Download APC-Ch.7-Atomic Structure and Periodicity

Atomic Structure and Periodicity
Chapter 7
Unit 4 - Atomic Structure, Periodicitiy, and Bonding
AP Chemistry
Electromagnetic Radiation
Classification of Electromagnetic Radiation
Wavelength decreases →
Frequency decreases →
Energy decreases →
8
Speed is constant = 3.00 x 10 m/s
Electromagnetic Radiation
Properties of Electromagnetic Waves
Wavelength (λ)
distance between two consecutive crests or troughs in a wave
measured in meters
Frequency (v)
number of waves that pass a given point per second
measured in hertz (1/sec)
Speed (c)
measured in meters per second (m/s)
When one physicist asked another, “What’s new?”, the typical response is “C over lambda”.
Electromagnetic Radiation
Frequency and Wavelength
λv = c
The Nature of Matter
Max Planck
Quantum Theory
Energy is gained or lost in whole number multiples of the quantity hv
ΔE = nhv
v = frequency
-34
h = Planck’s constant = 6.626 x 10
Energy is transferred to matter in packets of energy called
quantum.
The Nature of Matter
Max Planck
Sample Problem A
The yellow light given off by a sodium vapor lamp has a wavelength of 589
nm.
a) What is the frequency of this radiation?
b)Calculate the energy of one photon of yellow light.
The Nature of Matter
Albert Einstien
Electromagnetic radiation is a stream of particles called photons.
hc
E = hv =
λ
Energy and mass are inter-related.
E = mc
2
The Nature of Matter
Louis de Broglie
Light travels through space as a wave.
Light transmits energy as particles.
Particles have wavelength, exhibited by diffraction
patterns.
h
λ=
mv
Large particles have very short wavelengths.
All matter exhibits both particle and wave properties.
The Nature of Matter
Louis de Broglie
Sample Problem B
What is the wavelength of an electron moving with a speed of 5.87 x
-28
m/s? (mass of electron = 9.11 x 10 g)
6
10
The Atomic Spectrum of Hydrogen
The Atomic Spectrum of Hydrogen
Continuous spectra - contains all wavelengths of light
Bright line spectra
Excited electrons in an atom return to lower energy states
Energy is emitted in the form of a photon of definited wavelength
Definite change in energy corresponds to:
Definite frequency
Definite wavelength
hc
ΔE = hv =
λ
Only certain energies are possible within any atom
The Atomic Spectrum of Hydrogen
Bright Line Spectra
The Atomic Spectrum of Hydrogen
Energy Transitions for Hydrogen
The Bohr Model
Niels Bohr
The electron moves around the nucleus only in certain allowed
circular orbits.
Bright line spectra confirms that only
certain energies exist in the atom and the
atom emits photons with definite
wavelengths when the electron returns to
the lower energy state.
The Bohr Model
Shortcomings of the Bohr Model
Does not work for atoms other than hydrogen
Electrons do not move in circular orbits.
The Quantum Mechanical Model of the Atom
Quantum Mechanical Model
The electron as a standing wave
Do not propagate through space
Fixed at both ends
Only certain size orbits can contain whole numbers of half wavelengths
Fits the quanta observation
Orbitals
are NOT circular
ARE areas of probability for locating
The Quantum Mechanical Model of the Atom
Heisenberg Uncertainty Principle
The more accurately we know the position of any particle, the less
accurately we can know its momentum, and vice versa
This is apparently a true story. It took place just outside of
Munich, Germany. Heisenberg went for a drive and got
stopped by a traffic cop. The cop asked, “Do you know how
fast you were going?” Heisenberg replied, “No, but I know
where I am.”
Q: Why are quantum physicists so poor at sex?
A: Because when they find the position, they can’t find the
momenutum, and when they find the momentum, they can’t
find the position.
Quantum Numbers
Quantum Numbers
Principal Quantum Number (n)
Integral Values: 1, 2, 3...
Indicates probable distance from the nucleus
Higher numbers = greater distance
Greater distance = less tightly bound = higher energy
Quantum Numbers
Quantum Numbers
Angular Momentum Quantum Number (l)
Integral values from 0 to n-1
Indicates shapes of atomic orbitals
Angular Momentum #’s and Atomic Orbitals
Value of
l
0
1
2
3
4
Letter
used
s
p
d
f
g
Quantum Numbers
Quantum Numbers
Magnetic Quantum Number (ml)
Integral values from l to -l, including zero
relates to the orientation of the orbital in space relative to the other
orbitals
Spin Quantum Number (ms)
Orbitals can only hold 2 electrons
they must have opposite spins
+1/2 or -1/2
Pauli Exclusion Principle - in a given atom, no two electrons can have
the same set of four quantum numbers.
Quantum Numbers
Quantum Numbers
Sample Problem C
For n = 4, what are the possible values of l?
For l = 2, what are the possible values of ml?
