ATOMIC STRUCTURE AND
PERIODICITY PART 2
PERIODIC TRENDS
Atomic Radii
Ionic Radii
Electronegativity
Ionization Energy
Electron Affinity
ATOMIC RADIUS
2r
Definition: Half of the distance between nuclei in
covalently bonded diatomic molecule.
Radius decreases across a period
• Increased effective nuclear charge due to decreased
shielding
Radius increases down a group
• Each row on the periodic table adds a “shell” or
energy level to the atom
IONIZATION ENERGY
Definition: the energy required to remove an electron
from an atom
**Increases for successive electrons taken from the same atom.
(First Ionization Energy is lower than the second…and that lower
than the third…etc)
Tends to increase across a period (general pattern-valence e-)
•
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
Tends to decrease down a group
•
Outer electrons are farther from the nucleus and easier to
remove
IONIZATION ENERGY AND
ORBITAL NOTATION
Phosphorus vs. Sulfur
Potassium 1st Ionization vs. 2nd
ELECTRON AFFINITY
Definition: the energy change associated with the
addition of an electron
Affinity tends to increase across a period
Affinity tends to increase up in a group
• Electrons farther from the nucleus experience
less nuclear attraction
• Some irregularities due to repulsive forces in the
relatively small “p” orbitals
ELECTRONEGATIVITY
Definition: A measure of the ability of an atom in a
chemical compound to attract electrons from another
atom.
Electronegativity tends to increase across a period
• As the radius decreases, electrons get closer to the
bonding atom’s nucleus
Electronegativity tends to increase up a group or
remain the same.
• As radius increases, electrons are farther from the
bonding atom’s nucleus
IONIC RADII
Cations
• Positively charged ions formed when an atom
loses one or more electrons
• SMALLER that the corresponding atom
Anions
• Negatively charged ions formed when an atom
gains one or more electrons
• LARGER than the corresponding atom
ANALYZING PERIODIC TABLE
TRENDS WITH PEERS
Explain why atomic radius increases going down a
group and right to left in a period.
Rank the following from largest to smallest.
Explain why electronegativity, ionization energy, and
electron affinity increase from left to right and from
bottom to top.
Rank the following from largest to smallest.
SPECTROSCOPY
Photoelectron Spectroscopy (PES)
• Provides data for ionization energy trends and
applications
Mass Spectrometry
• Provides atomic/molar mass data as it ionizes
PHOTOELECTRON SPECTROSCOPY (PES)
Ephoton = hv
Atom
Monochromatic
Beam of X-Rays
IEelectron = Ephoton - KE
KE = mv2
2
e-
PHOTOELECTRON SPECTRUM
Relative Intensity = 2
Each peak is relative to the others. This indicates
the relative number of electrons. If the peak is
twice as big, there are twice as many electrons.
Relative Intensity = 1
20 MJ/mol
10 MJ/mol
0 MJ/mol
PHOTOELECTRON SPECTRUM
Valence
19.3 MJ/mol
1.36 MJ/mol
RI = 2
RI = 2
Gap is due to increased energy of the orbital
(decreased amount of energy to remove the
electron)
20 MJ/mol
10 MJ/mol
0.80 MJ/mol
RI = 1
0 MJ/mol
PHOTOELECTRON SPECTRUM
Boron (Z=5)
19.3 MJ/mol
RI = 2
Analysis:
1) Valence has 2 values:
2) RI is 2 to 1 in valence:
3) Closest core has RI 2 not 6:
4) s2s2p1 must be 1s22s22p1
RI = 2
0.80 MJ/mol
RI = 1
2s2
1s2
20 MJ/mol
1.36 MJ/mol
10 MJ/mol
Inner orbitals require
the most energy
2p1
0 MJ/mol
Valence orbitals require the
least energy
PHOTOELECTRON SPECTRUM
Depending on the size of the table, 1s may be intentionally cut
out of view because it’s too far away and makes the graph too
long
Remember IE is about REMOVING electrons, which means they
are removed from the OUTSIDE to the INSIDE, and NOT in
reverse order of energy! For example, 4s is removed BEFORE
3d.
