Chemistry 103

Lecture 7

Outline

I. Electronic Structure (CH5) Orbitals/Quantum Numbers Electron Configurations

EXAM I PRACTICE KEY POSTEDIn 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.

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Periodicity of Periodic Table

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

MODEL DEVELOPED (Quantum Numbers)

APPLICATION(Electron Configurations)

Quantum Numbers - The Model Shell (n)

Subshell (l)

l=0. l=1 l=2 l=3

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)

Subshell (l)

Orientation (ml)

Example: l=1, ml=-1,0,1

l=0. l=1 l=2 l=3

How many orbitals of a given type are there? Quantum number: ml = -l, -l +1,… 0 … +l Covers the entire positive and negative range of “l” in increments

of “1”.

Example: l = 1 (p orbital type) ml = -1, 0 , 1 (there are 3 values, that label 3 different “p” orbitals - different

orientations in space)

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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

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 ( ).

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Indicate the number of electrons each will hold:

A. 4s sublevel (n = 4, l = 0) (ANSWER=2)

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

C. n = 3 (3s, 3p, 3d) (ANSWER = 18)

Learning Check

Summary of Model

Electron Orbitals (n (shell) l (probability))

Number of orbitals (l ml (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 rules for placing electrons about the

nucleus: 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

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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:

1s2 2s2 2p6 3s2 3p5

[Ne]The abbreviated configuration for chlorine is: [Ne] 3s2 3p5

Practice: Electron Configurations S

Ge

Rb