Atomic Bonding

1. Atomic Bonding Chapter 2

2. Matter is composed of Elements • 92 naturally occurring • Atomic Number • # of protons • Mass Number • # of protons + # of neutrons • Atomic Weight • Average • Grams/mole

4. Mole • # of atoms in 12 grams of Carbon-12 • Avogadro’s Number • 6.022*10^23 • lb mole used in English calculations • # of atoms in 12 lbm of Carbon-12 • What kind of calculations can you do using the definition of a mole?

5. Bohr Model of the Atom • Both Bohr and Schrödinger knew that matter can be thought of as either a particle or a wave • Bohr chose to think of electrons as particles with wave characteristics • This approach is usually more intuitively easy to understand

6. Practically • Most things we do in Materials Science can be handled with the Bohr model • However… • Understanding the behavior of semiconductors requires some elementary understanding of quantum mechanics • Exciting advances are being made using Nanomaterials for which the Bohr model is inadequate – we need quantum mechanics

7. For Example… • Gold has interesting properties when the particles are very small – on the nanoscale • In order to understand this behavior, you need quantum mechanics

8. Gold has been used since medieval times to create red glass Stained glass in Sulkowski castle in Bielsko-Biała , Poland European panel, 1564, with typical painted details, extensive silver stain, Cousin's rose on the face and flashed ruby glass with abraded white motif http://en.wikipedia.org/wiki/Stained_glass

9. Other Colors • Copper oxides were added to produce green, • Cobalt for blue, and • Gold was added to produce red glass.

10. Nasir ol Molk mosque, Qajar era, Shiraz. Iran http://en.wikipedia.org/wiki/Image:Nasirolmolk.jpg

11. Sainte-Chapelle in Paris: Rose window. http://en.wikipedia.org/wiki/Image:Sainte-Chapelle-Rose-window.jpg

12. Why? • Gold on the bulk scale is yellow Placer Gold - Flattened nuggets of native gold found in Lynx Creek, Arizona. Gold in quartz http://www.gc.maricopa.edu/earthsci/imagearchive/gold.htm

13. Gold Nanoparticles are red • The wavelengths of light that are absorbed change for nanoparticles • In very small particles there are so few atoms that the interactions are affected by quantum effects

15. Gold Nanoshells • When you coat a glass (SiO2) particle with gold it is called a nanoshell Computer simulation of the growth of gold nanoshell over a silica core http://www.genomenewsnetwork.org/articles/07_03/nanoshells.shtml

16. Colloidal gold on the left – Gold nanoshells tuned to absorb different wavelengths of light (6 vials on the right) http://www.nanospectra.com/physics/physics.asp

17. Naomi Halas http://www.ece.rice.edu/~halas/halas.html

18. Nova Now http://www.pbs.org/wgbh/nova/sciencenow/3209/03.html

19. Clinical Trials • Currently underway on “refractory” head and neck tumors • http://www.nanospectra.com/index.html

20. Quantum Mechanics • What the Bohr model can’t explain is that only certain energy states are possible for an electron – the very property that makes gold nanospheres so interesting • Schrödinger thought of the electron as a wave - that sometimes behaves like a particle

21. Consider a slinky

22. Only certain wavelengths are possible

23. Other wavelengths are impossible if each end is held in place

24. Electrons can be thought of as standing waves • Only certain energy levels are possible • Wave particle duality Violin strings vibrate in a standing wave

25. We model many things using mathematics • For example, the equation of a line is • y=a*x + b • a stands for the slope • b stands for the intercept

26. We model an electron as a wave, described with an equation with four parameters, the quantum numbers • n • l • ml • ms

27. Primary Quantum Number • n • Can have values from 1 to infinity, but they can only be integers • K, L, M, N • Represents the energy of the orbital, which is also related to the size of the orbital • An orbital is the region of space where you are likely to find the electron

28. Angular Momentum Quantum Number • l • Shape of the orbital • Can have values from 0 to n-1 • s, p, d, f, g, h….. • If there is more than one electron present, the angular momentum quantum number also affects the orbital energy (also called the azimuthal quantum number)

29. http://boomeria.org/chemlectures/ch9orbitals1.jpg

30. Magnetic Quantum Number • ml • Can have integer values from –l to +l • Thus, if n=1, l =0, and mlmust equal 0 • In other words, it can only have one value • If n=2, then l can equal either 0 or 1 • If it equals 1, then ml can equal –1, 0 or +1 • It can have three values

31. Remember • S orbitals correspond to l = 0 • P orbitals correspond to l = 1 • D orbitals correspond to l = 2 • F orbitals correspond to l = 3 • How many orbitals are possible for each of these types? 1 3 5 7 Corresponds roughly to the orientation of the orbital in space

32. http://www.alevelchemistry.co.uk/Module_1/HTML_Pages/Atomic_Structure/1.1_Atomic_Structure_Notes.htmhttp://www.alevelchemistry.co.uk/Module_1/HTML_Pages/Atomic_Structure/1.1_Atomic_Structure_Notes.htm

33. Spin Quantum Number • ms • +1/2 • -1/2 • Two electrons of opposite spin fill each orbital

34. The first three quantum numbers define an orbital • You need all four to define an electron

35. Shorthand Notation • Germanium has 32 protons and 32 electrons • 1s22s22p63s23p63d104s24p2

36. Electron Shells • Bonding occurs only with the electrons in the outer most shells – called the valence electrons

37. Inner electrons are called the core electrons • The valence electrons are those in the outer s and p orbitals, and any unfilled d and p orbitals.

38. 1s22s22p63s23p63d104s24p2 Germanium Valence electrons Core electrons 1s22s22p63s23p63d24s2 Titanium Chemistry happens in the valence shell

39. Electronegativity • The tendency of an atom to gain an electron • The most stable configuration of electrons is completely filled valence shells

40. - Cl Non-Metals • Elements to the right side of the periodic table • The easiest way to achieve a full valence shell is to add electrons • They have a high electronegativity Readily form anions

41. Non Metals

42. Na Metals • Elements to the left of the periodic table • The easiest way to achieve a full valence shell is to give up electrons • They have a low electronegativity Na+ Readily form cations

43. Metals

44. Elements with intemediate properties – usually considered poor metals

45. Electronegativity controls how elements combine (bond) with each other.

46. Atomic Bonding • Metallic • Ionic • Covalent

47. Metallic Bonds • Metal-Metal • Non-directional • Electrons are free to move around • Good electrical conductivity • Good thermal conductivity • What is a molecule? Metals are formed from metallic bonds

48. Metallic Bonding http://www.chm.bris.ac.uk/pt/harvey/gcse/other.html

49. Ionic Bonds • Metal-Nonmetal • Cation-anion • Non-directional • Poor electrical conductivity • Poor thermal conductivity • Ceramics are formed from ionic bonds • What is a molecule?

50. Ionic Bonding http://ibchem.com/IB/ibfiles/bonding/bon_img/NaCl4.jpg