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Teach Yourself High School Chemistry in 24 Hours

Atomic Structure and Electron Configuration

Rapid Learning Core Tutorial Series

Wayne Huang, PhDKelly Deters, MA

Russell Dahl, PhD Rapid Learning Centerwww.RapidLearningCenter.com/© Rapid Learning Inc. All rights reserved.



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Objectives

Basic structure of atomsHow to determine the number of electronsHow to place electrons in energy levels, subshellsand orbitalsHow to show electron configurations using three methodsHow to write and understand Quantum Numbers

By studying this tutorial you will learn…

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Electron Configuration Concept Map

ChemistryChemistry

MatterMatter

Studies

Previous contentPrevious content

New contentNew content

AtomsAtoms

Made of

ElectronsElectrons

Boxes and ArrowsBoxes and Arrows

Quantum NumbersQuantum Numbers

Chemical properties determined by

Location described by

SpectroscopicNotation

SpectroscopicNotation

Noble GasNotation

Noble GasNotation

3 ways to show configurations



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Atomic Structure

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Definition: Atom

Atom - n. smallest piece of matter that has the chemical properties of the element.

Often called the“Building Block of Matter”



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What’s in an Atom?An atom is made of three sub-atomic particles.

Particle Location

Nucleus

Nucleus

Outside the nucleus

Mass

1 amu = 1.67×10-27 kg

1 amu = 1.67×10-27 kg

0.00055 amu9.10×10-31 kg

Charge

+1

0

-1

Proton

Neutron

Electron

1 amu (“atomic mass unit”) = 1.66 × 10-27 kg

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The AtomNucleus

Very small relative mass

Charge = - (# of electrons)

Electron cloud

Charge = # of protons

Mass = # of protons

+ # of neutrons

Overall Charge = # of protons

- (# of electrons)

Overall Mass = # of protons

+ # of neutrons



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Protons Versus Electrons

Protons Electrons

+ Charge - Charge

Found in nucleus

# determines the “identity”of the atom

Cannot be lost or gained without changing which element it is (nuclear reaction)The ratio of protons to electrons determines the charge on the atom.

Found outside nucleus

# and configuration determine how the atom will react

Can be lost or gained—results in an atom with a charge (ion)

Contributes to mass of atom

Does not contribute significantly to mass of atom

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Electron Locations



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Definition: Electron Cloud

Electron cloud – It is the area outside of the nucleus where the electrons reside.

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Electron Clouds

Electron cloud

Principle energy levels

Subshells

Orbitals

The electron cloud is made of energy levels.

Energy levels are composed of subshells.

Subshells have orbitals.



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Definition: Subshell and Orbital

Subshell – A set of orbitals with equal energy.

Orbital – Area of probability of the electron being located.

Each orbital can hold 2 electrons.

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Types of Subshells

Subshell Begins in energy level

Number of equal energy

orbitals

Total number of electrons

possible

s

p

d

f

23

4

1

35

7

1

610

14

2

There are 4 types of subshells that electrons reside in under ordinary circumstances.

Ener

gy in

crea

ses



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Pictures of Orbitals

s orbital

3 p orbitals

5 d orbitals

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Electron Configuration



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Definition: Electron Configurations

Electron Configurations – Shows the grouping and position of electrons in an atom.

Since the number of electrons and their configuration determines the chemical properties of the atom, it is important to understand them.

Electron configurations use boxes for orbitalsand arrow for electrons.

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Aufbau Principle

Aufbau Principle: Electrons must fill subshells(and orbitals) so that the total energy of atom is at a minimum.

1

The first of 3 rules that govern electron configurations

What does this mean?

Electrons must fill the lowest available subshells and orbitalsbefore moving on to the next higher energy subshell/orbital.



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Energy and SubshellsThe energy diagram below shows the relative energy levels.

1s

2s

3s

4s

5s

2p

3p

4p

5p

3d

4d

6s

6p5d 4f

Ene

rgy

Subshells are filled from the lowest energy level to increasing energy levels.

Not that this does not always go in numerical order.

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Hund’s Rule

Hund’s Rule: Place electrons in unoccupied orbitals of the same energy level before doubling up.

