MODELS OF THE ATOMBeginning with Rutherford

Section 7.5

The Quantum Mechanical Model of the Atom

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PROBLEMS WITH RUTHERFORD’S MODEL

It didn’t explain WHY metals and metal compounds give off characteristic colors when they are flame tested

It didn’t explain why metals glow when heated – first red, orange yellow and then white

It didn’t explain the CHEMICAL properties of elements

Section 7.5

The Quantum Mechanical Model of the Atom

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BOHR’S THEORY Electrons are located

at specific energy levels surrounding the nucleus

Each rung on the ladder represents an energy level

The higher the energy level – the farther it is from the nucleus

Bohr thought the electrons moved in fixed

ORBITS around the nucleus – we know

this is not true today

Section 7.5

The Quantum Mechanical Model of the Atom

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BOHR MODEL First model of the electron structure Gives levels where an electron is most likely to be

found Incorrect today, but a key in understanding the

atom

4

Section 7.4

The Bohr Model

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5

• Bohr’s model gave hydrogen atom energy levels consistent with the hydrogen emission spectrum.

• Ground state – lowest possible energy state (n = 1)• Bohr’s model is incorrect. This model only works for

hydrogen.• Electrons do not move around the nucleus in

circular orbits.

Electronic Transitions

in the Bohr Model for

the Hydrogen Atom

a) An Energy-Level

Diagram for Electronic

Transitions

Electronic Transitions in

the Bohr Model for the

Hydrogen Atom

b) An Orbit-Transition

Diagram, Which

Accounts for the

Experimental Spectrum

Section 7.5

The Quantum Mechanical Model of the Atom

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SCHRÖDINGER'S THEORY

He agreed that electrons have a specific amount of energy

He believed that the distance between rungs on the ladder were not consistent – they get closer together as you move higher up

Quantum – the amount of energy needed to move from one energy level to another

The electrons move

in regions of

probability around

the nucleus called

ORBITALS

Section 7.5

The Quantum Mechanical Model of the Atom

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Quantum theory, also called wave mechanics, describes the arrangement and space occupied by electrons. Orbitals refers to the three-dimensional regions in space where there is a high probability of finding an electron around an atom.

7

Section 7.5

The Quantum Mechanical Model of the Atom

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CHARACTERISTICS OF ELECTRONSExtremely small massLocated outside the nucleusMoving at extremely high

speeds in a sphereHave specific energy levels

8

Section 7.5

The Quantum Mechanical Model of the Atom

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ENERGY OF ELECTRONSWhen atoms are heated, bright lines

appear called line spectraElectrons in atoms arranged in

discrete levels. An electron absorbs energy to “jump”

to a higher energy level. When an electron falls to a lower

energy level, energy is emitted. 9

Section 7.5

The Quantum Mechanical Model of the Atom

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LOSS AND GAIN OF ENERGY

10

G

a

I

n

L

o

s

s

Section 7.5

The Quantum Mechanical Model of the Atom

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LEARNING CHECKAnswer with1) Energy absorbed 2) Energy emitted3) No change in energyA. What energy change takes place when an electron in a hydrogen atom moves from the first (n=1) to the second shell (n=2)?B. What energy change takes place when the electron moves from the third shell to the second shell?

11

Section 7.5

The Quantum Mechanical Model of the Atom

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SOLUTIONA. 1) Energy absorbed

B. 2) Energy emitted

12

Section 7.5

The Quantum Mechanical Model of the Atom

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RELATIVE ORBITAL SIZE Difficult to define precisely. Orbital is a wave function. Picture an orbital as a three-dimensional

electron density map. Hydrogen 1s orbital:

Radius of the sphere that encloses 90% of the total electron probability.

13

• We do not know the detailed pathway of an electron.

• The electrons move in regions of probability around the

nucleus called ORBITALS

Section 7.5

The Quantum Mechanical Model of the Atom

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THE ELECTRONS MOVE IN REGIONS OF PROBABILITY AROUND THE NUCLEUS CALLED ORBITALS

DEFINING THESE ORBITALS:Quantum Numbers are used to define: The energy of the electron The electron’s relative distance from the nucleus The size and shape of the ORBITAL The pairings of the electrons

Section 7.5

The Quantum Mechanical Model of the Atom

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QUANTUM NUMBERSPrinciple Quantum Number (n) – define

the energy of the electron

n=1 is closest to the nucleus – low energy

n=2 is farther than n=1, slightly more energy

n=3 is farther than n=1 and n=2, still increasing in energy

n=4 …..Remember – The difference in energy

between energy levels decreases as “n” increases

Section 7.5

The Quantum Mechanical Model of the Atom

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SUBLEVELSWithin each principle energy level (n) – there

are sublevel(s). The larger the value of ‘n’, the more sublevels

you can have.Sublevels – named by their shape

s – sphere p – pear d- dumbbell f - fundamental

Section 7.5

The Quantum Mechanical Model of the Atom

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TWO REPRESENTATIONS FOR AN S ORBITAL

Figure 3.16, pg. 77

Investigating Chemistry, 2nd Edition

© 2009 W.H. Freeman & Company

Section 7.5

The Quantum Mechanical Model of the Atom

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REPRESENTATIONS FOR P ORBITALSEACH ORBITAL CAN HOLD UP TO 2 ELECTRONS, REGARDLESS OF SHAPE. THIS SET OF THREE ORBITALS HOLDS 6 ELECTRONS.

