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.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.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.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.Draw diagram on the board.

Light (radiant energy) = electromagnetic radiation

•Behaves as waves.

•Moves at the rate of 3.00 X108 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 Give equations and tell how the variables are relatedrelated

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, andDo examples of energy, wavelength, and frequency problems.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.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 e-

p = 6 e-

d = 10 e-

f = 14 e-

Add this to the chart.Add this to the chart.

How do 1s and 2s e- differ?

They both carve out space in a sphere, but a 2s e- has 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 boarddraw 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.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 Pass out chart and do some examples (Zn) and point out that 4s fills before 3d.point out that 4s fills before 3d.

Other ways to show order of occupancy

1) Bracket diagrams

Give examplesGive examples

2) Lewis Dot diagrams (show only valence e-).

Give examplesGive examples

3) Orbital notation

Give examples.Give examples.

Stable (unreactive) vs. unstable (reactive)

Stable outer shell arrangements:

1s2 octet an octet plus a filled subshell

Show these on the board.Show these on the board.

• Any other arrangement is reactive or unstable..

Wave mechanical view of the atom

Heisenberg, de Broglie, and SchrodingeSchrodinger 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 = 4Do example if n = 4