Transcript Atomic theory & Periodicity PPT

The ATOM
Discovery of the Electron
In 1897, J.J. Thomson used a cathode ray tube
to deduce the presence of a negatively charged
particle.
Cathode ray tubes pass electricity through a gas
that is contained at a very low pressure.
Thomson’s Atomic Model
Thomson believed that the electrons were like plums
embedded in a positively charged “pudding,” thus it was
called the “plum pudding” model.
Rutherford’s Gold Foil Experiment
 Alpha particles are helium nuclei
 Particles were fired at a thin sheet of gold foil
 Particle hits on the detecting screen (film) are
recorded
The Great Niels Bohr
(1885 - 1962)
Spectroscopic analysis of the visible spectrum…
…produces all of the colors in a continuous spectrum
Spectroscopic analysis of the hydrogen
spectrum…
…produces a “bright line” spectrum
Electron transitions
involve jumps of
definite amounts of
energy.
This produces bands
of light with definite
wavelengths.
Types of electromagnetic radiation:
Electromagnetic radiation propagates through
space as a wave moving at the speed of
light.
c = 
C = speed of light, a constant (2.998 x 108 m/s)
 = frequency, in units of hertz (hz, sec-1)
 = wavelength, in meters
TRY PROBLEM 39
Prepare yourself to
^
C
The energy (E ) of electromagnetic
radiation is directly proportional to the
frequency () of the radiation.
E = h
E = Energy, in units of Joules
h = Planck’s constant (6.626 x 10-34 J·s)
 = frequency, in units of hertz (hz, sec-1)
Long
Wavelength
=
Low Frequency
=
Low ENERGY
Short
Wavelength
=
High Frequency
=
High ENERGY
Wavelength Table
Relating Frequency, Wavelength
and Energy
c 
E  h
Common re-arrangements:
E
hc

hc

E
TRY PROBLEM 51
ANSWER IN NANOMETERS
Types of electromagnetic radiation:
Relating Frequency, Wavelength
and Energy
c 
E  h
Common re-arrangements:
E
hc

hc

E
WHICH FORM OF ELECTROMAGNETIC
RADIATION HAS THE LONGEST
WAVELENGTHS?
70%
icr
m
m
a
ow
...
ra
y
av
e
s
s
x-rays
9%
xra
ys
0%
ga
m
5.
4%
ia
infrared radiation
ra
d
4.
17%
re
d
radio waves
av
es
3.
in
fra
microwaves
w
2.
io
gamma rays
ra
d
1.
WHICH OF THE FOLLOWING FREQUENCIES
CORRESPONDS TO LIGHT WITH THE LONGEST
WAVELENGTH?
45%
1. 3.00 x 1013 s–1
2. 4.12 x 105 s–1
32%
14%
3. 8.50 x 1020 s–1
10
13
s–
. ..
4.1
2x
10
5s
8.5
–1
0x
10
20
s–
9.1
. ..
2x
10
12
s–
. ..
3.2
0x
10
9s
–1
5. 3.20 x 109 s–1
5%
0%
3.0
0x
4. 9.12 x 1012 s–1
5%
PLANCK’S PRACTICE PROBLEMS
A photon of light produced by a surgical laser
has an energy of 3.027 x 10-22 kJ. Calculate the
frequency and the wavelength of the photon.
Frequency = 4.57x1014 hz, 456 terahertz
Wavelength = 6.56x10-7 m, 656 nm
Work on your HW
The Great Niels Bohr
(1885 - 1962)
Spectroscopic analysis of the visible spectrum…
…produces all of the colors in a continuous spectrum
Spectroscopic analysis of the hydrogen
spectrum…
…produces a “bright line” spectrum
Electron transitions
involve jumps of
definite amounts of
energy.
This produces bands
of light with definite
wavelengths.
Schrodinger Wave Equation

