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Electron Configuration Atoms and how their electrons orbit inside them!

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Quick Note! An electron exists and moves in an orbital An orbital has a certain shape and distance from the nucleus An orbital can only hold a maximum of 2 electrons The more electrons an atom has, the more orbitals an atom has to hold all the electrons

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Quantum Numbers Quantum numbers describe the behavior of an atom’s electrons

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Quantum Numbers “n” represents the main energy level an electron occupies The bigger “n” gets, the further away from the nucleus the electron gets If more than 1 electron has the same value for “n” they are in the same “shell” “n” can only be in integer values; n≥1 The # of orbitals in a shell = n 2

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Angular Momentum Quantum Number l l represents the shape (or sublevel) of the orbital The value for l is an integer greater than or equal to 0 l = n – 1 Each number value corresponds to a shape Value for lOrbital lettershape 0sSphere 1pDumbbell 2dButterfly 3fComplex

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Magnetic Quantum Number m m represents the orientation of the orbital about the nucleus The values for m can be -l, 0, +l The amount of m values correspond to the number of orientations of that shape Value for m # orbitals of that shape Orbital lettershape 01sSphere -1, 0, 13pDumbbell -2, -1, 0, 1, 25dButterfly -3, -2, -1, 0, 1, 2, 37fComplex

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Spin Quantum Number Negative repulses negative, therefore, electrons don’t like each other Electrons want to always move in opposite directions if they have to share an orbital Spin quantum number can be + 1 / 2 or - 1 / 2

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Quantum Numbers

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Electron Configuration The arrangement of electrons in an atom Each element has a unique electron configuration An element will have the orbitals of the elements preceding it plus any additional orbitals to account for it’s extra electrons Ex: He has a level 1 s orbital, Li has both a level 1 s orbital and a level 2 s orbital

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Electron Configuration Three RULES! 1.Aufbau principle: an electron occupies the lowest- energy orbital available If we have 5 electrons, how can we fit them so the lowest energy orbitals fill first? 1s 2s 2px 2py 2pz Energy

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Electron Configuration Three RULES! 2.Pauli Exclusion Principle: no two electrons of one atom can have the same set of 4 quantum numbers If we have 4 electrons, but they only fill 2 energy levels, how can we arrange them so they are different? 1s 2s 2px 2py 2pz Energy

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Electron Configuration Three RULES! 3.Hund’s Rule: orbitals of equal energy all fill with one electron before a second electron may be added. If we have 7 electrons, how can we fill the orbitals by energy level? 1s 2s 2px 2py 2pz Energy

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Electron Configuration Hints! Find the number of electrons List all orbitals available to element Arrange orbitals from lowest to highest energy from left to right Group like orbitals together ex: put all p orbitals of one level closer together

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Orbital Notation Orbital notation is a visual notation using arrows to represent electrons and lines to represent orbitals H ___ He ___ B ___ ___ ___ ___ ___ 1s 1s 1s 2s 2p

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Electron-Configuration Notation Electron-Configuration Notations uses the principle quantum number, the orbital letter, and the number of electrons in superscript H = 1s 1 He = 1s 2 B = 1s 2 2s 2 2p 1

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Nobel Gas Notation Nobel Gas Notation is a short cut notation We know a Nobel gas will have all the orbitals up to that Nobel gas entirely filled Therefore, we can write a Nobel Gas plus any new orbitals corresponding to the new element Ca = 1s 2 2s 2 2p 6 3s 1 3p 6 4s 2 that is really long! Ca is close to Ar; Ar = 1s 2 2s 2 2p 6 3s 1 3p 6 Therefore: Ca = [Ar]4s 2

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Valence Electrons & Inner Electrons Every element has a set of valence electrons. For the s and p block, there are 8 valence electrons Electrons in the valence shell are typically in the highest occupied energy level For Argon (1s2 2s2 2p6 3s2 3p6) this is 3 For Berylium (1s2 2s2) this is 2 All non-valence electrons are inner-shell electrons If we know an electron configuration of a neutral atom, we can figure out which element it is

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