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Recap of Last Class. Recall: Werner Heisenberg formulated the Uncertanity Principle that states it is impossible for us to know an electron’s exact position (where it is) and momentum (where it is going) As a result, we cannot identify specific orbits that electrons travel in

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## Recap of Last Class

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**Recap of Last Class**• Recall: • Werner Heisenberg formulated the Uncertanity Principle that states it is impossible for us to know an electron’s exact position (where it is) and momentum (where it is going) • As a result, we cannot identify specific orbits that electrons travel in • We can only identify regions of space within an atom where an electron is most likely to be found • ORBITALS! • Schrodinger’s complex math equation allows us to: • Calculate the shape of the electron cloud • Probability of finding the electron at distinct locations within those clouds**How do the Orbitals Fill Up with Electrons?**An Introduction to Electron Configurations**Assigning an Electron’s Address Explore**• Complete the activity “Welcome to Atomos Apartments!” on page 208**Predicting Electron Locations**• We use electron configurations • The way electrons are arranged in atoms • There are rules to follow! • Aufbau principle • Electrons are added one at a time to the lowest energy orbitals available until all the electrons of the atom have been accounted for • “aufbau” • German for ‘build up or construct’**aufbau chart**1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f**Predicting Electron Locations**• Pauli’s Exclusion Principle • An orbital can hold only two electrons**Predicting Electron Locations**• Hund’s Rule • “Electrons must fill a sub-level such that each orbital has a spin up electron before they are paired with spin down electrons” • A bus analogy: • If you enter a bus and don’t know anyone on it, you will pick a seat that is completely empty rather than one that already has a person in it**Orbital Diagrams and Electron Configurations**• Electrons fill in order from lowest to highest energy • The Pauli exclusion principle holds. An orbital can hold only two electrons • Two electrons in the same orbital must have opposite signs (spins) • You must know how many electrons can be held by each orbital • 2 for s • 6 for p • 10 for d • 14 for f • Hund’s rule applies. The lowest energy configuration for an atom is the one having the maximum number of unpaired electrons for a set of orbitals • By convention, all unpaired electrons are represented as having parallel spins with the spin “up”**Electron Configuration Practice**• Just a thought… • How do you determine the number of electrons in an element? • Examples: • Oxygen • Magnesium • Argon • Scandium**Short-Hand Notation**• Use the Noble Gas symbol to abbreviate or shorten the electron configuration • Krypton • Rubidium • Zirconium**How Can We “Locate” an Electron?**Use Quantum Numbers!**Quantum Numbers**• Each electron has a specific ‘address’ in the space around a nucleus • An electrons ‘address’ is given as a set of four quantum numbers • Each quantum number provides specific information on the electrons location**Electron Configuration**state town house number street**Quantum Numbers**• state (energy level) - quantum number n • town (sub-level) - quantum number l • street (orbital) - quantum number ml • house number (electron spin) - quantum number ms**Principal Quantum Number (n)**• Same as Bohr’s n • Integral values: 1, 2, 3, …. • Indicates probable distance from the nucleus • Higher numbers = greater distance from nucleus • Greater distance = less tightly bound = higher energy**Angular Momentum Quantum Number (l)**• Integral values from 0 to n - 1 for each principal quantum number n • Indicates the shape of the atomic orbitals Table 7.1 Angular momentum quantum numbers and corresponding atomic orbital numbers**Magnetic Quantum Number (ml)**• Integral values from l to -l, including zero • Relates to the orientation of the orbital in space relative to the other orbitals • 3-D orientation of each orbital**Electron Spin Quantum Number (ms)**• An orbital can hold only two electrons, and they must have opposite spins • Spin can have two values, +1/2 and -1/2 • Pauli Exclusion Principle (Wolfgang Pauli) • "In a given atom no two electrons can have the same set of four quantum numbers"**Closer!**• Complete the Closer on Page 206**Homework**• Begin homework on page 209 – FRONT AND BACK!

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