Chemistry 103

Lecture 7

Outline

 I. Electronic Structure (CH5)  Orbitals/Quantum Numbers  Electron Configurations EXAM I PRACTICE KEY POSTED In glass case by office (CHE118)

Classical Mechanics

 There is no limit to the number of observables we can measure simultaneously  These observables are continuous

Quantum Mechanics

 Unfortunately, extremely small particles (electrons) do not follow the laws of classical (Newtonian) physics. The new physics that mathematically treats small particles is called

Quantum Mechanics

.



Electronic Structure Quantum Mechanics

Nature of Electrons in Atoms

Energy Level Changes

•   An electron absorbs energy to “jump” to a higher energy level. When an electron falls to a lower energy level, energy is emitted. In the visible range, the emitted energy appears as a color.

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Publishing as Benjamin Cummings

Periodicity of Periodic Table

Objective: Placing Electrons about the Nucleus of an Atom for a Particular Element.

MODEL DEVELOPED (Quantum Numbers) APPLICATION (Electron Configurations)

Quantum Numbers - The Model

 Shell (n) l=0. l=1 l=2 l=3  Subshell (l)

Electron Orbitals (n & l )

 Orbital  Region of space where two electrons are likely to be found (90% probability)  Have different shapes depending on which subshell (l quantum number) they are in

Orbital Shapes

Quantum Numbers - The Model

 Shell (n) l=0. l=1 l=2 l=3  Subshell (l) Example: l=1, m l =-1,0,1  Orientation (m l )

 

How many orbitals of a given type are there?

Quantum number: m l = -l, l +1,… 0 … +l Covers the entire positive and negative range of “l” in increments of “1”.

   Example: l = 1 (p orbital type) m l = -1, 0 , 1 (there are 3 values, that label 3 different “p” orbitals - different orientations in space)

p Orbitals

• • • A

p

orbital Has a two-lobed shape Is one of three

p

orbitals that make up each

p

sublevel Increases in size as the value of

n

increases Copyright © 2005 by Pearson Education, Inc.

Publishing as Benjamin Cummings 13

Electron Orbitals

 Orbitals  There are a different number of orbitals for each subshell (l ) type:   In an s subshell (l=0), there is 1 orbital In a p subshell (l=1), there are 3 orbitals   In a d subshell (l=2), there are 5 orbitals In a f subshell (l=3), there are 7 orbitals.

Electron Spin

 The Maximum Number of Electrons any single orbital can hold is two . They are distinguished from each other by a Quantum Number called “spin”. One electron will be given the quantum number +1/2 ( ) and the other -1/2 ( ).

Learning Check

Indicate the number of electrons each will hold: A. 4

s

sublevel (n = 4, l = 0) (ANSWER=2) B. 3

d

sublevel (n = 3, l = 2) (5 orbitals of 3d) (ANSWER = 10) C.

n

= 3 (3s, 3p, 3d) (ANSWER = 18) 16

Summary of Model

 Electron Orbitals (n (shell) l (probability))  Number of orbitals (l m l (orientation))

Using the Orbital Model

ELECTRON CONFIGURATIONS & THE PERIODIC TABLE

Writing Electron Configurations

  Electron configurations tells us which energy levels the electrons for each element are located.

THREE GENERAL

rules for placing electrons about the nucleus:

Writing Electron Configurations

  Electron configurations tells us which energy levels the electrons for each element are located.

THREE

GENERAL rules for placing electrons about the nucleus:  1. Electrons fill orbitals starting with lowest energy first.

Writing Electron Configurations

  Electron configurations tells us which energy levels the electrons for each element are located.

THREE GENERAL

nucleus: rules for placing electrons about the  1. Electrons fill orbitals starting with lowest energy first  2. There can be no more than 2 electrons in any one orbital.

Aufbau Diagrams

 1s  2s 2p  3s 3p 3d    4s 4p 4d 4f 5s 5p 5d ….

6s 6p …..

 7s

Electron Configurations

Placing electrons for an atom in orbitals by order of increasing energy (lowest->highest) H He Li

Subshell Energy Order

How will you remember the energy order of the subshells? Use the periodic table!

Subshells and the Periodic Table

Practice: Electron Configurations

 S  Ge  Rb

Names of Some Representative Elements

• Several groups of representative elements are known by common names.

Copyright © 2005 by Pearson Education, Inc.

Publishing as Benjamin Cummings

Abbreviated Electron Configurations

• • An abbreviated (noble gas shorthand) configuration shows The symbol of the noble gas in brackets that represents completed sublevels The remaining electrons in order of their sublevels Example: Chlorine has a configuration of: 1s 2 2s 2 2p 6 3s 2 3p 5 [Ne] The abbreviated configuration for chlorine is: [Ne] 3s 2 3p 5 28

Practice: Electron Configurations

 S  Ge  Rb