frequency (v) number of waves that pass a given point per second measured in hertz (1/sec) Speed (c) measured in meters per second (m/s) When one physicist asked another, “What’s new?”, the typical response is “C over lambda”. Electromagnetic Radiation Frequency and Wavelength λv = c The Nature of Matter Max Planck Quantum Theory Energy is gained or lost in whole number multiples of the quantity hv ΔE = nhv v = frequency -34 h = Planck’s constant = 6.626 x 10 Energy is transferred to matter in packets of energy called quantum. The Nature of Matter Max Planck Sample Problem A The yellow light given off by a sodium vapor lamp has a wavelength of 589 nm. a) What is the frequency of this radiation? b)Calculate the energy of one photon of yellow light. The Nature of Matter Albert Einstien Electromagnetic radiation is a stream of particles called photons. hc E = hv = λ Energy and mass are inter-related. E = mc 2 The Nature of Matter Louis de Broglie Light travels through space as a wave. Light transmits energy as particles. Particles have wavelength, exhibited by diffraction patterns. h λ= mv Large particles have very short wavelengths. All matter exhibits both particle and wave properties. The Nature of Matter Louis de Broglie Sample Problem B What is the wavelength of an electron moving with a speed of 5.87 x -28 m/s? (mass of electron = 9.11 x 10 g) 6 10 The Atomic Spectrum of Hydrogen The Atomic Spectrum of Hydrogen Continuous spectra - contains all wavelengths of light Bright line spectra Excited electrons in an atom return to lower energy states Energy is emitted in the form of a photon of definited wavelength Definite change in energy corresponds to: Definite frequency Definite wavelength hc ΔE = hv = λ Only certain energies are possible within any atom The Atomic Spectrum of Hydrogen Bright Line Spectra The Atomic Spectrum of Hydrogen Energy Transitions for Hydrogen The Bohr Model Niels Bohr The electron moves around the nucleus only in certain allowed circular orbits. Bright line spectra confirms that only certain energies exist in the atom and the atom emits photons with definite wavelengths when the electron returns to the lower energy state. The Bohr Model Shortcomings of the Bohr Model Does not work for atoms other than hydrogen Electrons do not move in circular orbits. The Quantum Mechanical Model of the Atom Quantum Mechanical Model The electron as a standing wave Do not propagate through space Fixed at both ends Only certain size orbits can contain whole numbers of half wavelengths Fits the quanta observation Orbitals are NOT circular ARE areas of probability for locating The Quantum Mechanical Model of the Atom Heisenberg Uncertainty Principle The more accurately we know the position of any particle, the less accurately we can know its momentum, and vice versa This is apparently a true story. It took place just outside of Munich, Germany. Heisenberg went for a drive and got stopped by a traffic cop. The cop asked, “Do you know how fast you were going?” Heisenberg replied, “No, but I know where I am.” Q: Why are quantum physicists so poor at sex? A: Because when they find the position, they can’t find the momenutum, and when they find the momentum, they can’t find the position. Quantum Numbers Quantum Numbers Principal Quantum Number (n) Integral Values: 1, 2, 3... Indicates probable distance from the nucleus Higher numbers = greater distance Greater distance = less tightly bound = higher energy Quantum Numbers Quantum Numbers Angular Momentum Quantum Number (l) Integral values from 0 to n-1 Indicates shapes of atomic orbitals Angular Momentum #’s and Atomic Orbitals Value of l 0 1 2 3 4 Letter used s p d f g Quantum Numbers Quantum Numbers Magnetic Quantum Number (ml) Integral values from l to -l, including zero relates to the orientation of the orbital in space relative to the other orbitals Spin Quantum Number (ms) Orbitals can only hold 2 electrons they must have opposite spins +1/2 or -1/2 Pauli Exclusion Principle - in a given atom, no two electrons can have the same set of four quantum numbers. Quantum Numbers Quantum Numbers Sample Problem C For n = 4, what are the possible values of l? For l = 2, what are the possible values of ml? Quantum Numbers Orbital Shapes and Energies Size of Orbitals defined as the surface that contains 90% of the total electron probability Orbitals of the same shape grow larger as n increases s Orbital spherical p Orbital two lobes each, dumbbell occurs in levels n = 2 and greater Quantum Numbers Orbital Shapes and Energies d Orbital clover shape occus in levels n = 3 and greater Quantum Numbers Orbital Shapes and Energies f Orbital flower shape occus in levels n = 4 and greater not involved in bonding in most compounds Quantum Numbers Orbital Shapes and Energies All orbitals with the same value of n have the same energy Lowest energy state = ground state When the atom absorbs energy, electrons may move to higher energy orbitals or an excited state. An