1. Trends of the Periodic Table Class #4
Cation Size, Anion Size,

2. That’s a lot to ponder, but it’s easy enough. Here goes…
The group trend for atomic size (atomic radius) for both metals and nonmetals is increasing, because each atom lower in the group has an additional orbital.
The more orbitals that you have, the bigger you are.
There are no measures for cations (or anions) so we will do this trend by examining the ions’ electron configurations and take into consideration the numbers of protons that they have. We’ll ponder the number of protons pulling on the number of electrons in each ion.
That’s a lot to ponder, but it’s easy enough Here goes…

3. Determine the group trends for cation size
Determine the group trends for cation size. Then the group trend for anion size as well.
Group 1
Atoms/cations
Group 1 cation electron configurations
Li+1
Na+1
K+1
Rb+1
Group 17
Atoms/anions
Group 17 anion electron configurations
F-1
Cl-1
Br-1
I-1
State the group trend for cation size in one sentence. Then, state the group trend for anion size in one MORE sentence.

4. WHY? Because going down any group (atom/ion) you always add orbitals.
Determine the group trends for cation size. Then the group trend for anion size as well.
Group 1
Atoms/cations
Group 1 cation electron configurations
Li+1 2
Na+1
2-8
K+1
2-8-8
Rb+1
Group 17
Atoms/anions
Group 17 anion electron configurations
F-1
2-8
Cl-1
2-8-8
Br-1
I-1
The group trend for cation size is increasing. The group trend for anion size is increasing.
WHY? Because going down any group (atom/ion) you always add orbitals.

5. For METALS… How does each atom compare to it’s cation?
Cations are smaller than their atoms always, because they have less orbitals.
For NONMETALS… How does each atom compare to it’s anion?
Anions are always slightly larger than their atoms, because they have more electrons repelling each other in the same number of orbitals.

6. Cation Electron configuration
Period Trend for Cation size…
Cations:
Na+1
Mg+2
Al+3
Cation Electron configuration
2-8
These 3 metals in a row are all isoelectric to neon (have the same electron configuration).
Are they all going to be the same size? Is there something else, besides just the same electron configuration going on here? Think about the rest of the atom parts.
What’s going on in the nucleus?

7. Cation Electron configuration
Period Trend for Cation size…
Cations:
Na+1
Mg+2
Al+3
Cation Electron configuration
total electrons
Number of protons
11p+
12p+
13p+
With more and more protons pulling the SAME NUMBER OF ELECTRONS, each cation will get smaller and smaller.
The period trend for cation size is decreasing.

8. Electron configuration
Period Trend for Anion size…
Anions:
N-3
O-2
F-1
Electron configuration
Number of protons
Write the period trend for anion size.

9. Electron configuration
Period Trend for Anion size…
Anions:
N-3
O-2
F-1
Electron configuration
total electrons
Number of protons
7p+
8p+
9p+
With more and more protons pulling the SAME NUMBER OF ELECTRONS, each anion will get smaller and smaller.
The period trend for anion size is decreasing.

10. Recap:
Cations are always lots smaller than their atoms, because the cations lose orbitals when they lose electrons.
Anions are always slightly larger than their atoms because the extra electrons stretch the orbital a bit as they repel from each other.
The group trend for cation size is increasing (because they add orbitals)
The group trend for anion size is increasing (because they add orbitals)
The period trend for cation size is decreasing (because with the same number of electrons in the same number of orbitals, the additional protons in the nucleus pull the anions tighter and tighter together.)
The period trend for anion size is decreasing (because with the same number of electrons in the same number of orbitals, the additional protons in the nucleus pull the anions tighter and tighter together.)

11. Take out your homework 1-3 assignments Homework # 1
1. What is the definition of nuclear charge of an atom?
2. What are the net nuclear charges for these 10 atoms? Mg Sc V Cr Ir Au Hg Pb Al P
3. What is the GROUP TREND for net nuclear charge going down any group?
4. What is the PERIOD TREND for the net nuclear charge going across any period?
HOMEWORK # 2
1. List all atoms in Period 4. Show the atomic masses for each (use ACTUAL
VALUES on periodic table, DO NOT ROUND THESE.) Describe the PERIOD TREND for atomic masses.
2. Explain what happens with Cobalt and Nickel. Does this destroy the trend?
3. Explain why atoms get SMALLER going across periods.

12. You should hand in the Review Lab #2 now.
Forget the boxes for now, answer the questions:
1. Describe the GROUP TREND (going down a group) for Atomic Radius.
Describe the PERIOD TREND for Atomic Radius as you go ACROSS A PERIOD.
You should hand in the Review Lab #2 now.
You should also hand in the Boyle in a Bottle Lab now.
You should hand in these 3 HW’s now.
You should read the diary for Periodic Table Tonight
You should finish up the Review Lab #3 by Friday