c11 modern atomic theory

Chapter 11a

Modern Atomic Theory

Chapter 11

Table of Contents

2

11.1 Rutherford’s Atom11.2 Electromagnetic Radiation11.3 Emission of Energy by Atoms11.4 The Energy Levels of Hydrogen11.5 The Bohr Model of the Atom

Section 11.1

Rutherford’s Atom

Return to TOC

3

Nuclear Model of the Atom

• The atom has a small dense nucleus which is positively charged. contains protons (+1 charge). contains neutrons (no charge).

• The remainder of the atom is mostly empty space. contains electrons (–1

charge).

Section 11.1

Rutherford’s Atom

Return to TOC

Copyright © Cengage Learning. All rights reserved 4

• The nuclear charge (n+) is balanced by the presence of n electrons moving in some way around the nucleus.

• What are the electrons doing?• How are the electrons arranged and how do they move?

Section 11.2

Electromagnetic Radiation

Return to TOC

5

Characteristics

• Wavelength ( ) – distance between two peaks or troughs in a wave.

Section 11.2


Return to TOC

6

Different Wavelengths Carry Different Amounts of Energy

Section 11.2


Return to TOC

7

One of the ways that energy travels through space.

Section 11.2


Return to TOC

8

Characteristics

• Frequency ( ) – number of waves (cycles) per second that pass a given point in space

• Speed (c) – speed of light (2.9979×108 m/s)

= c 186,000 miles/s

Section 11.2


Return to TOC

9

Dual Nature of Light

• Wave• Photon – packet of energy

Section 11.2


Return to TOC

10

Characteristics

Ephoton = (hc) / λ

• Energy of a photon of light = Planck’s constant (h) (6.626 x 10-34Js) times the speed of light (c) (2.9979×108 m/s) divided by the wavelength in meters (λ) or the wavelength in nanometers (nm) times ten to the -9 power (550nm = 550 x 10-9m).

OR:

Section 11.2


Return to TOC

11

Let’s Practice!

What is the energy of light with a wavelength of 535 nm?

E=hc/λ

=6.626 x 10-34Js(3.00 x 108m/s)/(535 x 10-9m)

=3.70 x 10-19 J

Section 11.2


Return to TOC

Seeing the Light-A New Model of the AtomMaxwell Planck-Black Body Radiation

Found that blackbody radiation was quantized.

1900—Nobel Prize in 1918

Section 11.2


Return to TOC

13

Quantized Energy Levels

• The energy levels of all atoms are quantized.

Section 11.2


Return to TOC

Einstein’s Photoelectric Effect (1905--Nobel Prize in 1921)

Only light from a certain color (energy) could eject electrons. Intensity of the light had no effect. Energy is absorbed only at quantized energies!

Section 11.3

Emission of Energy by Atoms

Return to TOC


Atoms can give off light. They first must receive energy and become excited. The energy is released in the form of a photon. The energy of the photon corresponds exactly to the energy change experienced by the emitting atom.

Section 11.4

The Energy Levels of Hydrogen

Return to TOC


• Atomic states Excited state – atom with excess energy Ground state – atom in the lowest possible state

• When an H atom absorbs energy from an outside source it enters an excited state.

Section 11.4


Return to TOC


Energy Level Diagram

• Energy in the photon corresponds to the energy used by the atom to get to the excited state.

Section 11.4


Return to TOC

Stokes Shift-Absorb high energy (UV) and emit low energy (visible).

18

Section 11.4


Return to TOC

19

• Only certain types of photons are produced when H atoms release energy. Why?

Section 11.4


Return to TOC

Line Spectra

http://jersey.uoregon.edu/vlab/elements/Elements.html

Section 11.4


Return to TOC

21

The word laser comes fromlight amplification by stimulated emission of radiation.

Section 11.4


Return to TOC

22

Lasers used to remove blood clots.Laser light transmitted in fiber optics.Cataract RemovalLight Shows

Lasers

Section 11.4


Return to TOC

23

Holograms3D pictures made by Lasers using the interference pattern between reflected laser light from the surface of an object and the undisturbed laser light reflected from a mirror. The Interference pattern is recorded on film. The developed film can then be used by a laser to recreate the image in 3D.

http://www.youtube.com/watch?v=wrxUYzWASvE

http://www.youtube.com/watch?v=E4A_u67EKnU&feature=fvw

http://www.youtube.com/watch?v=mcSYpZchFpI

https://www.youtube.com/watch?v=49BhZlQvjLw

https://www.youtube.com/watch?v=89KxxpmMhi4

Section 11.4


Return to TOC

The Doppler Effect

The doppler effect is the apparent change in frequency of a wave due to the relative motion of the listener and the source of the sound.