2

The second of 3 rules that govern electron configurations.

How does this work?

If you need to add 3 electrons to a p subshell, add 1 to each before beginning to double up.



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Pauli Exclusion Principle

Pauli Exclusion Principle: Two electrons that occupy the same orbital must have different spins.

3

The last of 3 rules that govern electron configurations.

“Spin” describes the angular momentum of the electron

“Spin” is designated with an up or down arrow.

How does this work?

If you need to add 4 electrons to a p subshell, you’ll need to double up. When you double up, make them opposite spins.

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Br1-

-1 = 35 - electrons

Atomic number for Br = 35 = # of protons

Charge = -1

Electrons = 36

Determining the Number of Electrons

In order to properly construct an electron configuration, you must be able to determine how many electrons to use.

Charge = # of protons – # of electrons

Atomic number = # of protons

Example: How many electrons does the following have?



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Electrons = 17

0 = 17 - electrons

Atomic number for Cl = 17 = # of protons

No charge written Charge is 0Cl

Another ExampleIn order to properly construct an electron configuration, you must be able to determine how many electrons to use.

Charge = # of protons – # of electrons

Atomic number = # of protons

Example: How many electrons does the following have?

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Example: Give the electron configuration for a Cl atom

Applying the Rules

Aufbau Principle: Electrons must fill subshells (and orbitals) so that the total energy of atom is at a minimum.1

Use the 3 rules of electron configurations.

0 = 17 - electrons

No charge written Charge is 0ClAtomic number for Cl = 17 = # of protons

Electrons = 17

Place 17 electrons

Pauli Exclusion Principle: Two electrons that occupy the same orbital must have different spins.3

Hund’s Rule: Place electrons in unoccupied orbitals of the same energy level before doubling up.2

1s 2s 2p 3s 3p

4231567910111213141516178



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Spectroscopic Notation

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Definition: Spectroscopic Notation

Spectroscopic Notation – Shorthand way of showing electron configurations.

The number of electrons in a subshell are shown as a superscript after the subshelldesignation.

1s 2s 2p 3s 3p

1s2 2s2 2p6 3s2 3p5



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Writing Spectroscopic NotationDetermine the number of electrons to place.1

Fill in subshells until they reach their max (s = 2, p = 6, d = 10, f = 14).3

Follow Aufbau’s Principle for filling order.2

The total of all the superscripts is equal to the number of electrons.4

Example: Give the spectroscopic notation for S.

0 = 16 - electrons

No charge written Charge is 0SAtomic number for S = 16 = # of protons

Electrons = 16

Place 16 electrons

1s 2s 2p 3s 3p2 2 6 2 4

2 2 6 2 4+ + + + = 16

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Electron Configurations and the Periodic Table



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1s2 2s2 2p5

Configurations Within a GroupLook at the electron configurations for the Halogens (Group 7).

F

Cl

Br

I

1s2 2s2 2p6 3s2 3p5

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p5

All of the elements in Group 7 end with 5 electrons in a p subshell.

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Configurations and the Periodic Table

In fact, every Group ends with the same number of electrons in the highest energy subshell.

s1 s2

d1 d2 d3 d4 d5 d6 d7 d8 d9 d10

p1 p2 p3 p4 p5 p6

f1 f2 f3 f4 f5 f6 f7 f8 f9 f10 f11 f12 f13 f14

Each area of the periodic table is referred to by the highest energy subshell that contains electrons.

d-block

f-block

p-blocks-block



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Wondering how to remember the order of filling of the subshells? Just use the periodic table.

In order to do this, the “f” block needs to be placed in atomic order.(It’s usually written below to fit it on the paper)

Periodic Table as a Road-Map

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p subshells begin in level 2, so begin the p-block with “2p”

s subshells begin in level 1, so begin the s-block with “1s”

To see the filling order of subshells, read from left to right, top to bottom!

Periodic Table as a Road-Map

2p3p4p5p6p

3d4d5d6d

4f5f

d subshells begin in level 3, so begin the d-block with “3d”f subshells begin in level 4, so begin the f-block with “4f”

1s2s3s4s5s6s7s

1s

This tool shows that the 3d energy level is filled after the 4s energy level!



