1. Launch: 9/24
 Grab your binder and immediately take a seat
 Place Textbook HW on desk
5. Which of the following atoms has the largest
atomic radius?
a. oxygen (O)
b. phosphorus (P)
c. sulfur (S)
d. chlorine (Cl)

2. What is the trend for
ionization energy?
Mr. Heffner
9/24/09

3. Review: Atomic Radius
Decreases
Increases

4. IV. Ionization Energy
A. What is ionization energy?
1. The energy it takes to remove an electron from an atom
2. Atoms can have multiple ionization energies
i. First ionization energy – the energy it takes to remove the
first electron
ii. Second ionization energy – the energy it takes to remove the
second electron
iii. Third ionization energy – the energy it takes to remove the
third electron

5. IV. Ionization Energy
B. What is the trend for first ionization energy?
1. Ionization energy increases across a period (LR)
i. As the number of protons increases, atomic radius
decreases
ii. It is harder to take an electron off a small atom, so
ionization energy increases

6. Chihuahua Story
 I am a dog walker and everyday I walk 8
 The stronger I am, the closer I can pull them
towards me
 The closer they are to me, the harder they are to
steal!

7. IV. Ionization Energy
B. What is the trend for first ionization energy?
2. Ionization energy decreases down a group
(TopBottom)
i. As the number of electrons increases, atomic radius
increases
ii. It is easier to take an electrons off a large atom, so
ionization energy decreases

8. Chihuahua Story
 I am a dog walker and now I have 9
 I can’t fit any more around me, need a longer leash
 It is easier to steal one when it is farther away!

9. IV. Ionization Energy
Increases
Decreases

10. IV. Ionization Energy
A. What is the trend for second & third ionization
energy?
1. The trend is the same as first ionization energy
2. However, the amount of energy is always larger than
first
i. After one electron is removed, the protons pull the
remaining electrons closer to the nucleus making the atom
smaller
ii. It is harder to take an electron off a small atom, so second
ionization energy is larger than first

11. Practice Questions
1. What is ionization energy?
2. Describe the trend for ionization energy. How does it
compare to atomic radius?
3. Which has a larger ionization energy, P or S; F or Cl; Li
or Cs; Pt or Ni; Fr or F; Se or O?
4. Which element in group 2 has the largest ionization
energy? The smallest?
5. Magnesium has a first ionization energy of 737.7 kJ/
mol and second ionization energy of 1450.7 kJ/mol.
Use what you know to explain this phenomenon in at
least two complete sentences.

12. Homework
 Textbook Problems:
 Pg. 141 Section Review: #1, 5, 11, 12, 13
 Finish Practice Problems
 Start reviewing for Monday’s Unit #2 Exam!
 lpschem.wordpress.com

13. Exit Slip
1. Ionization energy is the
a. number of stable ions formed by an atom.
b. number of protons and neutrons in an atom.
c. energy it takes to remove an electron from an atom.
d. distance from the nucleus to the valence ring.

14. Exit Slip
2. In general, how does ionization energy vary
throughout the periodic table?
a. it decreases across a period from left to right, and
decreases down a group from top to bottom
b. it increases across a period from left to right, and
increases down a group from top to bottom
c. it increases across a period from left to right, and
decreases down a group from top to bottom
d. It decreases across a period from left to right, and
increases down a group from top to bottom

15. Exit Slip
3. Which of the following correctly describes the
relationship between first and second ionization
energy?
a. First ionization energy is always larger than second
b. Second ionization energy is always larger than first
c. First ionization energy describes positively-charged
ions, while second ionization energy describes
negatively-charge ions
d. First ionization energy describes negatively-charged
ions, while second ionization energy describes
positively-charge ions

16. Exit Slip
4. Which of the following atoms has the smallest first
ionization energy?
a. lithium (Li)
b. beryllium (Be)
c. sodium (Na)
d. magnesium (Mg)

17. 5. The chart above shows the relationship between
the first ionization energy and the increase in
atomic number. The letter on the chart that
represents the noble gases is:
a. W
b. X
c. Y
d. Z