The doppler effect also occurs in light waves and is used by astronomers to calculate the speed at which stars are approaching or receding.

Section 11.4


Return to TOC

25

Bohr Model

Line Spectra in Stars and the red shift indicating movement away or towards us.

7 -

Section 11.4


Return to TOC


Quantized Energy Levels

• Since only certain energy changes occur the H atom must contain discrete energy levels.

Section 11.4


Return to TOC

27

Concept Check

Why is it significant that the color emitted from the hydrogen emission spectrum is not white?

How does the emission spectrum support the idea of quantized energy levels?

Section 11.4


Return to TOC


Concept Check

When an electron is excited in an atom or ion

a) only specific quantities of energy are released in order for the electron to return to its ground state.b) white light is never observed when the electron returns to its ground state.c) the electron is only excited to certain energy

levels.d) All of the above statements are true when an electron is excited.

Section 11.5

The Bohr Model of the Atom

Return to TOC

29

• Quantized energy levels• Electron moves in a circular

orbit.• Electron jumps between

levels by absorbing or emitting a photon of a particular wavelength.

• Actually electrons do not move in a circular orbit.

Niels Bohr1913—Nobel Prize in 1922

Niels Bohr hypothesized that electrons orbit the nucleus just as the planets orbit the sun (planetary model).

Section 11.5


Return to TOC

30

D

Chapter 11bModern Atomic Theory

Section 11.5


Return to TOC

31

11.6 The Wave Mechanical Model of the Atom11.7 The Hydrogen Orbitals11.8 The Wave Mechanical Model: Further Development11.9 Electron Arrangements in the First Eighteen Atoms on

the Periodic Table11.10 Electron Configurations and the Periodic Table11.11 Atomic Properties and the Periodic Table

Chapter 11

Modern Model of the Atom

Section 11.6

The Wave Mechanical Model of the Atom

Return to TOC

32

Orbitals• Nothing like orbits• Probability of finding the electron within a certain space• This model gives no information about when the electron

occupies a certain point in space or how it moves.

Section 11.7

The Hydrogen Orbitals

Return to TOC


Orbitals• Orbitals do not have sharp boundaries and are

represented by probability distributions or where the electron is likely to be found without regards to movement of the electrons.

• Chemists arbitrarily define an orbital’s size as the sphere that contains 90% of the total electron probability.

Section 11.6


Return to TOC

34

Scanning Tunneling Microscope

Kx9GeA7false

Section 11.6


Return to TOC

Louis DeBroglie

• He found that matter (electrons) moved in waves. Just as light behaved like particles and waves, so did matter.

• An 18-wheeler moving down Hwy 99 at 60mph has a wavelength smaller than an atom.

• However, an electron (very light) moves much faster and its wavelength is much larger than its size.

1924 – Nobel Prize in 1929

Section 11.6


Return to TOC

Probability of Finding Electrons Like Fireflies

Section 11.7


Return to TOC

37

Hydrogen Energy Levels

• Hydrogen has discrete energy levels. Called principal energy

levels Labeled with whole

numbers

Section 11.7


Return to TOC



• Each principal energy level is divided into sublevels. Labeled with numbers and letters Indicate the shape of the orbital

Section 11.7


Return to TOC



• The s and p types of sublevel

Section 11.7


Return to TOC

40

d Orbitals

7 -

Section 11.7


Return to TOC

41

f-orbtals

Section 11.7


Return to TOC

42

Why the different shapes?

1s 3s2s2px

3pz

3d2py

2pz

3py

3px

Section 11.7


Return to TOC

43

Orbital Labels

1. The number tells the principal energy level. 2. The letter tells the shape.

The letter s means a spherical orbital or shape of the probability distribution of the electron.

The letter p means the orientation. The x, y, or z subscript on a p orbital label tells along which of the coordinate axes the two lobes lie.

Section 11.7


Return to TOC

44

Hydrogen Orbitals

• Why does an H atom have so many orbitals and only 1 electron? An orbital is a potential space for an electron. Atoms can have many potential orbitals.