Figure 3.17, pg. 77

Investigating Chemistry, 2nd Edition

© 2009 W.H. Freeman & Company

Section 7.5

The Quantum Mechanical Model of the Atom

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THERE IS A SET OF FIVE DIFFERENT D ORBITALS.THERE IS A SET OF SEVEN F ORBITALS.EACH ORBITAL REGARDLESS OF ITS SHAPE HOLDS 2 ELECTRONS.

Section 7.7

Orbital Shapes and Energies

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20

1s Orbital

Section 7.7

Orbital Shapes and Energies

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21

Two Representations of the Hydrogen 1s, 2s, and 3s Orbitals

Section 7.7

Orbital Shapes and Energies

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22

2px Orbital

Section 7.7

Orbital Shapes and Energies

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23

2py Orbital

Section 7.7

Orbital Shapes and Energies

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24

2pz Orbital

Section 7.7

Orbital Shapes and Energies

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25

The Boundary Surface Representations of All Three 2p Orbitals

Section 7.7

Orbital Shapes and Energies

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26

3dx2-y2 Orbital

Section 7.7

Orbital Shapes and Energies

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27

3dxy Orbital

Section 7.7

Orbital Shapes and Energies

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28

3dxz Orbital

Section 7.7

Orbital Shapes and Energies

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29

3dyz Orbital

Section 7.7

Orbital Shapes and Energies

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30

Orbital 23zd

Section 7.7

Orbital Shapes and Energies

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31

The Boundary Surfaces of All of the 3d Orbitals

Section 7.7

Orbital Shapes and Energies

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32

Representation of the 4f Orbitals in Terms of Their Boundary Surfaces

Section 7.5

The Quantum Mechanical Model of the Atom

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SUBLEVELS

Principle Energy Level Sublevel n= 1 s

n=2 s and p

n=3 s and p and d

n=4 s, p, d, and fNOTICE: The value of ‘n’ tells you how many

sublevels are present in that energy level

Section 7.6

Quantum Numbers

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34

• Principal quantum number (n) – size and energy of the orbital.

• Angular momentum quantum number (l) – shape of atomic orbitals (sometimes called a subshell).

• Magnetic quantum number (ml) – orientation of the orbital in space relative to the other orbitals in the atom.

QUANTUM NUMBERS FOR THE FIRST FOUR LEVELS OF ORBITALS IN THE HYDROGEN ATOM

35

Section 7.6

Quantum Numbers

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36

Exercise

For principal quantum level n = 3, determine the number of allowed subshells (different values of l), and give the designation of each. (hint refer to previous chart)

# of allowed subshells = 3

l = 0, 3s

l = 1, 3p

l = 2, 3d

Section 7.6

Quantum Numbers

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37

Exercise

For l = 2, determine the magnetic quantum numbers (ml) and the number of orbitals. (note refer to previous chart)

magnetic quantum numbers = –2, – 1, 0, 1, 2

number of orbitals = 5

Section 7.7

Orbital Shapes and Energies

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Locating these on the Periodic Table

Principle Energy Level (n) – is the period in the periodic table

The Sublevels are located in specific regions – Color these together

Section 7.7

Orbital Shapes and Energies

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39

• The periodic table is structured so that elements with the same type of valence electron configuration are

arranged in columns.

•The left-most columns include the alkali metals and the alkaline earth metals . In these elements the valence s

orbitals are being filled

• On the right hand side, the right-most block of six elements are those in which the valence p

orbitals are being filled

• In the middle is a block of ten columns that contain transition metals. These are elements in which d orbitals are

being filled

• Below this group are two rows with 14 columns. These are commonly referred to the f-block metals. In these

columns the f orbitals are being filled

Section 7.7

Orbital Shapes and Energies

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40

• The periodic table is structured so that elements with the same type of valence electron configuration are

arranged in columns.

Important facts to remember:

•2, 6, 10 and 14 are the number of electrons that can fill the s, p, d and f subshells (the l=0,1,2,3

azimuthal quantum number)

•The 1s subshell is the first s subshell, the 2p is the first p subshell

•3d is the first d subshell, and the 4f is the first f subshell

Section 7.7

Orbital Shapes and Energies

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Naming the sublevels

1s

2s 2p

3s 3p 3d

4s 4p 4d 4f

Section 7.7

Orbital Shapes and Energies

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Orbitals

Orbitals are regions of probability – each orbital can hold a maximum of 2 e-

The ‘s’ sublevel has 1 orbital

The ‘p’ sublevel has 3 orbitals

The ‘d’ sublevel has 5 orbitals

The ‘f’ sublevel has 7 orbitals

Section 7.7

Orbital Shapes and Energies

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Orbitals

Do you have to memorize this?

NOLook at the sublevel regions that you colored in on your

periodic table.

Section 7.7

Orbital Shapes and Energies

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Orbitals

Count how many electrons are in the ‘s’ sublevel

2

This means that since there are two electrons, and each orbital can hold two electrons, that there is only ONE orbital.

Section 7.7

Orbital Shapes and Energies

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Orbitals

Count how many electrons are in the ‘p’ sublevel

6

This means that since there are six electrons, and each orbital can hold two electrons, that there are THREE orbitals.

Section 7.7

Orbital Shapes and Energies

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Orbitals

Count how many electrons are in the ‘d’ sublevel

10

This means that since there are ten electrons, and each orbital can hold two electrons, that there are FIVE orbitals.

ORBITALS

Count how many electrons are in the ‘f’ sublevel

14This means that since there are fourteen

electrons, and each orbital can hold two electrons, that there are SEVEN orbitals.