Today is Wednesday, February 26 th , 2014 - PowerPoint PPT Presentation

today is wednesday february 26 th 2014 n.
Skip this Video
Loading SlideShow in 5 Seconds..
Today is Wednesday, February 26 th , 2014 PowerPoint Presentation
Download Presentation
Today is Wednesday, February 26 th , 2014

play fullscreen
1 / 77
Today is Wednesday, February 26 th , 2014
Download Presentation
Download Presentation

Today is Wednesday, February 26 th , 2014

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

  1. In This Lesson: Unit 2 Electrons, Orbitals, and Atomic Model History (Lesson 1 of 4) • Stuff You Need: • Periodic Table • Paper Towel Today is Wednesday,February 26th, 2014 Pre-Class: In your notebooks, draw a picture of electrons moving around the atom’s nucleus. Include arrows to show direction. You’re going to put this on a whiteboard shortly, so grab a SMALL paper towel.

  2. Today’s Agenda • A little history review… • Electron Configuration • Also known as “Where the electrons at?” • Electron Orbitals • Heisenberg Uncertainty Principle • Aufbau Principle • Pauli Exclusion Principle • Hund’s Rule • Where is this in my book? • P. 127 and following…

  3. Guiding Video • TED: George Zaidan and Charles Morton – The Uncertain Location of Electrons

  4. In the beginning… • There was Democritus, a Greek professor (460 BC - 370 BC). • He came up with the term “atom” to describe the tiny particles he suggested. • Then there was John Dalton (1803). • He studied combinations of elements in chemical reactions. • His atomic model was just a solid ball.

  5. Discovery of the Electron • In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle. • Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.

  6. Conclusions from Studying Electrons • Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons. • Atoms are neutral, so there must be positive particles in the atom to balance the negative charge of the electrons. • Electrons have so little mass that atoms must contain other particles that account for most of the mass.

  7. In shorter terms… • Electrons are important because: • They create ions. • They lead to bonding. • They determine how atoms behave.

  8. Thomson’s Atom (1897) • Called the Plum Pudding Model, as Thomson thought that electrons were like plums sitting in a positive pudding. JJ Thomson

  9. Rutherford and the Nucleus • Ernest Rutherford fired α particles (helium nuclei) at an extremely thin sheet of gold foil. • He recorded where the particles “landed” after striking (or passing through) the gold. Ernest Rutherford “Like Howitzer shells bouncing off of tissue paper.”

  10. Rutherford’s Findings • Because most particles passed through and only a very few were significantly deflected, Rutherford concluded that the nucleus: • Is small • Is dense • Is positively charged

  11. Rutherford’s Atom (1913) • After the Rutherford experiment, the atom model looked like this: • Looked like the Infinity Ward logo, but it’s wrong.

  12. Eugen Goldstein and the Proton • Eugen Goldstein is sometimes credited with the discovery of the proton. • Other times it goes to Wilhelm Wien who performed other critical measurements of the proton using an anode ray (somewhat like Thomson’s cathode ray).

  13. Jimmy Neutron and the Rutherford Atom? • Even Jimmy Neutron has an image of the Rutherford Model on his shirt! • Not so “boy genius” after all…

  14. Bohr’s Atom (1913) • Bohr thought of electrons moving around the nucleus like planets around the Sun. • His was a flat model of the atom. • In reality, the electrons actually move around the nucleus like bees around a hive. Niels Bohr

  15. The Bohr Model • Niels Bohr, among other things, proposed the Bohr Model. • Unlike Rutherford’s atom, which had electrons all at approximately the same distance from the nucleus, Bohr’s model showed them orbiting in a flat space but at different, fixed distances:

  16. Schrödinger’s Atom (1926) Louis de Broglie • In 1923, Louis de Broglie discovered that particles as small as electrons have some wave-like properties (as opposed to strictly particle-like). • More on this in our next lesson. • In 1926, Erwin Schrödinger develops equations that lead to the electron cloud model of the atom. • Electrons around found in a three-dimensional space around the nucleus and are more likely to be found closer-in. • Combined, these two discoveries do away with the Bohr model but require a more complex model of the atom. Erwin Schrödingerödinger.jpg/220px-Erwin_Schrödinger.jpg

