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Objectives SWBAT distinguish among the Aufbau principle, the Pauli exclusion principle, and Hund’s rule. SWBAT write electron configurations for selected elements.

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Electron Configuration for Neutral Atoms

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Electron Cloud A region surrounding the nucleus with the highest probability of finding electrons Electron Cloud Nucleus

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Principal Quantum Number: (main energy level) Certain regions within the electron cloud where electrons are found. Main energy levels range from 1 to 7 based on the distance from the nucleus. The higher the number, the further from the nucleus. 1 2 3 4 5 6 7

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Sublevels in main energy levels Describes the shape of the orbital that an electron occupies Labeled s,p,d,f according to shape As you move further from the nucleus (higher energy level), more electrons can be in an energy level…so the # of sublevels increases

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Orbital Shape 3D region around the nucleus There are different orbitals for the orientations around the nucleus Each orbital can hold 2 electrons – but they must have opposite spins

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s orbital - sphere

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p orbital – peanut/propeller

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d orbital – desk fan f orbital – flower

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Principal quantum number: main en level (n) Sublevels In main en. level (n sublevels) # of orbitals per sublevel # of electrons per sublevel # of e- per main en level (2n 2 ) 1s122 2spsp 1313 2626 8 3spdspd 135135 2 6 10 18 4spdfspdf 1 3 5 7 2 6 10 14 32

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Review… Where are electrons located in an atom? In the electron cloud – a region surrounding the nucleus with the highest probability of finding electrons –Where are electrons within the electron cloud? –In certain regions called Energy Levels (n=1,2,3,4,5,6,7), based on the distance from the nucleus Where are electrons within an Energy Level? In Sublevels, which have specific shapes (ex. s, p, d, f) –Where are electrons within a Sublevel? –In orbitals! But only 2 electrons per orbital.

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Electron Configuration Tells us where electrons are in an atom for a neutral atom –Shows what energy level, sublevel, and orbital

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Electron Configuration Numbers and letters used to represent orbitals with the raised number showing electrons H: 1s 1 1 st energy level, s sublevel, 1 e - Energy Levelsublevel # of electrons

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3 Rules for Electron Arrangement Aufbau Principle –Electrons always start filling at the lowest energy level. –Within each energy level, the s sublevel fills first, then p, then d, then f.

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3 Rules for Electron Arrangement Pauli Exclusion Principle –A maximum of 2 electrons can be in one orbital. They must have opposite spins.

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3 Rules for Electron Arrangement Hund’s Rule –Electrons fill each orbital in a sublevel before they start pairing up. p orbitals

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3 Ways to Represent Electron Configurations 1.Orbital Notation (diagram) 2.Electron-configuration Notation 3.Noble Gas Notation

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Orbital Diagram 1s 2s 2p x 2p y 2p z Neutral atom of Oxygen 8 protons = 8 electrons

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Electron Configuration Notation The electron configuration for oxygen. Eliminate lines and arrows of orbital diagram 1s 2 2s 2 2p 4

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4s is filled before 3d because the 4s sublevel has a lower energy then the 3d sublevel

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Drill: pd 310/29/14 Write the electron configurations for the following elements: P, Ar, and Br.

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P151s 2 2s 2 2p 6 3s 2 3p 3 [Ne]3s 2 3p 3 Element# of e- e- configuration Nobel gas notation Ar181s 2 2s 2 2p 6 3s 2 3p 6 Ca201s 2 2s 2 2p 6 3s 2 3p 6 4s 2 [Ar]4s 2 Ne101s 2 2s 2 2p 6 [He]2s 2 2p 6 or [Ne] Br35 [Ne]3s 2 3p 6 [Ar]4s 2 3d 10 4p 5 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 5

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Objectives SWBAT distinguish among the Aufbau principle, the Pauli exclusion principle, and Hund’s rule. SWBAT write electron configurations for selected elements.

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Noble Gas Notation Shorthand e - configuration –e - configurations of noble gases can be written using bracketed symbols ex: Ne 1s 2 2s 2 2p 6 = [Ne] –Write the bracketed symbol for the noble gas that precedes the element (period above it) and then continue filling orbitals with remaining electrons.

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Drill 10/30, 31/14 What are the rows on the periodic table called? What about the columns?

