2 Vocabulary electron configuration aufbau principle Pauli exclusion principleHund’s ruleValence electronElectron-dot structure
3 ReviewEach principal energy level can have the same number of sublevels as the level numberEach sublevel orbital has a different shapeEach orbital can have only 2 electronsWhat does this mean?
4 Electron Arraignment follows Rules Low energy level systems are more stable than high-energy systemsAtoms will assume the electron arrangement that gives the atom the lowest energyMost stable is the “ground state” (lowest energy)Three rules/principles for arranging electronsAufbauPauli Exclusion principleHund’s Rule
5 Aufbau PrincipleEach electron occupies the lowest energy level availableLearn the sequence of atomic orbitals from lowest to highest:
6 Aufbau Diagram#4 – also do electron DOT diagram, #7 & 8 – SHOW YOUR WORK
8 Using AufbauAll orbitals related to the same energy level are of equal energyAll 2p orbitals have the same energyIn a multi-electron atom, the energy sublevels within a principal energy level have different energies:2p orbitals are higher energy than 2s orbitalsThe sequence of sublevels within a principle level in increasing energy is: s, p, d, and fOrbitals related to energy sublevels within one principle energy level can overlap orbitals related to another principal levelNotice: 4s is lower than 3d
9 Pauli Exclusion Principle Each electron has an associated spin, like a topCan spin on bottom or topEach orbital can hold AT MOST 2 electrons, but only if they have opposite spinDesignated as:
10 Hund’s RuleBecause 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?
12 Representing Atom’s Electrons Orbital DiagramsElectron Configuration Notations
13 Orbital Diagrams Draw one box for each orbital Example: Empty box means no electronsBox with single up arrow means orbital with one electronBox with two arrows (up/down) means orbital with two electronsEach box is labeled with the principle quantum number and the sublevelExample:
16 Electron Configuration Notation Specify principal energy level and energy sublevelUse a superscript to represent the number of electronsUse the Aufbau diagram to help you remember the level/sublevel filling orderExamples:
19 A Variation – Noble Gas Notation Similar to Electron Configuration Notation, but:Start with the previous noble gas, and put that symbol in bracketsAdd electrons to the noble gasExample:Sodium (Na) = [Ne] 3s1Ne = 1s2 2s2 2p6Na = 1s2 2s2 2p6 3s1
20 Exceptions to Aufbau Cr (Chromium) = [Ar] 4s1 3d5 Cu (Copper) = [Ar] 4s1 3d10
21 Valence ElectronsOnly Valence Electrons contribute to chemical bondingValence Electrons = electrons in outer most principal energy levelGenerally highest energyExamples:Carbon: [He] 2s2 2p2 has 4 valence electronsSulfur: [Ne] 3s2 3p4 has 6 valence electrons
22 Electron Dot DiagramsAlso called Lewis Electron Dot Diagrams or Lewis Electron Dot Structure or Electron Dot StructureShows atomic symbol and ONLY valence electrons