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Welcome to Chemistry! l Finish test (15 minutes) l Finish homework (if you finished test) l Notes on Orbital Notation and Electron Configuration l Practice Problems

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Warm Up l Draw Bohr Diagram for Carbon l What 2 types of orbitals are in carbon atom? (S,P,D,F?)

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Orbital Notation and Electron Configuration Thanks to Dr. Stephen L. Cotton and Ms. Harlan for their slides

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l Has energy levels for electrons. l Orbits are not circular. l It can only tell us the probability of finding an electron a certain distance from the nucleus. The Quantum Mechanical Model

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l The atom is found inside a blurry “electron cloud” l An area where there is a chance of finding an electron. l Think of fan blades The Quantum Mechanical Model

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Atomic Orbitals l Principal Quantum Number (n) = the energy level of the electron: 1, 2, 3, etc. l Within each energy level, the complex math of Schrodinger’s equation describes several shapes. l These are called atomic orbitals (coined by scientists in 1932) - regions where there is a high probability of finding an electron. l Sublevels- like theater seats arranged in sections: letters s, p, d, and f

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Principal Quantum Number Generally symbolized by “n”, it denotes the shell (energy level) in which the electron is located. Maximum number of electrons that can fit in an energy level is: 2n 2 How many e - in level 2? 3?

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Summary s p d f # of shapes (orbitals) Maximum electrons Starts at energy level 1 2 1 3 6 2 5 10 3 7 14 4

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One s orbital l spherical

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Three p orbitals l dumbbell-shaped

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Five d orbitals

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By Energy Level l First Energy Level l Has only s orbital l only 2 electrons l 1s 2 l Second Energy Level l Has s and p orbitals available l 2 in s, 6 in p l 2s 2 2p 6 l 8 total electrons

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By Energy Level l Third energy level l Has s, p, and d orbitals l 2 in s, 6 in p, and 10 in d l 3s 2 3p 6 3d 10 l 18 total electrons l Fourth energy level l Has s, p, d, and f orbitals l 2 in s, 6 in p, 10 in d, and 14 in f l 4s 2 4p 6 4d 10 4f 14 l 32 total electrons

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By Energy Level Any more than the fourth and not all the orbitals will fill up. l You simply run out of electrons l The orbitals do not fill up in a neat order. l The energy levels overlap l Lowest energy fill first.

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Increasing energy 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 3d 4d 5d 7p 6d 4f 5f aufbau diagram - page 133 Aufbau is German for “building up”

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Electron Configurations… l …are the way electrons are arranged in various orbitals around the nuclei of atoms. Three rules tell us how: 1) Aufbau principle - electrons enter the lowest energy first. This causes difficulties because of the overlap of orbitals of different energies – follow the diagram! 2) Pauli Exclusion Principle - at most 2 electrons per orbital - different spins

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Pauli Exclusion Principle No two electrons in an atom can have the same four quantum numbers. Wolfgang Pauli To show the different direction of spin, a pair in the same orbital is written as:

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Quantum Numbers Each electron in an atom has a unique set of 4 quantum numbers which describe it. 1) Principal quantum number 2) Angular momentum quantum number 3) Magnetic quantum number 4) Spin quantum number

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Electron Configurations 3) Hund’s Rule- When electrons occupy orbitals of equal energy, they don’t pair up until they have to. l Let’s write the electron configuration for Phosphorus We need to account for all 15 electrons in phosphorus

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l The first two electrons go into the 1s orbital Notice the opposite direction of the spins l only 13 more to go... Increasing energy 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 3d 4d 5d 7p 6d 4f 5f

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l The next electrons go into the 2s orbital l only 11 more... Increasing energy 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 3d 4d 5d 7p 6d 4f 5f

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The next electrons go into the 2p orbital only 5 more... Increasing energy 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 3d 4d 5d 7p 6d 4f 5f

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The next electrons go into the 3s orbital only 3 more... Increasing energy 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 3d 4d 5d 7p 6d 4f 5f

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Increasing energy 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 3d 4d 5d 7p 6d 4f 5f The last three electrons go into the 3p orbitals. They each go into separate shapes (Hund’s) 3 unpaired electrons = 1s 2 2s 2 2p 6 3s 2 3p 3 Orbital notation

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Orbitals fill in an order l Lowest energy to higher energy. l Adding electrons can change the energy of the orbital. Full orbitals are the absolute best situation. l However, half filled orbitals have a lower energy, and are next best Makes them more stable. Changes the filling order

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s blockd blockp blockf block

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Order for Filling Sublevels

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Write the electron configurations for these elements: lTlTitanium - 22 electrons 11s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 2 lVlVanadium - 23 electrons 11s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 3 lClChromium - 24 electrons 11s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 4 (expected) BBut this is not what happens!!

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Chromium is actually: l 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 5 l Why? l This gives us two half filled orbitals (the others are all still full) l Half full is slightly lower in energy. l The same principal applies to copper.

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Copper’s electron configuration l Copper has 29 electrons so we expect: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 9 l But the actual configuration is: l 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 10 l This change gives one more filled orbital and one that is half filled. l Remember these exceptions: d 4, d 9

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Irregular configurations of Cr and Cu Chromium steals a 4s electron to make its 3d sublevel HALF FULL Copper steals a 4s electron to FILL its 3d sublevel

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