d
h

V 
8  m dx
2
2
2
2
 E
Equation for probability of a
single electron being found
along a single axis (x-axis)
Erwin Schrodinger
Heisenberg Uncertainty Principle
“One cannot simultaneously
determine both the position
and momentum of an electron.”
You can find out where the
electron is, but not where it
is going.
Werner
Heisenberg
OR…
You can find out where the
electron is going, but not
where it is!
Quantum Numbers
Each electron in an atom has a unique
set of 4 quantum numbers which describe
it.
 Principal quantum number
(n)
 Angular momentum quantum number (l)
 Magnetic quantum number (m)
 Spin quantum number
(s)
Principal Quantum Number
Generally symbolized by n, it denotes the shell
(energy level) in which the electron is located.
The principal quantum number (n) cannot be
zero.
 n must be 1, 2, 3, etc.
Number of electrons
that can fit in a shell:
2n2
Angular Momentum Quantum Number
The angular momentum quantum number, generally
symbolized by l, denotes the orbital (subshell) in
which the electron is located.
The angular momentum quantum number (l ) can be any integer
between 0 and n - 1.
l =3
f
An orbital is a region within an atom where there
is a probability of finding an electron. This is a
probability diagram for the s orbital in the first
energy level…
Orbital shapes are defined as the surface that
contains 90% of the total electron probability.
Magnetic Quantum Number
The magnetic quantum number, generally
symbolized by m, denotes the orientation of the
electron’s orbital with respect to the three axes in
space. The magnetic quantum number (ml) can be any integer
between -l and +l.
Pauli Exclusion Principle
No two electrons in an atom
can have the same four
quantum numbers.
Wolfgang
Pauli
Spin Quantum Number
Spin quantum number denotes the behavior
(direction of spin) of an electron within a
magnetic field.
Possibilities for electron spin:
1