electron sitting in a prison asked a second electron cellmate, “What are you in for?” To which the latter replied, “For attempting a forbidden transition.” Polyelectronic Atoms Polyelectronic Atoms Internal Atomic Energies Kinetic energy - moving electrons Potential energy of attraction between nucleus and electrons Potential energy of repulsion between electrons Screening or Shielding Electrons are attracted to the nucleus Electrons are repulsed by other electrons Electrons would be bound more tightly if other electrons weren’t there Electron Configuration Rules and Principles Aufbau Principle As protons are added one by one to the nucleus to build up elements, electrons are similarly added to these hydrogen-like orbitals. Hund’s Rule The lowest energy configuration for an atom is the one having the maximum number of unpaired electrons allowed by the Pauli exclusion principle. You have to be single before you can have your “Hunny” Electron Configuration Electron Configuration Aufbau Principle As protons are added one by one to the nucleus to build up elements, electrons are similarly added to these hydrogen-like orbitals. Q: What do you call a joke that is based on cobalt, radon, and yttrium? A: CoRnY Electron Configuration Electron Configuration Sample Problem D Draw the orbital diagram for the electron configuration of oxygen, atomic number 8. How many unpaired electrons does an oxygen atom possess? Electron Configuration Electron Configuration Sample Problem E Draw the orbital diagram for the electron configuration of phosphorus, atomic number 15. How many unpaired electrons does an phosphorus atom possess? Electron Configuration AP Exam Sample Sample Problem F Write the ground state electron configuration for an arsenic atom, showing the number of electrons in each subshell. a. b.Give one permissible set of four quantum numbers for each of the outermost electrons in a single As atom when it is in its ground state. c. Is an isolated arsenic atom in the ground state paramagnetic or diamagnetic? Explain briefly. d.Explain how the electron configuration of the arsenic atom in the ground state is consistent with the existence of the following known compounds: Na3As, AsCl3, and AsF5. Daily Objectives Chemistry II Honors Today, I will be able to describe the trends of elemental properties in terms of the periodic table. • LO 1.6, 1.7, 1.8, 1.9, 1.10 Which element is...? 1.Half of a dimeNickel 2.The Lone Ranger’s horse Silver 3.Not fat Tin 4.Watered down gin Hydrogen 5.A police officer Copper 6.What I do when I’m hungry Iodine 7.What torpedoed ships do Zinc 8.Male member of the Ganese tribe Manganese 9.What he did with a bucking horse Rhodium 10.What should be done with an ailing man Helium/Curium/Barium The Periodic Table Periodic Table Vocabulary Valence Electrons Outermost principle quantum level of an atom Elements in the same group (column) have the same valence electron configuration Periodic Trends Ionization Energy Ionization energy is the energy required to remove an electron from an atom. increases for successive electrons Increases across a period Electrons in the same quantum level do not shield as effectively as electrons in inner levels Irregularities at half filled and filled sublevels due to extra repulsion of electrons paired in orbitals, making them easier to remove Decreases with increasing atomic number within a group Electrons further from the nucleus are easier to remove Periodic Trends Ionization Energy Sample Problem G Referring to a periodic table, arrange the following atoms in order of increasing first ionization energy: Ne, Na, P, Ar, K Periodic Trends Ionization Energy Sample Problem H Which has the lowest first ionization energy, B, Al, C, or Si? Which has the highest? Periodic Trends Electron Affinity Electron affinity is the energy change associated with the addition of an electron. increases across a period decreases down a group Electrons farther from the nucleus experience less nuclear attraction Some irregularities due to repulsive forces in the relatively small p orbitals Periodic Trends Electron Affinity Sample Problem I The electron affinity of lithium is a negative value, where as the electron affinity of beryllium is a positive value. Use electron configuration to account for this observation. Periodic Trends Atomic Radius Atomic radius is half of the distance between radii in a covalently bonded diatomic molecule • Trends Decreases across a period increased effective nuclear charge due to decreased shielding Increases down a group addition of principle quantum levels Periodic Trends Atomic Radius Sample Problem J Referring to a periodic table, arrange the following atoms in order of increasing size: P, S, As, Se. Periodic Trends Ionic Radius Anions are larger than parent atoms. Cations are smaller than parent atoms. Ion size increases within a family Isoelectronic ions Ions with the same number of electrons Size decreases as the nuclear charge increases