Quantum Numbers
Orbital Shapes and Energies
Size of Orbitals
defined as the surface that contains 90% of the total electron probability
Orbitals of the same shape grow larger as n increases
s Orbital
spherical
p Orbital
two lobes each, dumbbell
occurs in levels n = 2 and greater
Quantum Numbers
Orbital Shapes and Energies
d Orbital
clover shape
occus in levels n = 3 and greater
Quantum Numbers
Orbital Shapes and Energies
f Orbital
flower shape
occus in levels n = 4 and greater
not involved in bonding in most compounds
Quantum Numbers
Orbital Shapes and Energies
All orbitals with the same value of n have the same energy
Lowest energy state = ground state
When the atom absorbs energy, electrons may move to higher energy
orbitals or an excited state.
An electron sitting in a prison asked a second electron cellmate, “What are you in for?”
To which the latter replied, “For attempting a forbidden transition.”
Polyelectronic Atoms
Polyelectronic Atoms
Internal Atomic Energies
Kinetic energy - moving electrons
Potential energy of attraction between nucleus and electrons
Potential energy of repulsion between electrons
Screening or Shielding
Electrons are attracted to the nucleus
Electrons are repulsed by other electrons
Electrons would be bound more tightly if other electrons weren’t there
Electron Configuration
Rules and Principles
Aufbau Principle
As protons are added one by one to the nucleus to build up elements,
electrons are similarly added to these hydrogen-like orbitals.
Hund’s Rule
The lowest energy configuration for an atom is the one having the
maximum number of unpaired electrons allowed by the Pauli exclusion
principle.
You have to be single before you can have your “Hunny”
Electron Configuration
Electron Configuration
Aufbau Principle
As protons are added one by one to the nucleus to build up elements,
electrons are similarly added to these hydrogen-like orbitals.
Q: What do you call a joke that is based on cobalt, radon, and yttrium?
A: CoRnY
Electron Configuration
Electron Configuration
Sample Problem D
Draw the orbital diagram for the electron configuration of oxygen, atomic
number 8.
How many unpaired electrons does an oxygen atom possess?
Electron Configuration
Electron Configuration
Sample Problem E
Draw the orbital diagram for the electron configuration of phosphorus,
atomic number 15.
How many unpaired electrons does an phosphorus atom possess?
Electron Configuration
AP Exam Sample
Sample Problem F
Write the ground state electron configuration for an arsenic atom, showing
the number of electrons in each subshell.
a.
b.Give one permissible set of four quantum numbers for each of the
outermost electrons in a single As atom when it is in its ground state.
c. Is an isolated arsenic atom in the ground state paramagnetic or
diamagnetic? Explain briefly.
d.Explain how the electron configuration of the arsenic atom in the ground
state is consistent with the existence of the following known compounds:
Na3As, AsCl3, and AsF5.
Daily Objectives
Chemistry II Honors
Today, I will be able to
describe the trends of elemental properties in terms of the periodic
table.
•
LO 1.6, 1.7, 1.8, 1.9, 1.10
Which element is...?
1.Half of a dimeNickel
2.The Lone Ranger’s horse Silver
3.Not fat Tin
4.Watered down gin
Hydrogen
5.A police officer Copper
6.What I do when I’m hungry Iodine
7.What torpedoed ships do Zinc
8.Male member of the Ganese tribe Manganese
9.What he did with a bucking horse Rhodium
10.What should be done with an ailing man Helium/Curium/Barium
The Periodic Table
Periodic Table Vocabulary
Valence Electrons
Outermost principle quantum level of an atom
Elements in the same group (column) have the same valence electron
configuration
Periodic Trends
Ionization Energy
Ionization energy is the energy required to remove an electron from an
atom.
increases for successive electrons
Increases across a period
Electrons in the same quantum level do not shield as effectively as electrons in inner
levels
Irregularities at half filled and filled sublevels due to extra repulsion of electrons paired
in orbitals, making them easier to remove
Decreases with increasing atomic number within a group
Electrons further from the nucleus are easier to remove
Periodic Trends
Ionization Energy
Sample Problem G
Referring to a periodic table, arrange the following atoms in order of
increasing first ionization energy: Ne, Na, P, Ar, K
Periodic Trends
Ionization Energy
Sample Problem H
Which has the lowest first ionization energy, B, Al, C, or Si? Which has the
highest?
Periodic Trends
Electron Affinity
Electron affinity is the energy change associated with the addition of an
electron.
increases across a period
decreases down a group
Electrons farther from the nucleus experience less nuclear attraction
Some irregularities due to repulsive forces in the relatively small p orbitals
Periodic Trends
Electron Affinity
Sample Problem I
The electron affinity of lithium is a negative value, where as the electron
affinity of beryllium is a positive value. Use electron configuration to account
for this observation.
Periodic Trends
Atomic Radius
Atomic radius is half of the distance between radii in a covalently
bonded diatomic molecule
•
Trends
Decreases across a period
increased effective nuclear charge due to decreased shielding
Increases down a group
addition of principle quantum levels
Periodic Trends
Atomic Radius
Sample Problem J
Referring to a periodic table, arrange the following atoms in order of
increasing size: P, S, As, Se.
