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Chemistry Chapter 5 Notes Section 5.1: Light and Quantized Energy 1) Rutherford’s model is great for showing where the protons and neutrons in an atom are, but it did not given any information about where to find the electrons or why the negative electrons did not just get stuck to the positive nucleus. 2) When elements were heated in a flame, the light they gave off was not a continuous spectrum (like with white light) but instead it was a series of lines. Each element gave off a different set of lines (called the atomic emission spectrum), and it was found to be because of the electrons in each element. This meant light could give scientists a clue of how electrons are arranged. Unfortunately, scientists are not certain about what light is like, sometimes it is like a wave, and sometimes it is like a particle. A) When light is like a wave it is called electromagnetic radiation, and is part of the electromagnetic spectrum (also includes radio waves, TV waves, microwaves, UV waves, X-rays, and gamma-rays). As a wave, there are many measurements that can be made: As a wave, there are many measurements that can be made: i) The tops of a wave are called crests. As a wave, there are many measurements that can be made: i) The tops of a wave are called crests. ii) The bottoms of a wave are called troughs. iii) The distance from the rest position (no wave) to a crest or trough is called the amplitude. iv) The length of one wave is called a wavelength and has a symbol of “λ” (lambda). Wavelength is measured in meters. Usually wavelengths are very small for electromagnetic waves v) The number of waves that pass a point in one second is called the frequency and has a symbol of “ν” (nu). Frequency is measured in Hertz (1/s) How many hertz is the first wave? How many hertz is the second wave? vi) All electromagnetic radiation travels at the same speed as light, symbolized as “c”, and is 3 x 108 in the vacuum of space vii) Speed, wavelength, and frequency are all mathematically related as: c = λ ν; this means frequency and wavelength are inversely related Label the crest, trough, amplitude, and wavelength of this wave: Label the crest, trough, amplitude, and wavelength of this wave: Crest Wavelength Amplitude Trough What is the frequency of red light which has a wavelength of 700nm ( .0000007 m)? What is the frequency of red light which has a wavelength of 700nm ( .0000007 m)? If c = λ ν, then v = c λ What is the frequency of red light which has a wavelength of 700nm ( .0000007 m)? v = c = 300000000 m/s λ .0000007 m What is the frequency of red light which has a wavelength of 700nm ( .0000007 m)? v = c = 300000000 m/s λ .0000007 m V = 4.29 x 14 10 1/s or Hz What is the wavelength of violet light which has a 14 frequency of 7.5 x 10 Hz ? What is the wavelength of violet light which has a 14 frequency of 7.5 x 10 Hz ? If c = λ ν, then λ = c v What is the wavelength of violet light which has a 14 frequency of 7.5 x 10 Hz ? λ=c v = 300000000 m/s 7.5 x 14 10 1/s What is the wavelength of violet light which has a 14 frequency of 7.5 x 10 Hz ? λ=c v = 300000000 m/s 7.5 x 14 10 1/s λ = .0000004 m or 400 nm B) When light is like a particle it is called a photon. Light is like a particle because there are only certain amounts of energy it can have, the minimum amount is called a quantum. i) Max Planck found this energy could be calculated with the formula: E = h ν; where E = energy, measured in J h = Planck’s Constant = 6.626 x 10-34 Js ν = frequency, measured in Hz or 1/s What is the energy of violet light ? What is the energy of violet light ? E=hv What is the energy of violet light ? E=hv h = 6.626 x -34 10 Js v = 7.5 x 1014 1/s (from earlier) What is the energy of violet light ? E = (6.626 x 10-34 Js)(7.5 x 1014 1/s) What is the energy of violet light ? E = (6.626 x 10-34 Js)(7.5 x 1014 1/s) E = 4.97 x -19 10 J ii) Once the minimum amount of energy is calculated, the actual energy can be a multiple of the quantum amount. (1 x E, or 2 x E, or 3 x