2
1

2
Assigning the Numbers
 The three quantum numbers (n, l, and m) are
integers.
 The principal quantum number (n) cannot be
zero.
 n must be 1, 2, 3, etc.
 The angular momentum quantum number (l )
can be any integer between 0 and n - 1.
 For n = 3, l can be either 0, 1, or 2.
 The magnetic quantum number (ml) can be any
integer between -l and +l.
 For l = 2, m can be either -2, -1, 0, +1, +2.
Principle, angular momentum, and magnetic
quantum numbers: n, l, and ml
Aufbau
Orbital filling table
Yet Another Way to Look at Ionization Energ
Element
Lithium
Configuration
notation
1s22s1
[He]2s1
____
1s
Beryllium
____
____
2p
____
____
2s
____
____
2p
____
[He]2s2p2
____
2s
____
____
2p
____
1s22s2p3
[He]2s2p3
____
2s
____
____
2p
____
1s22s2p4
[He]2s2p4
____
2s
____
____
2p
____
1s22s2p5
[He]2s2p5
____
1s
Neon
____
2s
1s22s2p2
____
1s
Fluorine
____
[He]2s2p1
____
1s
Oxygen
____
2p
1s22s2p1
____
1s
Nitrogen
____
[He]2s2
____
1s
Carbon
____
2s
1s22s2
____
1s
Boron
Noble gas
notation
Orbital notation
____
2s
____
____
2p
____
1s22s2p6
[He]2s2p6
____
1s
____
2s
____
____
2p
____
Periodicity
ATOMIC SIZE
}
Radius
Atomic Radius = half the distance between two
nuclei of a diatomic molecule.
TRENDS IN ATOMIC SIZE
• Influenced by three factors.
• Energy Level
• Higher energy level is further away.
• Charge on nucleus
• More charge pulls electrons in closer.
• Shielding
• Layers of electrons shield from nuclear pull.
SHIELDING
• The electron on the
outside energy level
has to look through all
the other energy levels
to see the nucleus
SHIELDING
• The electron on the
outside energy level has
to look through all the
other energy levels to
see the nucleus.
• A second electron has
the same shielding.
GROUP
TRENDS
• As we go down a
group
H
Li
Na
• Each atom has
another energy
level,
K
• So the atoms get
bigger.
Rb
PERIODIC TRENDS
•
•
•
•
As you go across a period the radius gets smaller.
Same energy level.
More nuclear charge.
Outermost electrons are closer.
Na
Mg
Al
Si
P
S Cl Ar
Table
of
Atomi
c
Radii
IONIC SIZE
• Cations form by losing electrons.
• Cations are smaller that the atom they come from.
• Metals form cations.
• Cations of representative elements have noble gas
configuration.
IONIC SIZE
• Anions form by gaining electrons.
• Anions are bigger that the atom they come from.
• Nonmetals form anions.
• Anions of representative elements have noble gas
configuration.
Rb
K
OVERALL
Atomic Radius (nm)
Na
Li
Kr
Ar
H
Ne
10
Atomic Number
Put the following in order of
Decreasing atomic radius:
a) Cl,Ar,K
b) O, O-, O2c) Co, Rh, Ni
Now put them in order of Decreasing
ionization energy:
IONIZATION
ENERGY
• The amount of energy required to completely
remove an electron from a gaseous atom.
• Removing one electron makes a +1 ion.
• The energy required is called the first ionization
energy.
IONIZATION ENERGY
• The second ionization energy is the
energy required to remove the second
electron.
• Always greater than first IE.
• The third IE is the energy required to
remove a third electron.
DO PROBLEM 110
Symbol First
H
He
Li
Be
B
C
N
O
F
Ne
1312
2731
520
900
800
1086
1402
1314
1681
2080
Second
Third
5247
7297
1757
2430
2352
2857
3391
3375
3963
11810
14840
3569
4619
4577
5301
6045
6276
WHAT DETERMINES IE
• The greater the nuclear charge the greater IE.
• Distance from nucleus increases IE
• Filled and half filled orbitals have lower energy, so
achieving them is easier, lower IE.
• Shielding
GROUP TRENDS
• As you go down a group first IE
decreases because
• The electron is further away.
• More shielding.
PERIODIC TRENDS
• All the atoms in the same period have the same
energy level.
• Same shielding.
• Increasing nuclear charge
• So IE generally increases from left to right.
• Exceptions at full and 1/2 fill orbitals.
Electron Affinity - the energy change
associated with the addition of an electron
 Affinity tends to increase across a period
 Affinity tends to decrease as you go down
in a group
Electrons farther from the nucleus
experience less nuclear attraction
Some irregularities due to repulsive
forces in the relatively small p orbitals
P ELECTRONSPECTROSCOPY
HOTO
PES
• method that provides information on all the occupied
energy levels of an atom (that is, the ionization
energies of all electrons in the atom) is known as
photoelectron spectroscopy; this method uses a
photon (a packet of light energy) to knock an electron
out of an atom.
PHOTOELECTRON SPECTRUM
The photoelectron spectrum is a plot of the number of electrons emitted versus their
kinetic energy. In the diagram below, the “X” axis is labeled high to low energies so
that you think about the XY intersect as being the nucleus.


http://www.chem.arizona.edu/chemt/Flash/photoelectron.html
2p
6-
2- 1s
1-
2s
3p
3s
4s
Orbital names s, p, d,
and f stand for names
given to groups of lines
in the spectra of the
alkali metals. Early
chemists called the line
groups sharp, principal,
diffuse, and
fundamental.
Interpretations from the data:
1. There are no values on the y axis in the tables above. Using the Periodic Table
and Table 1, put numbers on the y axis.
2. Label each peak on the graphs above with s, p, d, or f to indicate the suborbital
they represent..
3. What is the total number of electrons in a neutral potassium atom?
PES QUESTION
• If a certain element being studied by an X-ray PES displays an emission
spectrum with 5 distinct kinetic energies. What are all the possible elements
that could produce this spectrum?
• Determine the orbitals that the spectral lines are originating from and then
determine the elements that have electrons in only these orbitals.
DO PROBLEM 117
DO PROBLEM 121