Remainder of semester: Chapter 10, 11, 12, and then we are done! First we will start with atomic structure

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1 Announcements Weak Acid Unknown Lab write-up due tomorrow in discussion. Bring your textbook!! Electronic HW #6 Type 1 due Monday, Nov. 26 th at 7:00pm Electronic HW #6 Type 2 due Wednesday, Nov. 28 th at 7:00pm

2 Remainder of semester: Chapter 10, 11, 12, and then we are done! We want to look at why molecules have certain properties and how energy plays a role First we will start with atomic structure

3 John Dalton: 1804 First experimental support for atom Atom is small, indivisible, and has different masses This is the model we ve used so far (easy, explains gases and other laws) Does not explain a lot of things like isotopes and differing chemical properties

4 JJ Thomson: late 1800s Atom of any element can be made to emit tiny negative particles (electrons) Cathode ray tube demo Goes against what Dalton said (atoms are indivisible) plum pudding model: there are negative particles embedded in some kind of positively charged cloud

5 Ernest Rutherford: 1911 neutron experiment: shot alpha particles (positive charges) at atoms (gold foil) some alpha particles bounced back from gold foil (so there must be a concentration of mass in atom with a positive charge) Goes against plum pudding model

6 Clicker #1 How many of the following statements about atomic theory are still believed to be true? I. All atoms of the same element are identical. II. Negatively charged particles are embedded in a positively charged cloud throughout the atom. III. As verified by Rutherford, only positively charged particles called protons are found inside the nucleus. IV. J.J. Thomson provided the first experimental support for the atom. A) 0 B) 1 C) 2 D) 3 E) 4

7 Let s look at a demo Dalton couldn t explain and leads us to a good discussion about our next atomic theory DEMO: electric pickle Why does it glow? Why is it yellow/orange?

8 Example: Light Bulb Energy is related to wavelength of light, which is related to colors of light Energy travels through space through electromagnetic radiation Electromagnetic radiation contains visible light (as well as X-rays, microwaves, UV, infrared, and radiowaves)

9 Why does the pickle give off light at all and why does it have a specific color? We input energy and system transferred out energy to return to lower energy state The pickle gave the energy back by releasing it in form of visible light (for this case) Sodium in pickle gave off energy (only a certain energy at a specific wavelength which is yellow/orange)

10 What puts atoms in an excited state? When energy is applied to atoms, electrons are moving around (electrons are excited, not atoms themselves) electrons want to be near nucleus, but giving them energy forces them away from nucleus

11 How do atoms return to ground state? Release energy in order to get back closer to nucleus As electrons fall back (towards their ground state) energy is released If this energy is in right amount, it will have same wavelength as a color

12 Clicker #2 Why does the pickle (the system) give off light? Choose the best answer. A) If you run electricity through anything, it will give off light. B) When protons are in an excited state due to electricity, they glow. C) The pickle contains sodium. The electricity is causing the neutrons inside sodium to move across between the two forks and thus make it glow. D) Energy was put into the pickle (by electricity) so it s returning back to a lower energy state by releasing light.

13 DEMO: flame tests Different colors for the different ions used None of the colors are white light WHY? Energy is not a continuous spectrum, but a discrete spectrum Analogies: slide versus stairs; trombone versus piano

14 Quantized Energy Levels Energy is quantized When energy is emitted or absorbed, it comes in discrete packets electrons are excited or released towards their ground state to only certain energy levels

15 Niels Bohr: 1913 Made first attempt to show support for this idea Famous planetary model Electrons go around nucleus like an orbit

16 This model is prevalent but wrong (good at explaining energy levels though) Electrons go from one energy level to another Electrons can only exist at certain energy levels Bohr verified this mathematically and found that it worked very well for hydrogen (but it doesn t work for any other elements) Because electron to electron interaction is actually quite complex

17 DEMO: Roman Candle Different colors for each but notice that none of them emit white light Bohr could calculate energy between energy levels and accurately predict color emitted (but his model only works for hydrogen) It turns out we do not know exactly where the electron is or how it moves Bohr started us on the quantum idea though

18 Waves and Probability Our atomic models are getting more complex, less easy to visualize, and more theoretical The next step is even more so: waves and probability Sometimes an electron behaves like a particle (because it has a mass) Sometimes it behaves like a wave (like light does) This is why every electron is associated with a wavelength

19 Waves and Probability Waves are associated with probability some waves cancel each other out and are nonexistent in some places probability that you ll find an electron in a certain place Electrons are best thought of in terms of probability

20 Probability and Orbitals The firefly analogy (from textbook) You don t know exactly where the firefly is going to light up but you can predict the probability that it s going to be close to the firefly sex hormone

21 Probability and Orbitals The nucleus is where the electrons want to be Electrons travel in wavelengths We don t know how electrons get from one energy level to another but we can try to predict probability of where electrons might be This region of high probability (90%) of where you might find an electron is called an orbital

22 Clicker #3 When an electron is excited in an atom or ion A) the electron moves further from the nucleus. B) only specific quantities of energy are released in order for the electron to return to its ground state. C) white light is never observed when the electron returns to its ground state. D) the electron is only excited to certain energy levels. E) All of the above statements are true when an electron is excited.

23 Electron Configuration Electron Configuration Will post this link on website today