E, etc) Section 5.2 Quantum Theory and the Atom 1) Because of the wave-particle duality of light, electrons are considered to be a particle that can behave like a wave. Mainly, it is seen that there are only certain energy levels where an electron can be found Much like going up a ladder, the electron cannot go up or down a partial energy level, and the more energy it has the higher the energy level it can be in. • A) Niels Bohr used this to explain why hydrogen (only has 1 electron) would give several lines in the emission spectrum. He said the electron could be in different rings around the nucleus just like the planets are in different orbits around the sun. This is sometimes called the planetary model of the atom B) Louis de Broglie (18921987), Werner Heisenburg (1901-1976), and Erwin Schrődinger (1887-1961) separately did experiments and calculations that showed Bohr’s model was not correct for any element other than hydrogen. Bohr’s model was replaced by the quantum mechanical model of the atom. This new model used principal quantum levels that were similar to Bohr’s orbits, but then divided the principal quantum level into sublevels. i) The principal quantum level is a number from 1-7, with 1 being the lowest energy and 7 being the highest in energy. This number often represents the period on the periodic table in which we find the element ii) The sublevels are s, p, d, and f, with s being the first sublevel and f the last (1) The s sublevel only has 1 orbital, and the orbital holds 2 electrons (2) The p sublevel has 3 orbitals, and each orbital holds 2 electrons, for a total of 6 (3) The d sublevel has 5 orbitals, and each orbital holds 2 electrons, for a total of 10 (4) The f sublevel has 7 orbitals, and each orbital holds 2 electrons, for a total of 14 iii) We put together the principal quantum number and sublevel letter to talk about a specific orbital, but not all sublevels are possible for each energy level. principal Quantum Level 1 2 3 4–7 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f Possible Sublevels s s, p s, p, d s, p, d, f 5s 5p 5d 5f 6s 6p 6d 7s 7p Section 5.3: Electron Configurations 1) Now that scientists know more specifically where the electrons are, we need to be able to show this in a simple manner so we can communicate easily with other scientists This arrangement of electrons in an atom is called an electron configuration. 2) There are three rules that we must follow when making an electron configuration: a) The aufbau principle says electrons must fill lower energy levels before electrons can fill higher energy levels. This means 1s is filled before 2s, etc B) The Pauli exclusion principle says that only two electrons can fill each orbital (remember s has 1 orbital, p has 3, d has 5, and f has 7). So s holds 2 electrons, p holds 6 electrons, d holds 10 electrons, and f hold 14 electrons. C) Hund’s rule says electrons must spread out between the orbitals (p, d, or f) before they double up. Yes No □□□ □□□ 2p 2p 3) If we use boxes to represent orbitals, then the following aufbau diagram shows all the possible places an electron could be: Notice that the energy increases from bottom to top, High Energy Low Energy and some of the orbitals do not fill in the same number order as the others. If you fill from the bottom to the top, spreading out the electrons before doubling them up, then you should be just fine. Hydrogen H □ □ □ 3p □ 3s □ □ □ 2p □ 2s □ 1s Helium He □ □ □ 3p □ 3s □ □ □ 2p □ 2s □ 1s Completely Filled Lithium Li □ □ □ 3p □ 3s □ □ □ 2p □ 2s □ 1s Beryllium Be □ □ □ 3p □ 3s □ □ □ 2p □ 2s □ 1s Boron B □ □ □ 3p □ 3s □ □ □ 2p □ 2s □ 1s Carbon C □ □ □ 3p □ 3s □ □ □ 2p □ 2s □ 1s Nitrogen N □ □ □ 3p □ 3s □ □ □ 2p □ 2s □ 1s Oxygen O □ □ □ 3p □ 3s □ □ □ 2p □ 2s □ 1s Fluorine F □ □ □ 3p □ 3s □ □ □ 2p □ 2s □ 1s Neon Ne □ □ □ 3p □ 3s □ □ □ 2p □ 2s □ 1s Completely Filled Sodium Na □ □ □ 3p □ 3s □ □ □ 2p □ 2s □ 1s Magnesium Mg □ □ □ 3p □ 3s □ □ □ 2p □ 2s □ 1s Aluminum Al □ □ □ 3p □ 3s □ □ □ 2p □ 2s □ 1s Silicon Si □ □ □ 3p □ 3s □ □ □ 2p □ 2s □ 1s Phosphorus P □ □ □ 3p □ 3s □ □ □ 2p □ 2s □ 1s Sulfur S □ □ □ 3p □ 3s □ □ □ 2p □ 2s □ 1s Chlorine Cl □ □ □ 3p □ 3s □ □ □ 2p □ 2s □ 1s Argon Ar □ □ □ 3p □ 3s □ □ 2s □ 1s Completely Filled □ □ 2p 4) The actual order of filling is: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p At this time show the orbital viewer at http://intro.chem.okstate.edu/WorkshopFolder/ Electronconfnew.html Have out color-coded periodic tables before starting. 