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:

• Why is there a huge jump seen between IE4 and IE5?

First Ionization Energy (IE1) 786 kJ/mol

IE2 1577 kJ/mol

IE3 3232 kJ/mol

IE4 4356 kJ/mol

IE5 16,091 kJ/mol

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+ + e-

F + 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