Section 11.8

The Wave Mechanical Model: Further Development

Return to TOC

45

Atoms Beyond Hydrogen

• The Bohr model was discarded because it does not apply to all atoms. It did not consider the different energy sublevels or suborbitals within each orbital.

• Atoms beyond hydrogen have multiple electrons that distorts the energy levels due to electron-electron interactions.

• Need one more property to determine how the electrons are arranged: Spin – electrons spin like a top causing a magnetic field. Opposite magnetic fields can attract allowing electrons to occur in pairs if their spin or magnetic field is opposite.

Section 11.8


Return to TOC

46

Atoms Beyond Hydrogen• Pauli Exclusion Principle – an atomic orbital

can hold a maximum of 2 electrons and those 2 electrons must have opposite spins.

Section 11.8


Return to TOC


Principal Components of the Wave Mechanical Model of the Atom

1. Atoms have a series of energy levels called principal energy levels (n = 1, 2, 3, etc.).

2. The energy of the level increases as the value of n increases.

3. Each principal energy level contains one or more types of orbitals, called sublevels.

4. The number of sublevels present in a given principal energy level equals n.

Section 11.8


Return to TOC



5. The n value is always used to label the orbitals of a given principal level and is followed by a letter that indicates the type (shape) of the orbital (1s, 3p, etc.).

6. An orbital can be empty or it can contain one or two electrons, but never more than two. If two electrons occupy the same orbital, they must have opposite spins.

Section 11.8


Return to TOC

49


7. The shape of an orbital does not indicate the details of electron movement. It indicates the probability distribution for an electron residing in that orbital.

Section 11.8


Return to TOC


Concept Check

Which of the following statements best describes the movement of electrons in a p orbital?a) The electron movement cannot be exactly

determined.b) The electrons move within the two lobes of the p orbital, but never beyond the outside surface of

the orbital.c) The electrons are concentrated at the center

(node) of the two lobes.d) The electrons move along the outer surface of the p orbital, similar to a “figure 8” type of movement.

Section 11.8


Return to TOC

51

Energy Level Diagram for

Carbon

Section 11.9Electron Arrangements in the First Eighteen Atoms on the Periodic Table

Return to TOC


H Atom

• Electron configuration – electron arrangement 1s1

• Orbital diagram – orbital is a box grouped by sublevel containing arrow(s) to represent electrons


Return to TOC


Li Atom

• Electron configuration1s2 2s1

• Orbital diagram


Return to TOC


O Atom

• The lowest energy configuration for an atom is the one having the maximum number of unpaired electrons in a particular set of degenerate (same energy) orbitals.

Oxygen: 1s 2s 2p


Return to TOC


• The electron configurations in the sublevel last occupied for the first eighteen elements.


Return to TOC

56

Classifying Electrons

• Core electrons – inner electrons• Valence electrons – electrons in the outermost (highest)

principal energy level of an atom 1s22s22p6 (valence electrons = 8) The elements in the same group on the periodic table

have the same valence electron configuration. Elements with the same valence electron

arrangement show very similar chemical behavior.


Return to TOC


Concept Check

How many unpaired electrons does the element cobalt (Co) have in its lowest energy state?

a) 0b) 2c) 3d) 7

3d suborbitals


Return to TOC


Concept Check

Can an electron in a phosphorus atom ever be in a 3d orbital? Choose the best answer.

a) Yes. An electron can be excited into a 3d orbital.b) Yes. A ground-state electron in phosphorus is located in a 3d orbital.c) No. Only transition metal atoms can have

electrons located in the d orbitals.d) No. This would not correspond to phosphorus’ electron arrangement in its ground state.


Return to TOC

59

Quantum #’s are like an Address. What do you need to know to find out where you live?

State City Street House

Principle Quantum # (n)

Angular Quantum # (l)

Magnetic Quantum # (ml)

Spin Quantum # (ms)

Section 11.10

Electron Configurations and the Periodic Table

Return to TOC


• Look at electron configurations for K through Kr.

Section 11.10


Return to TOC


Orbital Filling and the Periodic Table

Section 11.10


Return to TOC


Orbital Filling

1. In a principal energy level that has d orbitals, the s orbital from the next level fills before the d orbitals in the current level.

2. After lanthanum, which has the electron configuration [Xe]6s25d1, a group of fourteen elements called the lanthanide series, or the lanthanides, occurs. This series of elements corresponds to the filling of the seven 4f orbitals.

