Download Unit 8: Electron Configuration

Electron Configuration
• Nucleus is (+) because it is composed of
neutrons (0) and protons (+).
• Atoms = neutral, therefore #p (+) = #e- (-).
• Electrons determine the chemical properties of
an atom.
• Nucleus changes during nuclear reactions, but
remains unchanged during chemical and physical
changes.
• Electrons do not get away because the (-) charge
is attracted to the (+) nucleus.
• We need a model to describe e- behavior.
• Balmar (1887) - excited gas atoms with
electricity.
Draw diagram on the board.
• The light/photograph lets us know what is
going on inside the atom.
Electromagnetic spectrum
Draw the spectrum on the board.
• Electromagnetic radiation are forms of
energy that travel through space as waves.
• The part of the spectrum that we are going to
look at in more detail is the visible end.
• When the light of the visible end of the
spectrum is passed through a prism and we take a
photograph we can get 2 types of spectra:
1) Bright line spectra - only certain colors are
emitted. This type of spectra produces discrete
lines.
(ex) elements
Draw diagram on the board.
2) Continuous spectra - no discrete lines, a smear
or blend of colors, a bunch of lines.
(ex) sun, white light.
Draw diagram on the board.
Light (radiant energy) = electromagnetic
radiation
•Behaves as waves.
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•Moves at the rate of 3.00 X10 m/sec (speed of
light) = C.
We describe light as a wave with a:
A) Frequency (V) - number of cycles or peaks
per second.
Units: (cycles/sec) = hertz
B) Wavelength (
) - distance from peak to
peak.
C) Speed - (C) - all light has the same speed =
3.00 X 108 m/s
3.00 X 1010 cm/s
• In one sec light can travel around the earth 7 X.
D) Energy (E)
Give equations and tell how the variables are
related
Constants, units, and conversions for
problems:
h = Planck’s constant = 1.58 X 10-37 kcalXsec
• calorie (cal) - the amount of energy needed to
raise 1 g of water 1 C.
• electron volt (ev) - a unit of energy.
1 ev = 3.85 X 10-17 kcal
1 m = 1 X 10 9 nm
1 cal = 4.18 J
• Photon or quanta of light - a packet of energy.
• Electrons absorb and emit energy in certain
amounts to get from one level to another =
photons or quanta of light.
Do examples of energy, wavelength, and frequency problems.
•Quantum Mechanics
•Why does an excited atom emit only certain
amounts of energy?
Neils Bohr (1913) - Theory of Electron Behavior
1) Electrons are like planets - they orbit the
nucleus in certain circular paths - INCORRECT!
2) Electrons can only have certain amount of
energy - TRUE! Quanta or photons.
3) Electrons in orbit will not lose energy due to
radiation: (+) nucleus holds e-(-) in place - TRUE!
4) Electrons pick up enough energy to get exactly
to another orbit. Then they emit the asorbed energy
in the form of light and return to their original orbit
- TRUE!
How does Bohr explain spectral lines?
Since e- can only pick up certain amounts of
energy (quanta or photons of energy) to get
exactly to another energy level they can only emit
certain amounts of energy as well. That is why we
can only see certain colors at certain wavelengths.
Things to know:
• Electrons only give off energy when they return
to a lower energy level.
• Highest probablity of finding an electron is in
the electron cloud where it is most dense.
• The position of the electron can be represented
by a cloud.
• Electrons behave as particles and waves.
• All chemical behavior centers around the
behavior of the electrons (specifically the valence
= outer shell electrons).
Electron Behavior
(1) energy level (n) - a group of electrons with
the same amount of energy (not a place).
n = 1,2,3,4,5,6,7
• Electrons can only have seven different amounts
of energy = energy levels.
• Energy level = shell = k,l,m,n,o,p,q
• Energy level = Principle quantum number.
• 1st energy level is the lowest in en - closest to
the nucleus.
• 7th energy level is the highest in en - furthest
from the nucleus.
• Each energy level has a maximum # of e- it can
hold called the maximum capacity = 2n2 - square n
first!
Put diagram on the board.
Analogy: Parking lot
• Cars (e-) not allowed to stop
• Travel at certain speeds (5,10,15 m/hr) = en
• No in between speeds (en)
• None one leave the lot.
• May take any path, only speed (energy) is
restricted.
2) subshell or sublevels = ways electrons carve
out space or the path of the electron.
• Basically 4 ways that electrons carve out space =
s,p,d,f
• e- in an s carve out space in a spherical shape.
• p e- carve out space like a figure 8 or 2 footballs
pointing toward the nucleus.
•The shape of the d and f subshell are 3-D and are
very complex!
• Each subshell also has a maximum capacity:
s = 2 ep = 6 ed = 10 ef = 14 eAdd this to the chart.
How do 1s and 2s e- differ?
They both carve out space in a sphere, but a 2s ehas more energy than a 1s e- and therefore is
further from the nucleus.
3) Spin
• e- spin like tops.
• They spin in 2 possible directions.
draw this on the board.
• 2 e- with opposite spins set up a slight magnetic
field which allows the electrons which are like in
charge (-) and would normally repel to attract.
4) Orbital - a region in space that can hold a
maximum of 2 electrons with equal but opposite
spins.
Draw an s, p, d, and f orbital.
Arrangement of electrons = Electron
configuration
• Very important because it determines the
chemical properties of the element.
• Basic law of nature: things seek positions of
lowest energy, therefore we would expect the 1st en
level to fill, then the 2nd, 3rd, 4th, and so on.
• Nearly true, but some complications.
• Energy levels do not completely fill before the
next one starts to fill.
• Often small subshells of higher en levels are
filled before large subshells of lower en levels.
• Electrons fill up the atom according to arrows (no
need to memorize!)
Pass out chart and do some examples (Zn) and point
out that 4s fills before 3d.
Other ways to show order of occupancy
1) Bracket diagrams
Give examples
2) Lewis Dot diagrams (show only valence e-).
Give examples
3) Orbital notation
Give examples.
Stable (unreactive) vs. unstable (reactive)
Stable outer shell arrangements:
1s2
octet
an octet plus a filled subshell
Show these on the board.
• Any other arrangement is reactive or unstable.
Wave mechanical view of the atom
Heisenberg, de Broglie, and Schrodinger helped
to develop a theory of atomic structure.
• Electrons do not have paths like the planets,
therefore it is impossible to determine the exact
location of an electron at any given time.
Heisenberg’s Uncertainy Principle: It is
impossible to know both the position and the
momentum of an e- at the same time.
Schrodinger’s equation - dev. an equation to tell
where the electron is at a given point in time.
Quantum numbers
• These are the variables that go into Schrodinger’s
eq.
• Pauli exclusion principle: no 2 e- can have the
same 4 quantum numbers.
1) Principle quantum # (n) - indicates the most
probable distance of the e- from the nucleus.
Relates to the overall en of the e-.
n = 1,2,3,4,5,6,7
2) Angular momentum quantum number (l) relates to the shape or the volume that the wave is in
(subshell).
l = 0 -----> (n-1)
3) magnetic quantum number (ml) - related to the
direction in space or the orientation (# of orbitals)
ml = -l -----> 0 -----> +l
4) spin quantum number (ms) - spin
Ms = +1/2 and -1/2
Do example if n = 4