Periodic Trends
Ionic Radius
Anions are larger than parent atoms.
Cations are smaller than parent atoms.
Ion size increases within a family
Isoelectronic ions
Ions with the same number of electrons
Size decreases as the nuclear charge increases
Periodic Trends
Ionic Radius
Sample Problem K
+1
-1
+2
-2
Arrange the ions, K , Cl , Ca , and S , in order of decreasing size.
Photoelectron Spectroscopy
Photoelectron Spectroscopy
Photoelectron Spectroscopy (PES) is a technique that is used to gather
information about the electrons in an atom
An atom is bombarded with photons. Some of the photons are absorbed
and electrons are emitted. the energy is analyzed. Since we can know
the energy of the photons, and we know that energy is conserved we
know that the difference in energy between the photons sent into th
eatom and the energy of the electrons emitted will be the potential energy
of the electrons when they are attached to the atom. Remember that the
potential energy of the electron in the atom is the work needed to remove
the electron from the atom.
Energy of emitted electron = energy of photon - work needed to remove
electron from atom
Photoelectron Spectroscopy
Photoelectron Spectroscopy
How do scientists find ionization energy?
PES can tell what about an atom?
PES provides evidence for ____.
How does PES work?
The size of a peak on a graph means ____.
Electrons are held most tightly ____.
Photoelectron Spectroscopy
Hydrogen
The whole number is the integration of the number of electrons in the
spectrum. The decimal number is the work needed to remove the electron
from the atom in MJ/mol.
Photoelectron Spectroscopy
Helium
Helium has an integration of 2 and the energy is higher than hydrogen. This
is because He has 2 electrons and H has 1. Also, H and He have the same
level of shielding (none) while He has 2 protons and H has 1. That makes it
harder to remove the electrons from He than from H.
Photoelectron Spectroscopy
Lithium
Lithium has two sets of electrons. 1 electron has lower energy, the 2 have
higher energy.
On the PES spectra, a high energy number means the electron is closer to
the nucleus, a low number means it is further from the nucleus.
Photoelectron Spectroscopy
Lithium
Lithium has two sets of electrons. 1 electron has lower energy, the 2 have
higher energy.
Note that the peak for an electron farther from the nucleus is closer to the
beginning of the graph while the peak for an electron closer to the
nucleus is farther from the beginning of the graph.
Think of the energy number on the graph as how hard it is to take the
electron away from the atom.
Photoelectron Spectroscopy
Boron
Boron has 2 electrons at 19.3 in the 1s. There are 2 electrons at 1.36 and
1 electron at 0.80. The 2 electrons are 2s and the 1 electron is 2p. Why
are they different? They are both in the same energy level (shell), so why do
they have different potential energies?
Photoelectron Spectroscopy
Boron
The reason the 2s and 2p orbitals have different energy is that s penetrates
better than p. An s orbital can overcome the effects of shielding better than
p. Remember that penetration ability is: s > p > d > f
Photoelectron Spectroscopy
Boron
So it is easier to remove an electron from the 2p orbital in B than from the
2s. That’s why the 2s are at 1.36 and the 2p is at 0.80.
Photoelectron Spectroscopy
Scandium
Photoelectron Spectroscopy
Scandium
The filling order has 3d after 4s
because 3d does not penetrate as
well as 4s.
However, in the spectrum for Sc we
can see that there are 2 electrons at
0.63 and 1 at 0.77.
This suggests that it is easier to remove the 4s than the 3d.
This is because n=3 shieds n=4. This raises the energy of 4s once 3d
starts to fill.
Photoelectron Spectroscopy
Photoelectron Spectroscopy
Sample Problem L
Identify the element shown above.
Photoelectron Spectroscopy
Photoelectron Spectroscopy
Sample Problem M
What happens to the 1s peak?
What is different about the graph
than the order you fill the electron
orbital diagrams?
Why is the 4s lower in energy than
3d?
Periodic Trends
AP Exam Sample
Sample Problem N
Account for each of the following in terms of principles of atom structure,
including number, properties, and arrangements of subatomic paricles.
a. The second ionization energy of sodium is about three times greater than
the second ionization energy of magnesium.
b.The difference between atomic radii of Na and K is relatively large
compared to the difference between the atomic radii of Rb and Cs.
Periodic Trends
AP Exam Sample
Sample Problem N
Account for each of the following in terms of principles of atom structure,
including number, properties, and arrangements of subatomic paricles.
c. A sample of nickel chloride is attracted into a magnetic field, whereas a
sample of solid zinc chloride is not.
d.Phosphorus forms the fluorides PF3 and PF5, whereas nitrogen forms only
NF3.
Periodic Trends
AP Exam Sample
Sample Problem O
Explain each of the following observations using principles of atomic
structure and/or bonding.
a. Potassium has a lower first ionization energy than lithium.
b.The ionic radius of
3N
is larger than that of
2O .
c. A calcium atom is larger than a zinc atom.
d.Boron has a lower first ionization energy than beryllium.