Electron Configuration & the Quantum Mechanical Model of the Atom

Atom…a Working Model Although the Bohr model of the atom did a good job of explaining the spectrum of hydrogen, it failed with any element more complex than that. In the late 1920's the Austrian scientist Ernst Schrodinger developed the model that is still in use today. He came up with a mathematical way to predict the probability of where an electron can be found in an atom.

Quantum Mechanical Model Terminology Aufbau principle – electrons will occupy the lowest energy level possible Pauli exclusion principle – no 2 electrons will occupy the same 4 quantum numbers (n, l, m l, m s ) Hund’s rule – when there are orbitals with the same energy, each gets 1 electron (all are spinning the same way) before any orbital gets a 2 nd electron Valence electrons – outermost shell of an atom (highest energy level number) Orbitals – places where electrons like to hang out on the energy levels Introduction Video On Quantum Numbers

Identifying the 4 Quantum Numbers of an Electron 1.Principal Quantum Number (n)  represents the energy level where the electron in question is located 1s 2 2s 2

Practice Finding n What is the principal quantum number for the following electrons: a.The last electron to be placed in a chromium atom b.The 10 th electron in a barium atom

Answers a.The last electron to be placed in a chromium atom 24 Cr 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 4 n = 3 a.The 10 th electron in a barium atom 56 Ba 1s 2 2s 2 2p 6 n = 2

2.Angular Momentum Quantum Number (l)  determines the shape of the orbital 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5 s = 0 (sphere shaped) p = 1 (propeller shaped) d = 2 (double propeller shaped) f = 3 (flower shaped)

Practice Finding l What is the angular momentum quantum number for the following electrons: a.The last electron to be placed in a chromium atom b.The 10 th electron in a barium atom

Answers a.The last electron to be placed in a chromium atom 24 Cr 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 4 l = 2 a.The 10 th electron in a barium atom 56 Ba 1s 2 2s 2 2p 6 l = 1

3. Magnetic Quantum Number (m l )  Orientation of the orbital in space s = 01 orbital per s subshell p = -1, 0, 13 orbitals per p subshell d = -2, -1, 0, 1, 25 orbitals per d subshell f = -3, -2, -1, 0, 1, 2, 37 orbitals per f subshell

Practice Finding m l What is the magnetic quantum number for the following electrons: a.The last electron to be placed in a chromium atom b.The 10 th electron in a barium atom

Answers a.The last electron to be placed in a chromium atom 24 Cr 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 4 ___ ___ ___ ___ ___ m l = 1 a.The 10 th electron in a barium atom 56 Ba 1s 2 2s 2 2p 6 __ ___ ___ m l = 1

4. Spin Quantum Number (m s ) +1/2  The 1 st electron placed in an orbital has a clockwise rotation (e - points up) -1/2  The 2 nd electron placed in an orbital has a counterclockwise rotation (e - points down)

Practice Finding m s What is the spin quantum number for the following electrons: a.The last electron to be placed in a chromium atom b.The 10 th electron in a barium atom

Answers a.The last electron to be placed in a chromium atom 24 Cr 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 4 ___ ___ ___ ___ ___ m s = +1/2 a.The 10 th electron in a barium atom 56 Ba 1s 2 2s 2 2p 6 __ ___ ___ m l = -1/2

Quantum Number Review 4wlE 4wlE

Electron Configuration Hotel

3 Different Types of Notation There are 3 different ways to show the probability of where an electron can be found in an atom. 1. Orbital Notation 2. Electron Configuration 3. Noble Gas Configuration

Orbital Notation Shows the energy levels, sublevels, orbitals and electrons ( ) Most specific notation Ex. What is the orbital notation of C? S? Cu?

Answers 6 C = ___ ___ ___ ___ ___ 1s 2s 2p 16 S = ___ ___ ___ ___ ___ ___ ___ ___ ___ 1s 2s 2p 3s 3p 29 Cu = ___ ___ ___ ___ ___ ___ ___ ___ ___ 1s 2s 2p3s 3p ___ ___ ___ ___ ___ ___ 4s 3d

Electron Configuration Not as specific as orbital notation Shows the energy levels, sublevels, and number of electrons in each of the sublevels Ex. What is the electron configuration of C? S? Cu?

Answers 6 C = 1s 2 2s 2 2p 2 16 S = 1s 2 2s 2 2p 6 3s 2 3p 4 29 Cu = 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 9

Noble Gas Configuration The shortcut to electron configuration Shows the noble gas in brackets that is located one period ahead of the element you are determining configuration for for. The noble gas symbol will represent the entire electron configuration of that element. From there, you will complete the rest of the configuration needed, starting from the noble gas.

Sample Problems Ex. What is the noble gas configuration for C? S? Cu? What is the valence (outermost, highest energy level) electron configuration for each of the elements listed above?

Answers 6 C = [He]2s 2 2p 2 Valence e - configuration = 2s 2 2p 2 16 S = [Ne]3s 2 3p 4 Valence e - configuration = 3s 2 3p 4 29 Cu = [Ar]4s 2 3d 9 Valence e - configuration = 4s 2

Stability Of Noble Gases The noble gas family (group 18) consists of the most stable elements on the PT The have a full valence shell (8 e - ) with the exception of He (2 e - ) Elements will lose, gain or share electrons to gain a full valence shell ___ ___ ___ ___ s p

What Noble Gas Do Elements Want To Form? Depends on its position on the PT Elements want to look like the closest noble gas from its valence shell Predict what noble gases each of the following elements want to look like: a.O b.K c.Ga

Answers a.O  O -2 Will gain 2 e - to look like Ne from the valence shell b. K  K + Will lose 1 e - to look like Ar from the valence shell c. Ga  Ga +3 Will lose 3 e - to look like Ar from the valence shell