1. OBJECTIVES: Students will understand the Shielding Effect.
Students will explain the Atomic Radius Trend found on the Periodic Table.

2. What is the Shielding Effect?
The attraction of the valence electrons to the protons in the nucleus. The further away they are from the protons, the less the attraction.
What is the Shielding Effect?

3. As you move down a group- electrons are placed on higher energy levels- more shielded from the protons. As you move across a period – electrons are added to the same energy level- less shielded from the protons.
How Does it Work?

4. Due to the Shielding Effect – three trends have been observed and explained: 1. Atomic Radius 2. Ionization Energy 3. Electronegativity

5. What are Periodic Trends?
Trends are properties in that increase or decrease in a period or group for a specific property.
No transition metals, too many exceptions.
What are Periodic Trends?

6. Which Way?

7. Half the distance between two nuclei of the same atom (basically the size of the atom).
Trend #1 Atomic Radius

8. What does it look like? Examples:
Put in increasing order (smallest to largest):
K, Kr, Ge
Cs,, Na, K
Show them the why of column vs row.
What does it look like?

9. BELLWORK 11/09/15
Which of these alkali metals has the largest atomic radius? Cs, Fr, Li, or Na?

10. OBJECTIVES:
Students will analyze the trends for ionization energy and electronegativity.

11. Let’s Review How to Identify Trends
We define trends based on how the properties change relative to: A. Groups B. Periods

12. How do we Read the Arrows?
INCREASE
INCREASE
INCREASE
INCREASE

13. Trend #2 Ionization Energy
The amount of energy required to remove an electron from an atom.
The strength that an atom holds onto its electrons.
More shielding = less ionization energy
Less Shielding = more ionization energy (electrons held tight)
Always start with the outer electrons that come off first and we work our way in.

14. How does it work? Examples:
Put in increasing order (smallest to largest):
K, Kr, Ge
Cs, Na, K
As you move across the periodic table you will gain electrons, therefore the more electrons that an atom has the less likely it will want to loose those electrons, giving it a higher ionization energy. It decreases down the group because you are getting larger and larger atoms so they are farther from the positive charge meaning they are not held as tight and they are easier to loose.

15. Trend #3 Electronegativity
The ability for an atom to attract an electron (usually from another atom).
Noble gases left out of this trend, they don’t attract any electrons.
More shielding= Less electronegativity
Less Shielding = more electronegativity
Hey you! Get over here!!

16. How it works: Examples: Put in increasing order (smallest to largest):
K, Kr, Ge
Cs, Na, K

17. BELLWORK 11/10/15
Periodic trends vary as we move across the periodic table. In general, as you move across a row in the periodic table
A) ionic size increases
B) atomic radius decreases
C) nuclear charge decreases
D) ionization energy decreases

18. PRACTICE #1
Rank the following elements by increasing (smallest to largest)atomic radius: C, Al, O, K

19. PRACTICE #2
Rank the following elements by increasing electronegativity (lowest to highest ) : S, O, Ne, and Al

20. Classwork / Homework
Periodic Trend Worksheet
Answer Key