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Periodic Table The rows on the periodic table are called periods. How many periods are there? 7 The columns on the periodic table are called families or groups. How many groups are there? 18

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Valence electrons Valence electrons = # of e- in outermost orbital (highest main en level). These are the electrons that determine chemical properties of each element

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Take out your periodic table We are going to look at the relationship between how the periodic table is organized and electron configuration.

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S, p,d, and f-block elements The odd shape of the periodic table becomes clear if we divide it into sections based on an atom’s energy sublevel being filled with valence electrons. Sublevels = spdf!

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Mark these sublevels on your periodic table.

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What is the relationship between the maximum number of electrons an energy sublevel can hold and the size of that block?

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The number of columns in the block is equal to the maximum number of electrons the energy sublevel can hold. s = 2p = 6 d = 10 f = 14

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Valence Electrons – across periods For s and p sublevels only! Across – increase Na Mg Al Si … Ar 3s 1 3s 2 3s 2 3p 1 3s 2 3p 2 …3s 2 3p 6 1 2 3 4... 8

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Valence Electrons and groups For s and p sublevels only! This is one of the most important relationships in chem. Atoms in the same group have similar chemical properties because they have the same number of valence electrons.Down the column – stays the same. This is one of the most important relationships in chem. Atoms in the same group have similar chemical properties because they have the same number of valence electrons. Be Mg Ca Sr 2s 2 3s 2 4s 2 5s 2 2 2 2 2

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Valence electrons & Period The main energy level of an element’s valence electrons indicates the period on the periodic table in which it is found. For. Ex. Li – valence electron is in the second main energy level and is found in period 2.

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Quantum Numbers Activity

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Quantum Numbers Quantum numbers specify the properties of the atomic orbitals, and the properties of electrons in orbitals. Based on Schrodinger’s equation. If electron configuration is an e-’s address, quantum numbers would be its latitude and longitude.

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Principal Quantum Number Angular Momentum Quantum Number Magnetic Quantum Number Spin Quantum Number Take out of piece of paper. Fold it twice to form sections for the headers below. Write the headers in each section.

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Record for each Quantum # Definition Symbol The allowed values An example You will need a textbook to look up information about the quantum numbers. Pg. 101.

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Quantum Number Review Notes

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Quantum Numbers Used to describe various properties of the orbitals Each electron is assigned a set of four quantum numbers which, in order, are n, l, m l, and m s It’s like giving each electron its own latitude and longitude

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Principle quantum number Definition: indicates the main energy level occupied by the electron Symbol: n Values: (written as integers) 1,2,3,4,5,6,7

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Angular Momentum Quantum Numbers Definition: indicates the shape of the orbital Symbol: l Values: –0 = s –1 = p –2 = d –3 = f For a specific energy level, the number of orbital shapes (sublevels) available is equal to n. The values of l are equal to n-1.

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Magnetic Quantum Numbers Definition: represents the orientation of an orbital around the nucleus Symbol: m l Values: for a p-orbital -1, 0, 1 The number of different possible values for m l determine the number of orbitals in a sublevel.

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Spin Quantum Numbers Definition: represents the spin states of electrons in an orbital Symbol: m s Values: +1/2, - ½

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Mark these on your periodic table.

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Can an e- be described by the following set of quantum numbers? n=2, l=1, m l = -1 All quantum numbers are allowed values

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Can an e- be described by the following set of quantum numbers? n=1, l=1, m l = +1 Not possible. The value of l must be less than the value of n.

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Can an e- be described by the following set of quantum numbers? n=7, l=3, m l = +3 All the quantum numbers are allowed values.

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Can an e- be described by the following set of quantum numbers? n=3, l=1, m l =-3 Not possible. The value of m l must be in the range -l to +l

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Writing Quantum Numbers You can identify the quantum numbers for any electron in an element Start by writing out the the electron configuration and orbital diagram for the element Locate the electron in the orbital diagram that you are solving the quantum number for Determine the 4 quantum numbers

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Hydrogen’s electron Write electron configuration Draw orbital diagram n= 1 l= 0 m l = 0 m s = +1/2

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Helium’s second electron Write electron configuration Draw orbital diagram n= 1 l= 0 m l = 0 m s = -1/2

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Lithium’s third electron Write electron configuration Draw orbital diagram n= 2 l= 0 m l = 0 m s = +1/2

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Oxygen’s fourth electron Write electron configuration Draw orbital diagram n= 2 l= 0 m l = 0 m s = -1/2

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Flourine’s 6 th electron Write electron configuration Draw orbital diagram n= 2 l= 1 m l = 0 m s = +1/2

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