  17. Chadwick and the Neutron • Chadwick discovered the neutron in 1932 and won the Nobel Prize three years later for it.

  18. Modern Atomic Theory • All matter is composed of atoms. • Atoms cannot be subdivided, created, or destroyed in ordinary chemical reactions. However, these changescanoccur in nuclear reactions! • Atoms of an element have a characteristic average mass which is unique to that element. • Atoms of any one element differ in properties from atoms of another element.

  19. The Quantum Mechanical Model • The currently-accepted model is the Quantum Mechanical Model of the atom. • In it, mathematical models determine the most likely positions of electrons around the nucleus. • Sound complicated? It is. • Instead of exploring the laws, we’re going to look at some of the “results” of them. • But first, an actual look at atoms on camera. • NOVA video.

  20. Heisenberg Uncertainty Principle • Werner Heisenbergdiscovered that you can find out where an electron is, but not where it’s going. • Alternatively, you can find out where it’s going but not where it is. • Not both. “One cannot simultaneously determine both the position and momentum of an electron.”

  21. Heisenberg Uncertainty Principle • To be able to see things, light must strike an object and then bounce off of it, returning to your eye. • For objects like, say, bowling balls, light strikes it and the bowling ball just sits there. • For electrons, however, they have so little mass that when light strikes them, they move in a different direction.

  22. Guiding Example • Now, before we dive face-first into electron orbitals, we’re going to use a “guiding example” from something not-so-scientific to understand the concepts behind them. • The Hog Hotel! • Remember, as we explore this analogy, the goal of this entire lesson is to learn how electrons configure themselves around the nucleus. • It’s a big game of hide and seek with electrons!

  23. The Hog Hotel Analogy • Imagine you’re the manager of a towering hotel (for pigs) and you have a list of pigs that want to stay there. • Here are the rules you need to follow: • Rooms must be filled from the ground up. • Only singles first. No pig gets a roommate until all rooms on one floor are filled. • If two pigs are staying in the same room, they will face opposite directions. Weird.

  24. The Hog Hotel Analogy • On your Hog Hotel worksheets, try the first page and #2 on the back of the first page. • Then we’ll go over it. • Then we’ll do the rest of the back page.

  25. Electron Energy Levels (Shells) • Rising up from the lobby of the hotel are the various floors hogs might occupy. • Moving away from the nucleus are the various energy levels electrons might occupy. • These energy levels are symbolized by n. • Energy Level 1 n=1 • Energy Level 2 n=2

  26. n • n is the Principal Quantum Number. • To determine how many electrons fit into a given energy level, use this formula: Electrons = 2n2 • Energy Level 1 n=1 • Energy Level 2 n=2

  27. Aufbau Principle • In German, aufbau means “building up.” • The Aufbau Principle states that electrons, when not excited, will fill energy levels starting at the lowest energy. • In the Hog Hotel, this was the rule that the hogs are lazy and prefer rooms on the lowest floors possible.

  28. Orbital Shapes • Imagine that each room in the hotel, even on the same floor, has a different shape. • In the atom, on the energy level are sublevels consisting of orbitals where there is a 90% probability of finding an electron. • An orbital is like a specific room (indicated sometimes by a direction). • Orbitals can hold up to 2 electrons. • A sublevel is like a group of rooms or a suite (indicated by a letter – also called subshells). • Sublevels can hold 1, 3, 5, or 7 orbitals.

  29. Orbital Hotel Rooms? • For the next few slides, I’m going to show you pictures of orbitals. • Think of these as rooms in a weird atomic hotel. • Some are basic rooms, holding only two electrons. • Some are like suites, with individual rooms comprising a larger room. • They don’t all appear on every floor, however.