Periodic Trends Ionic Radius Sample Problem K +1 -1 +2 -2 Arrange the ions, K , Cl , Ca , and S , in order of decreasing size. Photoelectron Spectroscopy Photoelectron Spectroscopy Photoelectron Spectroscopy (PES) is a technique that is used to gather information about the electrons in an atom An atom is bombarded with photons. Some of the photons are absorbed and electrons are emitted. the energy is analyzed. Since we can know the energy of the photons, and we know that energy is conserved we know that the difference in energy between the photons sent into th eatom and the energy of the electrons emitted will be the potential energy of the electrons when they are attached to the atom. Remember that the potential energy of the electron in the atom is the work needed to remove the electron from the atom. Energy of emitted electron = energy of photon - work needed to remove electron from atom Photoelectron Spectroscopy Photoelectron Spectroscopy How do scientists find ionization energy? PES can tell what about an atom? PES provides evidence for ____. How does PES work? The size of a peak on a graph means ____. Electrons are held most tightly ____. Photoelectron Spectroscopy Hydrogen The whole number is the integration of the number of electrons in the spectrum. The decimal number is the work needed to remove the electron from the atom in MJ/mol. Photoelectron Spectroscopy Helium Helium has an integration of 2 and the energy is higher than hydrogen. This is because He has 2 electrons and H has 1. Also, H and He have the same level of shielding (none) while He has 2 protons and H has 1. That makes it harder to remove the electrons from He than from H. Photoelectron Spectroscopy Lithium Lithium has two sets of electrons. 1 electron has lower energy, the 2 have higher energy. On the PES spectra, a high energy number means the electron is closer to the nucleus, a low number means it is further from the nucleus. Photoelectron Spectroscopy Lithium Lithium has two sets of electrons. 1 electron has lower energy, the 2 have higher energy. Note that the peak for an electron farther from the nucleus is closer to the beginning of the graph while the peak for an electron closer to the nucleus is farther from the beginning of the graph. Think of the energy number on the graph as how hard it is to take the electron away from the atom. Photoelectron Spectroscopy Boron Boron has 2 electrons at 19.3 in the 1s. There are 2 electrons at 1.36 and 1 electron at 0.80. The 2 electrons are 2s and the 1 electron is 2p. Why are they different? They are both in the same energy level (shell), so why do they have different potential energies? Photoelectron Spectroscopy Boron The reason the 2s and 2p orbitals have different energy is that s penetrates better than p. An s orbital can overcome the effects of shielding better than p. Remember that penetration ability is: s > p > d > f Photoelectron Spectroscopy Boron So it is easier to remove an electron from the 2p orbital in B than from the 2s. That’s why the 2s are at 1.36 and the 2p is at 0.80. Photoelectron Spectroscopy Scandium Photoelectron Spectroscopy Scandium The filling order has 3d after 4s because 3d does not penetrate as well as 4s. However, in the spectrum for Sc we can see that there are 2 electrons at 0.63 and 1 at 0.77. This suggests that it is easier to remove the 4s than the 3d. This is because n=3 shieds n=4. This raises the energy of 4s once 3d starts to fill. Photoelectron Spectroscopy Photoelectron Spectroscopy Sample Problem L Identify the element shown above. Photoelectron Spectroscopy Photoelectron Spectroscopy Sample Problem M What happens to the 1s peak? What is different about the graph than the order you fill the electron orbital diagrams? Why is the 4s lower in energy than 3d? Periodic Trends AP Exam Sample Sample Problem N Account for each of the following in terms of principles of atom structure, including number, properties, and arrangements of subatomic paricles. a. The second ionization energy of sodium is about three times greater than the second ionization energy of magnesium. b.The difference between atomic radii of Na and K is relatively large compared to the difference between the atomic radii of Rb and Cs. Periodic Trends AP Exam Sample Sample Problem N Account for each of the following in terms of principles of atom structure, including number, properties, and arrangements of subatomic paricles. c. A sample of nickel chloride is attracted into a magnetic field, whereas a sample of solid zinc chloride is not. d.Phosphorus forms the fluorides PF3 and PF5, whereas nitrogen forms only NF3. Periodic Trends AP Exam Sample Sample Problem O Explain each of the following observations using principles of atomic structure and/or bonding. a. Potassium has a lower first ionization energy than lithium. b.The ionic radius of 3N is larger than that of 2O . c. A calcium atom is larger than a zinc atom. d.Boron has a lower first ionization energy than beryllium.