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Another Tool for Filling Order

1s

2s 2p

3s 3p 3d

4s 4p 4d 4f

5s 5p 5d 5f

6s 6p 6d

7s 7p

8s

To read the charge, move down one diagonal as far as possible, then jump to the top of the next diagonal and keep going.

There is another tool commonly used to remember orbital filling order.

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Electron Configurations ofIons



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Definition: Ion

Ion – an atom that has gained or lost electrons resulting in a net charge.

Atoms gain and lose electrons to be in a more stable state.

Usually, the “more stable state” is a full valence shell.

Outermost shell of electrons

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Look at the electron configurations for the following:

Full Valence Shell Ions

1s 2s 2p2 2 6

Br-1

O2-

Na+

Ca2+

1s 2s 2p 3s 3p2 2 6 2 6 4s 2 3d 10 4p 6

1s 2s 2p 3s 3p2 2 6 2 6

p = 35 -1 = 35 - e e = 36

p = 8 -2 = 8 - e e = 10

p = 11 +1 = 11 - e e = 10

p = 20 +2 = 20 - e e = 18

1s 2s 2p2 2 6



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Notice that O2- and Na+ have the same number and configuration of electrons.

What do you notice about each of these configurations?

Full Valence Shell Ions

1s 2s 2p2 2 6

Br-1

O2-

Na+

Ca2+

1s 2s 2p 3s 3p2 2 6 2 6 4s 2 3d 10 4p 6

1s 2s 2p 3s 3p2 2 6 2 6

They all end with full p subshells.

1s 2s 2p2 2 6 This makes them isoelectric.

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Noble Gas Configuration



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Definition: Noble Gas Notation

Noble Gas – Group 8 of the Periodic Table. They contain full valence shells.

Noble Gas Notation – Noble gas is used to represent the core (inner) electrons and only the valence shell is shown.

1s 2s 2p 3s 3p2 2 6 2 6 4s 2 3d 10 4p 5

4s 2 3d 10 4p 5[Ar]

Br

Spectroscopic

Noble gas

The “[Ar]” represents the core electrons and only the valence electrons are shown.

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How do you know which noble gas to use to symbolize the core electrons?

Which Noble Gas Do You Choose?

Think: Price is Right.

How do you win on the Price is Right?

By getting as close as possible without going over.

Choose the noble gas that’s closest without going over!

Noble Gas # of electrons

He

Ne

Ar

Kr

Xe

2

10

18

36

54



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How do you know where to start off after using a noble gas?Use the periodic table!

Where Does the Noble Gas Leave Off?

2p3p4p5p6p

3d4d5d6d

4f5f

1s2s3s4s5s6s7s

HeNeArKrXeRn

The noble gas fills the subshell that it’s at the end of.

Begin filling with the “s” subshell in the next row to show valence electrons.

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Noble Gas Notation ExampleDetermine the number of electrons to place.1

Start where the noble gas left off and write spectroscopic notation for the valence electrons.3

Determine which noble gas to use.2

Example: Give the noble gas notation for As.

0 = 33 - electrons

No charge written Charge is 0As Atomic number for As = 33 = # of protons

Electrons = 33 Place 33 electrons

[Ar] 4s 3d 4p2 10 3 18 2 10 3+ + = 33

Closest noble gas: Ar (18) Ar is full up through 3p



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Comparing the Different Notations

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Pros and Cons of Each NotationEach notation has it’s advantages and disadvantages.

Pro

Shows if electrons are paired or unpaired

Quicker than “Boxes and arrows”

Allows focus on the valence electrons (that control bonding)Quickest method

Con

Longest method

Does not show pairing of electrons

Does not show core electrons

Does not show pairing of electrons

“Boxes and arrows”

Spectroscopic notation

Noble Gas notation



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Exceptions to the Aufbau Rule

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Stability of d Subshells with 5 or 10d subshells have 5 orbitals…They can hold 10 electrons.

