1. Chapter 4
September 21, 2011

2. Properties of Light
Light is a kind of electromagnetic radiation: form of energy that exhibits wavelike behavior as it travels through space
Electromagnetic spectrum: all the forms of electromagnetic radiation

3. The Electromagnetic Spectrum

4. Properties of Light
Wavelength (λ)- the distance between corresponding points on adjacent waves
(units: meter, cm, nanometer)
Frequency (v) the number of waves that pass a given point in a specific time
(units: hertz)
c= λv
c= speed of light

5. The Photoelectric Effect
End at 2:00.

6. The Photoelectric Effect The Particle Nature of Light
Wave theory: light of any frequency would supply enough energy The experiment showed it needed a minimum frequency to eject electrons

7. Light has wavelike and particle-like properties
Plank deduced that energy is given off in small, specific quantities called quanta
Quantum: the minimum quantity of energy that can be lost or gained by an atom
E=hv
E= Energy (joules) of quantum radiation
H= Plank’s constant x 10-34
v= frequency of radiation emitted
Photon: particle of electromagnetic radiation having zero mass and carrying quantum of energy (Einstein)

8. Einstein Says…
Electromagnetic radiation is absorbed by matter only in whole numbers of photons
Minimum Energy= minimum frequency of photon to knock electron off metal
Frequency< required energy (electron remains bound)
Frequency> minimum energy (electron is ejected from metal surface)

9. Ground vs. Excited State
Ground State: Lowest energy state of an atom
Excited State: A state in which an atom has a higher potential energy than it has in its ground state
Dropping from an excited state to ground state- gives off the energy gained in the form of electromagnetic radiation

10. Hydrogen-Atom Line Emission Spectrum
Vacuum with hydrogen gas at low pressure→ pinkish glow
Narrow beam of light shined through prism → specific frequencies (wavelengths) of visible light

11. Stumped Expected: continuous spectrum
Why? Because it was predicted that Hydrogen would be excited by any amount of energy added to it
Observed: specific frequencies of light

12. Justification Ephoton= E3-E2
1913 Niels Bohr hypothesis: electron can circle the nucleus only in an allowed path called an orbit, and when in an orbit the electron displays a fixed energy

13. Orbits are like a Ladder
An electron can only be in one orbit or another- NOT inbetween
You can only stand on one rung of a ladder or the one above it- not in the middle of the two

14. Energy Transitions

15. Section 4.2 The Quantum Model of the Atom
Just like light, electrons have a wave-particle nature
Heisenberg Uncertainty Principle: it is impossible to determine simultaneously both the position and velocity of an electron or any other particle
Quantum Theory: describes mathematically the wave properties of electrons and other very small particles.

16. How do Electrons Travel?
Electrons do NOT travel around the nucleus in neat orbits
Electrons exist in regions called orbitals: 3 dimensional region around the nucleus that indicates the probable location of an electron
Not in neat orbits!

17. Energy Levels
As you increase in rows, an electron’s energy and distance from nucleus increases

18. Shape of the orbitals

19. Energy Levels + Orbitals
1st energy level: 1 sublevel: s orbital (only)
2nd energy level: 2 sublevels: s and p orbitals
3rd energy level: 3 sublevels: s, p, d orbitals
4th energy level: 4 sublevels: s, p, d, f orbitals
1st energy level
2ndenergy level
Energy increases as you increase energy levels
3rd energy level
4th energy level

20. Naming energy levels + sublevel
S orbital
D orbitals
P orbitals
F orbitals

21. Number of Orbitals per Sublevel
1 s orbital per sublevel
3 p orbitals (x, y, z axis) in each sublevel
5 d orbitals in each sublevel
7 f orbitals in each sublevel

22. Spin Quantum Number A single orbital can hold a maximum of 2 electrons
Let’s do some math!
The s sublevel has ________ orbital per main energy level 1 2
Therefore, the s sublevel contains ______ electrons per main energy level 3
The p sublevel has ________ orbital per main energy level 6
The p sublevel has ________ electrons per main energy level
The d sublevel has ________ orbital per main energy level 5 10
The d sublevel has ________ electrons per main energy level

23. Practice Get out your periodic table
Identify the main energy levels, 1, 2, 3, 4
Identify the s, p, d blocks (where those sublevels are)
What elements are in the 2 s position?
What sublevel is Zinc-65 in?
What main energy level and sublevel is phosphorus in?
What main energy level and sublevel is calcium in?

24. Periodic Table

25. 4.3 Electron Configuration
Rules:
Aufbau Principle: an electron occupies the lowest- energy orbital it can receive
Hund’s Rule: orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron

26. Orbital Notation
How many electrons are in Boron? What is the orbital notation
Boron: Electron Configuration 1s22s22p1
Number of electrons: count the exponents
Electrons=5
Orbital Notation:

27. A new look at things…

28. Inner-Shell Electrons
First energy level can hold a maximum of 2 electrons
2, 3, 4 energy levels etc. can hold up to 8 electrons

29. Valence Electrons
Valence Electrons: electrons in the outermost shell that can participate in the formation of chemical bonds with other atoms
To figure out valence electrons:
Group 1= 1 valence electron
Group 2=2 valence electrons
Group 13= 3 valence electrons
Group 14=4 valence electrons
Group 15= 5 valence electrons
Group 16= 6 valence electrons
Group 17= 7 valence electrons
Group 18= 8 valence electrons
P block
Group 13-10= valence electrons

30. Practice Valence Electrons
How many valence electrons are in each of the following elements?
Lithium
Carbon
Helium
Chlorine
Tellerium (Te)
Calcium
Nickel 1 4 2 7 6 2 2

31. Lewis Dot Structures

32. Practice Lewis Structures
Lithium
Carbon
Helium
Chlorine
Tellerium (Te)
Calcium
Nickel

33. Electron Configuration Notation
Helium:
Lithium:
Boron:
Carbon:
Neon:
Sodium:
1s22s22p2
1s22s22p6
1s22s22p63s1

34. Noble Gas Configuration
Sodium: OR
1s22s22p63s1
[Ne]3s1
Noble Gas Configuration