1. Quantum Theory

2. Electromagnetic Spectrum
Visible spectrum
HIGH
ENERGY
Violet
Blue
Green
Yellow
Orange
Red
LOW
ENERGY
400 nm
500 nm
600 nm
700 nm
White
Light
g rays
X-rays
Ultraviolet
Infrared
Microwave
Radio waves
Radar TV FM
Short
Wave
Long
Wave
Water waves transmit energy through space by the periodic oscillation of matter.
• Energy that is transmitted, or radiated, through space in the form of periodic oscillations of an electric and a magnetic field is called electromagnetic radiation.
Electromagnetic radiation
– Consists of two perpendicular waves, one electric and one magnetic, propagates at the speed of light, abbreviated c, and has a value of x 108 m/s
– Is radiant energy that includes radio waves, microwaves, visible light, X -rays, and gamma rays
– Various kinds of electromagnetic radiation all have the same speed (c) but differ in wavelength and frequency
– Frequency of electromagnetic radiation is inversely proportional to the wavelength
c =  or  = c/
– Energy of electromagnetic radiation is directly proportional to its frequency (E  ) and inversely proportional to its wavelength (E  1/)
10-2nm
10-1nm
100nm
101nm
102nm
103nm
10-3cm
10-2cm
10-1cm
100cm
101cm
1cm
101m
102m
103m
104m
Wavelength, l
1019Hz
1018Hz
1017Hz
1016Hz
1015Hz
1014Hz
1013Hz
1012Hz
1011Hz
1010Hz
109Hz
100 MHz
10 MHz
1 MHz
100 KHz
Frequency, n
Electromagnetic spectrum
Davis, Frey, Sarquis, Sarquis, Modern Chemistry 2006, page 98

3. Photoelectric Effect Light is a form of energy
Light can hit a metal surface and cause the metal to emit electrons
The photoelectric effect
Light travels in waves
Light at any frequency can hit a metal surface and cause the metal to emit electrons

4. Photoelectric Effect

5. Photoelectric Effect
Light
Nucleus
Metal
A metal did not emit electrons when certain frequencies of light hit it When red light strikes a metal surface, no electrons are ejected.

6. Photoelectric Effect
Light
Electron
Nucleus
Metal
There was a minimum frequency of light needed to get a metal to emit electrons When green light strikes a metal surface, electrons are ejected.

7. Planck’s Explanation
If electromagnetic radiation acted as a wave, then it would emit energy continuously
Instead, electromagnetic radiation is emitted in small specific amounts
Called quanta
AKA: Things come in chunks
Quantum: the minimum energy that can be lost or gained by an atom

8. Continuous vs. Quantized
A B
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 330

9. Einstein’s Explanation
Built off of Planck’s ideas
Agreed that electromagnetic radiation would emit energy continuously if it acted as a wave
Agreed that electromagnetic radiation emits quanta

10. Einstein’s Explanation
Noticed that electromagnetic radiation is sometimes continuous and sometimes quantized
Proposed a dual wave-particle nature of electromagnetic radiation
Light has wavelike properties
Light can be thought of as a stream of particles

11. Einstein’s Explanation
Defined the term photon
A particle of electromagnetic radiation (light) that has no mass and carries a quantum (bundle) of energy
In order for the photoelectric effect to occur
The metal is struck by photons
Each photon must carry a certain amount of energy in order to knock an electron loose from the metal

12. 5.1
The Bohr Model
Bohr proposed that an electron is found only in specific circular paths, or orbits, around the nucleus.

13. Bohr Model of Hydrogen Nucleus Possible electron orbits e e
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 331

14. 5.1
The Bohr Model
Each possible electron orbit in Bohr’s model has a fixed energy.
The fixed energies an electron can have are called energy levels.
A quantum of energy is the amount of energy required to move an electron from one energy level to another energy level.

15. 5.1
The Bohr Model
Like the rungs of the strange ladder, the energy levels in an atom are not equally spaced.
The higher the energy level occupied by an electron, the less energy it takes to move from that energy level to the next higher energy level.
These ladder steps are somewhat like energy levels. In an ordinary ladder, the rungs are equally spaced. The energy levels in atoms are unequally spaced, like the rungs in this ladder. The higher energy levels are closer together.

16. The Quantum Mechanical Model
5.1
The Quantum Mechanical Model
The propeller blade has the same probability of being anywhere in the blurry region, but you cannot tell its location at any instant. The electron cloud of an atom can be compared to a spinning airplane propeller.
The electron cloud of an atom is compared here to photographs of a spinning airplane propeller. a) The airplane propeller is somewhere in the blurry region it produces in this picture, but the picture does not tell you its exact position at any instant. b) Similarly, the electron cloud of an atom represents the locations where an electron is likely to be found.

17. The Quantum Mechanical Model
5.1
The Quantum Mechanical Model
In the quantum mechanical model, the probability of finding an electron within a certain volume of space surrounding the nucleus can be represented as a fuzzy cloud. The cloud is more dense where the probability of finding the electron is high.
The electron cloud of an atom is compared here to photographs of a spinning airplane propeller. a) The airplane propeller is somewhere in the blurry region it produces in this picture, but the picture does not tell you its exact position at any instant. b) Similarly, the electron cloud of an atom represents the locations where an electron is likely to be found.

18. 5.1
Atomic Orbitals
An atomic orbital is often thought of as a region of space in which there is a high probability of finding an electron.
Each energy sublevel corresponds to an orbital of a different shape, which describes where the electron is likely to be found.

19. 5.1
Atomic Orbitals
Different atomic orbitals are denoted by letters. The s orbitals are spherical, and p orbitals are dumbbell-shaped.
The electron clouds for the s orbital and the p orbitals are shown here.

20. 5.1
Atomic Orbitals
Four of the five d orbitals have the same shape but different orientations in space.
The d orbitals are illustrated here. Four of the five d orbitals have the same shape but different orientations in space. Interpreting Diagrams How are the orientations of the dxy and dx2 – y2 orbitals similar? How are they different?

21. Vocabulary
Orbital
The space around a nucleus that has a high probability of finding an electron
Simply a probability graph of where we can find an electron
Quantum numbers: tell us the properties of atomic orbitals and the properties of electrons in the orbitals
Principle quantum number
Symbol: n
The energy level that an electron occupies
Angular momentum quantum number
Symbol: l
The shape of the orbital
Spin quantum number
+1/2 or -1/2
Spin state of an electron