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Catalyst
1. What are the trends for ionization energy? Why do these
trends exist?
2. As you go across a period, do elements get better or worse at
attracting electrons? Justify your response.
3. As you go down a group, do elements get better or worse at
attracting electrons? Justify your response.
Today’s Learning Targets
• 1.9 – I can define and calculate the effective nuclear charge for an
atom and explain how this impacts observed periodic trends.
• 1.11 – I can define ionization energy and explain how it relates to
the effective nuclear charge. Furthermore, I can explain how this
trend changes as you move throughout the Periodic Table and
relate it to the elements quantum electron configuration.
• 1.12 – I can define electron affinity and explain how it relates to the
effective nuclear charge. Furthermore, I can explain how this trend
changes as you move throughout the Periodic Table and relate it to
the elements quantum electron configuration.
Ionization Energy
• Ionization Energy – The minimum energy needed to
remove an electron from an element.
Elements Can Have Multiple
Ionization Energies
• The first ionization energy is the energy to remove 1
electron from a neutral atom:
Na  Na+ + 1 e• The second ionization energy is the energy needed to
remove the 2nd electron from a charged atom:
Na+  Na+2 + 1 e• 2nd IE > 1st IE
• The IE increases as you remove more electrons
because you are pulling an electron from a more
positive atom.
Justify – TPS
• Examine the ionization energies for silicon below:
First Ionization Energy (IE1)
786 kJ/mol
IE2
1577 kJ/mol
IE3
3232 kJ/mol
IE4
4356 kJ/mol
IE5
16,091 kJ/mol
• Why is there a huge jump seen between IE4 and IE5?
Periodic Trend for IE
• IE increases across a period because there is a higher
Zef, so the nucleus holds onto the electron more
tightly
• IE decreases down a group because there is a lower
Zef due to the fact that the electrons are further
away from the nucleus.
Class Example
• Which of the colored elements on the Periodic Table below
will have the highest second ionization energy?
Table Talk
• The first ionization energy for nitrogen is 1402 kJ/mol. The
first ionization for oxygen is 1314 kJ/mol. Oxygen is further to
the right of nitrogen. Why does nitrogen have a higher first
ionization energy?
Justify – TPS
• Using electron configurations to defend your answer,
explain which of the following processes is more
favorable for fluorine:
F  F + + eF + e-  F-
Electron Affinity
• The opposite of ionization energy is electron affinity.
• This is the energy required to add an electron to an atom
• Measures the attraction for the nucleus to the newly
added electron
• The greater the attraction between the atom and the
added electron, the more negative the electron affinity
value.
• E.g. Chlorine = -349 kJ/mol and Sodium = -53 kJ/mol
Table Talk
• Do you think neon will have a higher or lower
electron affinity than fluorine? You must justify your
response with evidence for full credit.
Trend for Electron Affinity
• Elements that only need one (or two) electron to fill or “half”
fill a subshell will have much higher electron affinities than
element that already have a filled subshell.
• Therefore, the only way to predict electron affinities is by
examining the element’s electron configuration.
• Electron affinities do not vary much as we go down a group
Summarize
White Board Races
Question 1
• The electron affinities of five elements are given below:
1. Define the term “electron affinity” of an atom.
2. For the elements listed above, explain the observed trend
with the increase in atomic number. Account for the
discontinuity that occurs at phosphorus
Question 2
2. Use the details of atomic theory to explain each
of the following experimental observations.
a. Within a family such as the alkali metals,
the ionic radius increase as the atomic
number increases.
Question 3
3. Use the details of atomic theory to explain each
of the following experimental observations:
b. The radius of the chlorine atom is smaller
than the radius of the chloride ion, Cl-.
(Radii:
Cl atom = 0.99 Å; Cl- ion = 1.81 Å)
Question 4
4. Use the details of atomic theory to explain each
of the following experimental observations.
c. The first ionization energy of aluminum is
lower than the first ionization energy of
magnesium (First ionization energies: 12Mg =
7.6 ev; 13Al = 6.0 ev)
Question 5
5. Use the details of atomic theory to explain each
of the following experimental observations.
d. For magnesium, the difference between
the second and third ionization energies is
much larger than the difference between the
first and second ionization energies.
(Ionization energies for Mg: 1st = 7.6 ev; 2nd =
14 ev; 3rd = 80 ev)
Paper in Water
Lab 3: Chromatography and
Sharpies
• Take down the following notes in your lab manual
• These notes will help with your formal lab report on this lab
Lab Worktime
Closing Time
• Finish Chapter 7 and all corresponding problems to stay
on task.
• Lab report on Lab 3: Chromatography and Sharpies due
September 4th