  30. s Sublevel e- e- Orbital

  31. s Sublevels • Shape: Sphere • Appears: n=1 and above. • # of Orbitals: 1 • Capacity: 2 e-

  32. p Sublevel e- e- e- e- e- e- Orbital

  33. p Sublevels • Shape: Dumbbell (3) • Appears: n=2 and above. • # of Orbitals:3 • Capacity: 6 e-

  34. d Sublevel e- e- e- e- e- e- e- e- e- e- Orbital

  35. d Sublevels • Shape: Double Dumbbells (4) and Dumbbell Doughnut • Appears: n=3 and above. • # of Orbitals: 5 • Capacity: 10 e-

  36. f Sublevel e- e- e- e- e- e- e- e- e- e- e- e- e- e- Orbital

  37. f Sublevels • Shape: Flowers…and stuff. • Appears: n=4 and above. • # of Orbitals: 7 • Capacity: 14 e-

  38. And the “hotel” as a whole? 4s 4p 4d 4f 3s 3p 3d 2s 2p 1s

  39. Quick Review • How many electrons can fit into that s sublevel? • 2 • Which energy level is further from the nucleus, n=2 or n=5? • 5 • How many electrons can fit at the 2nd energy level? (n=2) • 8 (remember 2n2 ?) • In which energy level does the f orbital start to appear? • n=4

  40. You Should Know… • You may be feeling a little overwhelmed. • If you understand this, you’re in good shape: • Around the atom are energy levels, like floors in a hotel room. The further out, the higher energy. • Each energy level has sublevels, like “types of rooms” in a hotel. • Each sublevel has one or more orbitals, which are like individual rooms. For example, s sublevels have one orbital, whereas p sublevels have three orbitals. • These orbitals each can hold two electrons and show the 90% likely location of those two electrons at any time.

  41. Summary Table

  42. Putting It All Together • Let’s try the third and fourth pages of the hog hotel worksheet. • It’s the same thing we’ve been doing, only using “up arrows” and “down arrows” instead of forward and backward letters.

  43. Orbital Notation • What you have just learned (the arrow way of writing electrons) is called orbital notation. • As it turns out, there’s a pattern to finding the orbitals in which the last electrons are placed. • Mendeleev was on to something! • Let’s do some color-coding so we can predict the ending orbital.

  44. First shade the blocks…

  45. Inner Transition Metals • Below the table are the inner transition metals (f block). • They look disconnected, but really they are “within” the transition elements (d block). • Expanded, the table would look like this.

  46. d and f Sublevels • Uh, wait a second… • It looks like according to the table we just shaded, d and f sublevels are going out of order. • In the n=6 row, it’s 5d and 4f. • What’s the deal? • d and f sublevels exist at lower energy levels than p sublevels (starting at n=4), so they’ll be filled first. • Stick with me here – I’ll teach you an easy way to remember that.

  47. Writing Configurations • Chemists need to be able to effectively record the electron configurations of various atoms. Consider Neon, the first element on the last page of the Hog Hotel. • Neon is in the second row (n=2), so there are electrons in n=1 and n=2. • 1 2 • There are electrons in sublevels 1s, 2s, and 2p. • 1s 2s 2p • Finally, there are two electrons in sublevel 1s, two in subshell 2s, and 6 in subshell 2p. • 1s2 2s2 2p6 (electron configuration) • ↑↓↑↓↑↓↑↓↑↓(orbital notation) 1s 2s 2p

  48. Two Ways to Figure This Out… • It can be hard to remember the order of the various quantum numbers and subshells. • You can figure out the electron configuration of an element two ways. • The easy way and the hard way. • Just kidding. They’re just different. • One way is the diagonal rule. • This: • The other way is hard to explain in writing, but I like it better.

  49. Directions for Using the Cheat Sheet • Target your element. • Starting with hydrogen, move left to right across the rows, moving down one each time you reach the end. • Every time you either A) reach the end of a row or B) change blocks, write down the “address” of the last element in that section. • Stop when you get to your element. • Check your work! You should be able to count the same number of electrons (more on that in a bit).