Chapter 6 Electronic Structure of Atoms

1. Chapter 6 Electronic Structure of Atoms SC 131 CHEM 1 Chemistry: The Central Science CM Lamberty

3. Quantum Mechanics: A Theory • Smallness of atoms and subatomic particles • Size of e- <10-9 of 10-9 of a gram • Speck of dust contains as many e- as there have been people on Earth since beginning • Dtm chemical and physical properties • Traditional observations not possible • e- do not move in regular patterns • e- observed behave differently than those not observed. • Quantum-mechanical model • Model to explain how e- exist in atoms and dtm properties • Explain WHY some M, some NM, why noble gases are inert, etc.

4. The Nature of Light • Wave Nature of Light • Properties of waves • The Electromagnetic Spectrum • Radio (low E) to Gamma rays (high E) • Interference and Diffraction • Ways waves may interact • The Particle Nature of Light • Photoelectric effect • photons

5. The Wave Nature of Matter • Light is electromagnetic radiation • Wave composed of oscillating mutually perpendicular electric and magnetic fields • Speed of light (vacuum) 3.00x108 m/s • Amplitude • Vertical height of crest • Determines the intensity of light

6. c n = l The Wave Nature of Matter • Wavelength • Distance between adjacent crests • Frequency • Number of cycles passing a point in given period of time • Cycles per second (s-1). 1 Hertz = 1 cycle/s • Frequency directly proportional to speed, inverse to wavelength

7. Wavelength and Amplitude

8. The Electromagnetic Spectrum • Includes ALL wavelengths of EM radiation • 10-15m (gamma) - 105m (radio waves) • Short wavelength has greater E • Gamma (g) rays • Most energetic, shortest • Produced by sun and stars and unstable atomic nuclei • Damage to biological molecules • X-rays • Longer wavelength than gamma • Pass through many substances that block visible • Can damage biological molecules

9. The Electromagnetic Spectrum • Ultraviolet • Component of sunlight for suntan/sunburn • Carries enough E to damage biological mq • excessive exposure skin cancer, cataracts • Visible • Violet (short l, high E) - red (longer l, lower E) • Violet, blue, green, yellow, orange, red • Causes certain mq in eye to change shape resulting in vision • Color we see is reflected, others absorbed • Infrared • Heat from hot object • Night vision goggles

10. The Electromagnetic Spectrum • Microwaves • Longer wavelengths • Used for radar and microwave ovens • Efficiently absorbed by water and can heat • Radio waves • Longest wavelength • Transmit signals responsible for FM and AM radio, cellular phones, TV, etc

11. Interference and Diffraction • Interference • How waves add together • Constructive or destructive • Diffraction • How waves bend to move around/though object • Diffraction of light through 2 slits • Interference pattern

12. Interference and Diffraction

13. hc E = l The Particle Nature of Light • Light initially thought of as wave • Photoelectric effect • Metals emit e- when light shines on them • Series of tests did not follow EM theory • Einstein: packets of light E = hn • h is Planck’s constant • Photons • Our name for packets of light • Sometimes called quantum of light • Light is “lumpy” • Light is shower of particles each having e of hn Wave-particle duality of light

14. Atomic Spectroscopy & Bohr Model • Study of the EM radiation absorbed and emitted by atoms • Atom absorbs E (heat, light, electricity) and remits the E as light • Each element emit light of characteristic color • Each with several distinct wavelengths • Emission spectrum • Each element has its own emission spectrum • Discrete lines not continuous

15. Atomic Spectroscopy & Bohr Model

16. Atomic Spectroscopy & Bohr Model • Johannes Rydberg • Simple equation to predict wavelength of H • 1/l = R(1/m2-1/n2) • Neils Bohr • His model: e- travel around nucleus in circular orbits. • These orbits can exist only as specific fixed distances from nucleus • E of each orbit was fixed or quantized • Stationary states • Only when e- made a transition that radiation emitted or absorbed

17. The Wave Nature of Matter • Louis de Broglie • Wave nature of electrons • Diffraction pattern • de Broglie relation l = h/mn • Heisenberg • Uncertainty Principle: cannot simultaneously observe both the wave nature and the particle nature of the electron

18. Quantum Mechanics and the Atom • Schrodinger • Orbital, probability distribution map showing where the electron is likely to be found • Wave function • Quantum Numbers used to specify each orbital or location of electron for an atom.

19. Quantum Mechanics and the Atom • Principle quantum number, n • Integer that dtm overall size and E of orbital • n= 1,2,3… • Angular quantum number, l • Integer that dtm shape of orbital • l = 0,1,2,…(n-1) • Magnetic quantum number, ml • Integer that dtm orientation of orbital • ml = -l to +l (-l, …, -1, 0, 1,…, l)

20. Quantum Mechanics and the Atom

21. Atomic Spectroscopy Explained

22. The Shapes of Atomic Orbitals • Shape important b/c covalent chemical bonds depend upon sharing of electrons and occupy these orbitals • Shapes of the overlapping orbitals dtm shape of molecule • Shape dtm primarily by l the angular momentum quantum number • l=0 s orbital • l=1 p orbital • l=2 d orbital • l=3 f orbital

23. The Shapes of Atomic Orbitals • s orbitals

24. The Shapes of Atomic Orbitals • p orbitals • 2 lobes • Node at nucleus • Orbitals are orthogonal to one another

25. The Shapes of Atomic Orbitals • d orbitals • 5 3d orbitals • 4 are cloverleaf with 4 lobes • 5th is 2-lobed with donut (see p. 266)

26. Electron Configurations • Electron configuration • Ground state • Electron spin and Pauli Exclusion Principle • Direction of arrow represents electron spin • Direction does not affect value • Direction is quantized either up or down • Spin Quantum Number, ms • +1/2 (up) or -1/2 (down)

27. Electron Configurations • Pauli Exclusion Principle • No two electrons can have the same four quantum numbers

28. Electron Configurations • Sublevel Energy Splitting in Multielectron Atoms • E(s) < E(p) < E(d) < E(f) • Sheilding • Effective nuclear charge

32. Electron Configuration of Sulfur