According to the Aufbau principle, Cr should have the following valence electron configuration:

4s2 3d4

But a half-full or completely full d subshell is more stable than the above configuration, so it is:

4s1 3d5



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Elements with ExceptionsThe following elements are excepts to the AufbauPrinciple:

Element Should be

4s2 3d4

5s2 4d4

6s2 5d4

4s2 3d9

5s2 4d9

Actually is

4s1 3d5

5s1 4d5

6s1 5d5

4s1 3d10

5s1 4d10

Cr

Mo

W

Cu

Ag

6s2 5d9 6s1 5d10Au

They are the two groups on the periodic table that begin with Cr and Cu.

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Quantum Numbers



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Definition: Quantum Numbers

Quantum Numbers – A set of 4 numbers that describes the electron’s placement in the atom.

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4 Quantum Numbers

Quantum Number

Symbol

n

l

ml

ms

Describes

Shell number

Subshelltype

Possible Numbers

Whole #s ≥ 1

Whole # < n

- l + l

+ ½ or – ½

Principal

Azimuthal

Magnetic

Spin

2, 1, -1, + ½

n

l

ml

ms

Orbital

Spin



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Determining Quantum Numbersn: principal energy level

l: subshell s = 0p = 1d = 2f = 3

ml: orbital 0s -1 0 1p -2 -1 0 1 2d

-3 -2 -1 0 1 2 3f

Give the number of the shell

coding system

Number-line system of identifying orbitals.0 is always in the middle.Number line from – l to + l

ms: spin

Coding system

↑= + ½↓ = - ½

4p 3

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Quantum Number ExamplesGive the quantum numbers for the red arrow.Example:

1s 2s 2p 3s 3p

It’s in level “3”

___, ___, ___, ___3

It’s in subshell “s”—the “code” for “s” is “0”

0

0

It’s in orbital “0”0It’s a down arrow - ½

Give the quantum numbers for the red arrow.Example:

1s 2s 2p 3s 3p

It’s in level “2”

___, ___, ___, ___2

It’s in subshell “p”—the “code” for “p” is “1”

1It’s in orbital “-1”

-1It’s an up arrow + ½

-1 0 +1



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Identifying Incorrect Quantum Numbers

Example: What’s wrong with the following sets of quantum numbers?

1, 1, 0, + ½

2, 1, -2, - ½

1, 0, 0, -1

n = 1…OK as n (energy level) can be any whole # > 0l = 1…subshell is “p”

There is no p subshell in energy level 1

n = 2…OK as n can be any whole # >0l = 1…subshell is “p”

OK as level 2 has “p”ml = -2…on the “-2” orbital

“p” subshell has 3 orbitals: ___ ___ ___-1 0 +1

No “-2” orbital in a “p” subshell. ml must be between –l and l

n = 1…OK as n can be any whole # >0l = 0…subshell is “s”

OK as level 1 has an “s”ml = 0…on the “0” orbital

OK as “s” has 1 orbital and it’s “0”ms = -1

ms must be either + ½ or – ½

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Electron configurations are written following the Aufbau principle, Hund’s Rule and the

Pauli Exclusion Principle.

Electron configurations are written following the Aufbau principle, Hund’s Rule and the

Pauli Exclusion Principle.

Electron configurations can

be shown with boxes and arrows, in spectroscopic notation, or noble

gas notation.

Electron configurations can

be shown with boxes and arrows, in spectroscopic notation, or noble

gas notation.

Atoms are made of protons, neutrons

and electrons. The configuration of the

electrons determines the chemical

properties of the atom.

Atoms are made of protons, neutrons

and electrons. The configuration of the

electrons determines the chemical

properties of the atom.

Quantum numbersdescribe the

location of an electron in an

atom and are a series of 4 numbers.

Quantum numbersdescribe the

location of an electron in an

atom and are a series of 4 numbers.

Summary

Electrons are organized in

levels, subshellsand orbitals.

Electrons are organized in

levels, subshellsand orbitals.



Congratulations

You have successfully completed the core tutorial

Atomic Structure and Electron Configuration


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Rapid Learning Center Presenting … Learning Center Presenting … Teach Yourself High School Chemistry in 24 Hours Atomic Structure and Electron Configuration Rapid Learning Core