FACT: Chemical reactions happen because electrons are shared or transferred from one substance to another MAX NUMBER OF ELECTRONS IN AN ENERGY LEVEL ENERGY LEVEL MAX # OF ELECTRONS 1 2 3 4 5 2 8 18 32 50 Write a mathematical equation that allows us to predict the Max # if we know the energy level (n) Max # = …n… ENERGY LEVEL MAX # OF ELECTRONS 1 2 3 4 5 2 8 18 32 50 Equation to calculate Max # of e 2 2n Where n is any energy level On the Back of your Max # of Elections Sheet Bohr Models Draw the Bohr Structures for elements 1-18 WHITEBOARDING Bohr Models Draw the Bohr Structure for Z=19 (Potassium) Catalyst Draw the Bohr Structure for Z=19 (Potassium) Obviously something is wrong…because the electrons fill in an unexpected order. We need a more complicated system! There are 4 Quantum #s and those #s are used to describe where an electron is likely to be found at any given time This is a lot like being able to use four “places” to describe EXACTLY where Mr. T should be at 8:00AM on Friday. The first number we already know… The Principle Quantum # (b.k.a. The NRG level) st 1 Quantum # Principle Quantum # Specifies the energy level that the electron is on But this doesn’t explain why K’s last electron goes into the th 4 energy level instead rd of the 3 nd 2 Quantum # Specifies the shape of the sub-energy level s and p Sub Energy Levels III. Quantum Mechanical Model: Atomic Orbitals E. Shapes of orbitals d orbitals ORBITAL Space occupied by a pair of electrons Four Sub-Energy Levels Sub NRG Level s Shape Sphere Max # of electrons 2 # of Orbitals 1 p Dumbbell 6 3 d 4-Lobed 10 5 f 6-8 Lobed 14 7 Sub-Energy Levels So why do electrons fill in like they do? i.e. why is K’s last electron th in the 4 NRG level? 2 Factors Influencing Electron Placement 1.Energy Level - Closer to nucleus=easy 2. Subenergy level (shape) - spdf Electron Configuration A detailed way of showing the order in which electrons fill in around the nucleus Electron Configuration Symbols - 3 5f Energy Level # of e in sub-energy level Sub-Energy Level Electron Configuration PT K Bohr Models vs. e Configs 2 2 6 1 6 2 K:1s 2s 2p 3s 3p 4s e config Write the for: 1 H: 1s 2 He: 1s 2 1 Li: 1s 2s 2 2 6 2 6 1 K: 1s 2s 2p 3s 3p 4s Again… Why are we concerned so much about electrons? So do we really need to know about all of the electrons? e configs with the NGSC represent which electons? Valence Electrons Electrons in the outermost energy level (involved in chemical reactions) Noble Gas Shortcut 2 2 6 2 6 1 1s 2s 2p 3s 3p 4s K: 1 K: [Ar] 4s So what is different? Aufbau Principle All lower energy sublevels must be full before high energy sublevels begin filling in Steps for writing NGSC 1. Write the noble gas preceding the desired element [in brackets] 2. Carry on as usual With only the first two Quantum #s, do we have as much information as possible as to where the electrons are likely to be found? rd 3 Quantum # m or magnetic Q# Specifies the orientation of an orbital in space th 4 Quantum # s or spin Q# Spin of an electron on its own axis Quantum Review st 1 Q#: Energy Level nd 2 Q#: Shape of sub rd 3 Q#: Orientation of Orbital th 4 Q#: Spin of e Quantum Review Principle (n): 1, 2, 3, 4, … Azimuthal (l): 0, 1, 2, 3 Magnetic (ml): …-2, -1, 0, 1, 2 Spin (ms): +1/2 or -1/2 Pauli Exclusion Principle No 2 electrons can have the same set of 4 quantum numbers Arrow-Orbital Diagrams A way to show orbital filling, spin, relative energy Hund’s Rule Most stable arrangement of electrons is the one with the maximum number of unpaired electrons Energy Arrow-Orbital Diagrams 3d 4s 1s 2s 2p 3s 3p Lewis Electron Dot Diagrams The easiest way to represent the # of valance electrons Steps for writing electron dot diagrams 1. Write the element’s symbol 2. Write out e config -s 3. Count # of valence e (1-8) 4. Place same # of dots as e around symbol Order to fill in an e dot 3 6 4 7 Bm 5 8 1 2 What up? Bm 1 2 Who do 1 and 2 represent? Why do 1 and 2 fill in on the same side? What up? 4 7 3 6 Bm 5 8 Who do 3-8 represent? Why do 3,4,5 and 6,7,8 fill in on different sides? What up? 4 7 3 6 Bm 5 8 1 2 Why will you never have more than eight dots? Examples of Lewis Electron Dots What is different between the dot diagrams below and the ones that we’ve been doing? Our way accounts for Quantum #s, this way doesn’t! Flame Tests Certain elements emit specific wavelengths of light when the electrons fall from outer energy levels back to their ground state. The Electromagnetic Spectrum Line Spectra of Excited Atoms • Excited atoms emit light of only certain wavelengths • The wavelengths of emitted light depend on the element. H Hg Ne