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Electron Configurations Chapter 5 Section 3

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Vocabulary electron configuration aufbau principle Pauli exclusion principle Hund’s rule Valence electron Electron-dot structure

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Review Each principal energy level can have the same number of sublevels as the level number Each sublevel orbital has a different shape Each orbital can have only 2 electrons What does this mean?

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Electron Arraignment follows Rules Low energy level systems are more stable than high-energy systems Atoms will assume the electron arrangement that gives the atom the lowest energy Atoms will assume the electron arrangement that gives the atom the lowest energy Most stable is the “ground state” (lowest energy) Most stable is the “ground state” (lowest energy) Three rules/principles for arranging electrons Aufbau Aufbau Pauli Exclusion principle Pauli Exclusion principle Hund’s Rule Hund’s Rule

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Aufbau Principle Each electron occupies the lowest energy level available Learn the sequence of atomic orbitals from lowest to highest: Learn the sequence of atomic orbitals from lowest to highest:

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Aufbau Diagram #4 – also do electron DOT diagram, #7 & 8 – SHOW YOUR WORK

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Aufbau Expanded

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Using Aufbau All orbitals related to the same energy level are of equal energy All 2p orbitals have the same energy All 2p orbitals have the same energy In a multi-electron atom, the energy sublevels within a principal energy level have different energies: 2p orbitals are higher energy than 2s orbitals 2p orbitals are higher energy than 2s orbitals The sequence of sublevels within a principle level in increasing energy is: s, p, d, and f Orbitals related to energy sublevels within one principle energy level can overlap orbitals related to another principal level Notice: 4s is lower than 3d Notice: 4s is lower than 3d

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Pauli Exclusion Principle Each electron has an associated spin, like a top Can spin on bottom or top Can spin on bottom or top Each orbital can hold AT MOST 2 electrons, but only if they have opposite spin Designated as: Designated as:

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Hund’s Rule Because negatively charged electrons repel each other, they try to get as far away from each other as possible, therefore: Single electrons with the same spin will occupy each equal energy orbital before additional electrons with opposite spins occupy the same orbitals. WHAT?

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Hund’s Rule 1 2 3 4

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Representing Atom’s Electrons 1.Orbital Diagrams 2.Electron Configuration Notations

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Orbital Diagrams Draw one box for each orbital Empty box means no electrons Empty box means no electrons Box with single up arrow means orbital with one electron Box with single up arrow means orbital with one electron Box with two arrows (up/down) means orbital with two electrons Box with two arrows (up/down) means orbital with two electrons Each box is labeled with the principle quantum number and the sublevel Each box is labeled with the principle quantum number and the sublevelExample:

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Example Orbital Diagram - N

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Example Orbital Diagram – C & O

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Electron Configuration Notation Specify principal energy level and energy sublevel Use a superscript to represent the number of electrons Use the Aufbau diagram to help you remember the level/sublevel filling order Use the Aufbau diagram to help you remember the level/sublevel filling orderExamples:

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Electron Configuration Notation

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ElementECNElementECN Hydrogen 1s 1 Carbon 1s 2 2s 2 2p 2 Helium 1s 2 Nitrogen 1s 2 2s 2 2p 3 Lithium 1s 2 2s 1 Oxygen 1s 2 2s 2 2p 4 Beryllium 1s 2 2s 2 Fluorine 1s 2 2s 2 2p 5 Boron 1s 2 2s 2 2p 1 neon 1s 2 2s 2 2p 6

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A Variation – Noble Gas Notation Similar to Electron Configuration Notation, but: Start with the previous noble gas, and put that symbol in brackets Start with the previous noble gas, and put that symbol in brackets Add electrons to the noble gas Add electrons to the noble gasExample: Sodium (Na) = [Ne] 3s 1 Ne = 1s 2 2s 2 2p 6 Ne = 1s 2 2s 2 2p 6 Na = 1s 2 2s 2 2p 6 3s 1 Na = 1s 2 2s 2 2p 6 3s 1

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Exceptions to Aufbau Cr (Chromium) = [Ar] 4s 1 3d 5 Cu (Copper) = [Ar] 4s 1 3d 10

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Valence Electrons Only Valence Electrons contribute to chemical bonding Valence Electrons = electrons in outer most principal energy level Generally highest energy Generally highest energyExamples: Carbon: [He] 2s 2 2p 2 has 4 valence electrons Carbon: [He] 2s 2 2p 2 has 4 valence electrons Sulfur: [Ne] 3s 2 3p 4 has 6 valence electrons Sulfur: [Ne] 3s 2 3p 4 has 6 valence electrons

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Electron Dot Diagrams Also called Lewis Electron Dot Diagrams or Lewis Electron Dot Structure or Electron Dot Structure Shows atomic symbol and ONLY valence electrons

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Electron Dot Diagrams

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Periodic Table

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