photochemistry PPT

1. Models of the
Atom

2. Bohr’s model…
• Electrons are found in specific
circular paths (orbits) around the
nucleus.
• The electrons have fixed energies
called energy levels. (like rungs on a
ladder)
• The amount of energy required to
move an electron to another energy
level is called a quantum.

3. The Quantum Mechanical model
• It is based on the energy and possible
location of an electron.
• how likely it is to find an electron is
described in terms of probability. (ie.
Propeller blades)
• Based on work done by Shrodinger…

5. Atomic Orbitals
• The energy levels of electrons are labeled
by principal quantum numbers (n)
• Each energy sublevel corresponds to an
orbital of a different shape, which describes
where the electron is likely to be found.

6. Atomic Orbitals

7. Shapes and
Orientations of
Orbitals

8. 1s Orbital
• Sphere around the nucleus
The one tells you that the electron
is in the orbital closest to the
nucleus
• S tells you about the shape

9. 2s Orbital
• Similar to 1s except the electron is most
likely in the region farther from the nucleus

10. p Orbitals
• At the first energy level there is only the 1s
orbital, after the second energy level there
are 2p orbitals
• Look like dumbbells
• In the three directions

14. Remember….
MAX NUMBER OF ELECTRONS
IN AN ENERGY LEVEL
ENERGY LEVEL MAX # OF ELECTRONS
1 2
2 8
3 18
4 32
5 50

15. Electron
Configuration
A detailed way of showing the
order in which electrons fill in
around the nucleus

16. Electron Configuration
Symbols
1s2
Energy Level
Sub Level
(s, p, d, f )
# of e- in
sub level

17. We must follow 3 rules…
• Aufbau priciple
• Electrons occupy energy levels with lowest
energy first.

18. Pauli exclusion principle
• If 2 electrons occupy the same energy level
they must have opposite spins.

19. Hund’s rule…
• Electrons that occupy orbitals of the same
energy will have the maximum number of
electrons with the same spin.
• 2p

20. To start we will use orbital filling
diagrams to help us with electron
configurations….
• Example
Boron- has 5 electrons

21. Periodic table arrangement
• the quantum theory helps to explain the
structure of the periodic table.
• n - 1 indicates that the d subshell in period 4
actually starts at 3 (4 - 1 = 3).
s (n) d (n - 1) p (n)
1
2
3
4
5
6
7
f (n -2)

22. Summary: p orbitals and d orbitals
p orbitals look like
a dumbell with 3
orientations: px,
py, pz (“p sub z”).
Four of the d orbitals resemble two dumbells in a
clover shape. The last d orbital resembles a p
orbital with a donut wrapped around the middle.

23. 1st Quantum #
Principle Quantum #
(n)
Specifies the energy level
that the electron is on.

24. 2nd Quantum #
Specifies the shape of the
sub level .
(l)

25. The 3rd (m) and 4th quantum
numbers (s) …
• Deals with the orbital within the sublevel
and the spin of the electron.

26. Four Energy Sub-Levels
Energy Level Sub-level Type of sub # of
Orbitals
s Sphere 2 1
p Dumbbell 6 3
d 4-Lobed 10 5
f 6-8 Lobed 14 7