PHOTOELECTRON SPECTRUM
2p6
3.67 MJ/mol
1s2
2s2
104 MJ/mol
Sodium (Z=11)
3s1
6.84 MJ/mol
0.50 MJ/mol
{}
8 MJ/mol
4 MJ/mol
0 MJ/mol
Online PES Resources
http://www.chem.arizona.edu/chemt/Flash/photoelectron.
html
https://www.youtube.com/watch?v=NRIqXeY1R_I
https://www.youtube.com/watch?v=vANbxozsRSA
From the AP Sample Questions…
From the AP Sample Questions…
Which peaks in the photoelectron spectrum are representative of the
binding energy of p orbital electrons?
a. C only
c. C and E
b. D only
d. B, C and D
Mass Spectrometry
• Mass spectrometry gives the mass to charge
ratio
• Like PES, the relative size of the peaks
indicates the relative number of particles
• Separates isotopes according to mass
• Used to find relative abundance and
atomic/molar mass of unknown samples
Mass Spectrometry
From the AP Sample Questions…
The elements I and Te have similar average atomic masses. A sample that
was believed to be a mixture of I and Te was run through a mass
spectrometer, resulting in the data above. All of the following statements are
true. Which one would be the best basis for concluding that the sample was
pure Te?
From the AP Sample Questions…
a. Te forms ions with a -2 charge, whereas I forms ions with a -1
charge.
b. Te is more abundant that I in the universe.
c. I consists of only one naturally occurring isotope with 74 neutrons,
whereas Te has more than one isotope.
d. I has a higher first ionization energy than Te does.
Based on the mass spectrum of atom Y, which of the following statements is false?
a. peak A and peak D come from atoms that have the same number of electrons
b. there are seven isotopes of atom Y
c. peak C comes from the most abundant isotope of atom Y
d. peak D comes from an atom with 4 more protons than the atom that gave peak B
PREPARATION OF A STANDARD
SOLUTION
A chemist whishes to prepare 1.00L of a 0.200 M
sodium hydroxide solution. Describe the steps,
with calculations, necessary to complete this task
starting with solid sodium hydroxide and distilled
water.
DILUTION OF SOLUTIONSM1V1 = M2V2
(a) A
Measuring
Pipet
(b) A
Volumetric
(transfer)
Pipet
You’ve been asked to prepare 150 ml of a 0.035M
solution of sodium hydroxide from the 0.200M stock
sodium hydroxide solution prepared earlier. Detail
the steps necessary to complete this task.
BEER- LAMBERT LAW
Relates the amount of light being
absorbed to the concentration of
the substance absorbing the light
A=abc
A = measured absorbance
a = molar absorptivity constant (a
characteristic of the substance
being monitored).
b = path length through which the
light must pass.
c = Molar concentration of the
absorbing substance.
BEER’S LAW SAMPLE PROBLEMS
1. A solution with a concentration of 0.14M is measured to have an
absorbance of 0.43. Another solution of the same chemical is
measured under the same conditions and has an absorbance of 0.37.
What is its concentration?
2. The following data were obtained for 1.00 cm samples of a
particular chemical. What is the concentration of a 1.00 cm
sample that has an absorbance of 0.60?
Conc.
Abs.
(M)
3. The absorptivity of a particular
chemical is 1.5/M·cm. What is the
concentration of a solution made from
this chemical if a 2.0 cm sample has an
absorbance of 1.20?
0.50
0.69
0.40
0.55
0.30
0.41
0.20
0.27
BEER’S LAW SAMPLE
PROBLEMS
4. Using the data from the graphing example in question #2, what are
the concentrations of solutions with absorbances of 0.20, 0.33, and
0.47?
5. A solution is prepared to be 0.200M. A sample of this solution 1.00
cm thick has an absorbance of 0.125 measured at 470nm and an
absorbance of 0.070 measured at 550nm. Calculate the concentrations
of the following solutions:
Sample
Absorbance
Wavelength
Path length
1
0.055
470nm
1.00cm
2
0.155
470nm
1.00cm
3
0.120
550nm
1.00cm
4
0.048
550nm
5.00cm
GATORADE
LAB/INVESTIGATION
What is the relationship between the concentration of a
solution and the amount of transmitted light through the
solution?
Video Spectrophotometer
See Pre-lab and Report Sheet for support.
**Dilution calculations MUST be done prior to data
collection!!** (Due Monday!) –complete first 3 columns in
data table prior to entering lab.
LAB PARTNERS AND DILUTION ASSIGNMENTS
2ND BLOCK
Dilution Assignments (mL of stock/ mL of water)
Group 1: Jackson and Kenny
• 10mL/0mL; 6mL/4mL
• 9mL/1mL; 3mL/7mL
Group 2: Garrett and Nelson
• 5mL/5mL; 0mL/10mL
• 8mL/2mL; 1mL/9mL
Group 3: Ashley and Taylor
• 2mL/8mL; 4mL/6mL,
• 0mL/10mL, 7mL/3mL
Will share class data for plots.
UNIT 3 REVIEW
Now available on the blog!! (Practice Tab)
Begin working through.
BRING QUESTIONS TOMORROW!!!!