4) The actual order of filling is: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p 5) In order to save paper, often this is condensed to just a horizontal row called an orbital diagram: 6) Arrows are used to represent the electrons, so if two arrows go in the same box, one points up and the other points down. Nitrogen N □ □ □ 2p □ 2s □ 1s Becomes: □ □ □□□ 1s 2s 2p Cobalt (27 electrons – 27 arrows) □ □ □□□ □ □□□ □ □□□□□ 1s 2s 2p 3s 3p 4s 3d Cobalt (27 electrons – 27 arrows) □ □ □□□ □ □□□ □ □□□□□ 1s 2s 2p 3s 3p 4s 3d Bromine (35 electrons) □ □ □□□ □ □□□ □ □□□□□ □□□ 1s 2s 2p 3s 3p 4s 3d 4p Oxygen (how many arrows?) □ □ □□□ □ □□□ □ □□□□□ □□□ 1s 2s 2p 3s 3p 4s 3d 4p Oxygen □ □ □□□ □ □□□ □ □□□□□ □□□ 1s 2s 2p 3s 3p 4s 3d 4p Calcium (how many arrows?) □ □ □□□ □ □□□ □ □□□□□ □□□ 1s 2s 2p 3s 3p 4s 3d 4p Calcium □ □ □□□ □ □□□ □ □□□□□ □□□ 1s 2s 2p 3s 3p 4s 3d 4p Gallium (how many arrows?) □ □ □□□ □ □□□ □ □□□□□ □□□ 1s 2s 2p 3s 3p 4s 3d 4p Gallium □ □ □□□ □ □□□ □ □□□□□ □□□ 1s 2s 2p 3s 3p 4s 3d 4p 7) Even horizontal boxes can be too much to write, so the number of electrons in each sublevel is turned into a superscript and is written out with the quantum number and the sublevel letter. This is called an electron configuration. A) If all the orbitals are filled, the entire sequence would be: 2 2 6 2 6 2 10 6 1s 2s 2p 3s 3p 4s 3d 4p 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 14 10 6 5f 6d 7p Nitrogen N □ □ □□□ 1s 2s 2p Becomes: 1s2 2s2 2p3 Cobalt □ □ □□□ □ □□□ □ □□□□□ 1s 2s 2p 3s 3p 4s Becomes: 1s2 2s2 2p6 3s2 3p6 4s2 3d7 3d Bromine (35 electrons) □ □ □□□ □ □□□ □ □□□□□ □□□ 1s 2s 2p 3s 3p 4s 3d Becomes: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5 4p What is the electron configuration for: Oxygen? What is the electron configuration for: Oxygen: 2 2 4 1s 2s 2p What is the electron configuration for: Oxygen: 2 2 4 1s 2s 2p Calcium? What is the electron configuration for: Oxygen: 2 2 4 1s 2s 2p Calcium: 2 2 6 2 6 2 1s 2s 2p 3s 3p 4s What is the electron configuration for: Oxygen: 2 2 4 1s 2s 2p Calcium: 2 2 6 2 6 2 1s 2s 2p 3s 3p 4s Gallium? What is the electron configuration for: Oxygen: 2 2 4 1s 2s 2p Calcium: 2 2 6 2 6 2 1s 2s 2p 2s 3p 4s Gallium: 2 2 6 2 6 2 10 1 1s 2s 2p 3s 3p 4s 3d 4p 8) If writing out the entire electron configuration is too much, we can use the previous (in the periodic table) noble gas to take the place of part of the electron configuration: Example: 2 2 6 2 1s 2s 2p 3s Magnesium: Neon: 1s22s22p6 Noble Gas configuration: Magnesium: [Ne] 3s2 Example: Polonium: 1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p4 Xenon: 1s22s22p63s23p64s23d104p65s24d105p6 Polonium:[Xe] 2 14 10 4 6s 4f 5d 6p 9) When the electron configuration is written for an element using the noble gas configuration the electrons written after the noble gas are the ones that appear on the outside of the atom. These electrons are called valence electrons. When elements bond to form compounds, it is these electrons that are involved. The amount of valence electrons makes a big difference in how the element will bond, so to make it easy to predict, we draw electron dot diagrams. A) In an electron dot diagram, we use the symbol of the element and dots to represent the number of valence electrons. B) Only s and p electrons with the highest quantum number count for dot diagrams, even if there are d and f electrons after the noble gas. Lithium = [He] So 1 2s Li Beryllium = [He] So Be 2 2s Boron = [He] 2 1 2s 2p So B Carbon = [He] So 2 2 2s 2p C Nitrogen = [He] So N 2 3 2s 2p Oxygen = [He] So 2 4 2s 2p O Fluorine = [He] So F 2 5 2s 2p Neon = [He] So 2 6 2s 2p or Ne [Ne]