Section 11.10


Return to TOC

63

Orbital Filling

3. After actinum, which has the configuration [Rn]7s26d1,a group of fourteen elements called the actinide series, or actinides, occurs. This series corresponds to the filling of the seven 5f orbitals.

Section 11.10


Return to TOC

64

Orbital Filling

4. Except for helium, the group numbers indicate the sum of electrons in the ns and np orbitals in the highest principal energy level that contains electrons (where n is the number that indicates a particular principal energy level). These electrons are the valence electrons.

Section 11.10


Return to TOC


Exercise

Determine the expected electron configurations for each of the following.

a) S 1s22s22p63s23p4 or [Ne]3s23p4

b) Ba [Xe]6s2

c) Eu [Xe]6s24f6

Section 11.10


Return to TOC


• Write electron configurations for the following:1. Al2. Sc3. K4. Br5. Zn6. Hg

7 -

1s22s22p63s23p1

1s22s22p63s23p64s23d1

1s22s22p63s23p64s1

1s22s22p63s23p64s23d104p5

1s22s22p63s23p64s23d10

1s22s22p63s23p64s23d104p65s24d105p66s2 4f145d10

Section 11.10


Return to TOC


• Write the abbreviated electron configuration for the following:1. Magnesium2. Carbon3. Boron4. Chlorine5. Selenium

7 -

– [Ne] 3s23p5

– [Ne] 3s2

– [He] 2s22p2

– [He] 2s22p1

– [Ar] 4s23d104p4

Section 11.10


Return to TOC


• Write the electron configuration in long and abbreviated notation for the following ions.1. Br-

2. N3-

3. K+

4. Sr2+

5. S2-

6. Ni2+

7 -

[Kr] isoelectronic with Kr[Ne] isoelectronic with Ne[Ar] isoelectronic with Ar[Kr] isoelectronic with Kr[Ar] isoelectronic with Ar[Ar]4s23d6 isoelectronic with Fe

Section 11.10


Return to TOC

69

Section 11.11

Atomic Properties and the Periodic Table

Return to TOC


Metals and Nonmetals

• Metals tend to lose electrons to form positive ions.• Nonmetals tend to gain electrons to form negative ions.

Section 11.11


Return to TOC


Ionization Energy

• Energy required to remove an electron from a gaseous atom or ion. X(g) → X+(g) + e–

Mg → Mg+ + e– I1 = 735 kJ/mol (1st IE)

Mg+ → Mg2+ + e– I2 = 1445 kJ/mol (2nd IE)

Mg2+ → Mg3+ + e– I3 = 7730 kJ/mol *(3rd IE)

*Core electrons are bound much more tightly than valence electrons.

Section 11.11


Return to TOC


Ionization Energy

• In general, as we go across a period from left to right, the first ionization energy increases.

• Why? Electrons added in the same principal

quantum level do not completely shield the increasing nuclear charge caused by the added protons.

Electrons in the same principal quantum level are generally more strongly bound from left to right on the periodic table.

Section 11.11


Return to TOC

73

Ionization Energy

• In general, as we go across a period the ionization energy increases.

• As we go up a group from top to bottom, the first ionization energy increases.

Section 11.11


Return to TOC


Concept Check

Which atom would require more energy to remove an electron? Why?

Na Cl

Section 11.11


Return to TOC


Concept Check

Which atom would require more energy to remove an electron? Why?

Li Cs

Section 11.11


Return to TOC


Atomic Size

• In general as we go across a period from left to right, the atomic radius decreases. Effective nuclear charge increases, therefore

the valence electrons are drawn closer to the nucleus, decreasing the size of the atom.

• In general atomic radius increases in going down a group. Orbital sizes increase in successive principal

quantum levels.

Section 11.11


Return to TOC


Relative Atomic Sizes for Selected Atoms (Fig. 11-36)

Section 11.11


Return to TOC

78

Concept Check

Which should be the larger atom? Why?Na Cl

Section 11.11


Return to TOC


Concept Check

Which should be the larger atom? Why?Li Cs

Section 11.11


Return to TOC


Concept Check

Which is larger?• The hydrogen 1s orbital• The lithium 2s orbitalWhich is lower in energy?•The hydrogen 1s orbital•The lithium 2s orbital

Section 11.11


Return to TOC


Exercise

Arrange the elements oxygen, fluorine, and sulfur according to increasing:

Ionization energy S, O, F

Atomic size F, O, S

c11 modern atomic theory

Documents