1. 5.2 PERIODIC TRENDS
A. Atomic Radius
The atomic radius of a chemical element is a measure of the size of its atoms and is the _distance from the nucleus to the boundary of the surrounding cloud of electrons.

2. PERIOD TREND (across - left to right): Radius
As atomic # INCREASES, AR _decreases_
For each element across a period, one proton and one electron are added to the outermost energy level.
As NUCLEAR CHARGE increases (nucleus is more ++), electrons are pulled _inward____
(opposites attract)

3. PERIOD TREND (across - left to right): Radius
Practice: K or Kr has the larger atomic radius
Practice: K has the larger atomic radius

4. GROUP TREND (down - top to bottom)
As atomic # INCREASES down a group, AR __increases__
For each element down a group, an ENERGY LEVEL is added to the atom.
Nuclear charge increases, but __shielding__also increases.
SHIELDING – as energy levels are added, electrons are less affected by positively charged nucleus because electrons repel each other.
Practice: Ba / Mg has the larger atomic radius

5. GROUP TREND (down - top to bottom)
Practice: Ba or Mg has the larger atomic radius (AR)
Practice: Ba has the larger atomic radius

6. Ionization Energy
Ionization Energy is the energy required to remove the outermost_electron from an atom (in kilojoules)

7. Ionization Energy PERIOD TREND (across - left to right):
As atomic # INCREASES, IE __increases
Nuclear charge increases; ___electrons__
are held more __closely______ to the nucleus
Also, outer energy level is closer to being an _octet__
Practice: Ca / Br has a higher IE

8. Ionization Energy Practice: Br has a higher IE
Practice: Ca or Br has a higher IE
Practice: Br has a higher IE

9. Ionization Energy GROUP TREND (down - top to bottom)
As atomic # INCREASES , IE _decreases_______
Outer electrons are in __higher_
energy levels
Farther from nucleus, more ___easily_______ removed
Practice: Na / Cs has a higher IE

10. Ionization Energy Practice: Na / has a higher IE GROUP TREND
(down - top to bottom)
Practice: Na / Cs has a higher IE
Practice: Na / has a higher IE

11. Challenge:
Challenge: Which element (from the entire periodic table) has the highest IE?___
_He_____

12. Electronegativity

13. Electronegativity
Electronegativity is a measure of an atom’s ability to _take____ another atom’s electrons (no units). Electronegativity is abbreviated “EN”.

14. Electronegativity PERIOD TREND (across - left to right):
 As atomic # INCREASES EN ___increases_____.
 Metals tend to___lose________ electrons
 Nonmetals tend to ____gain________electrons
(to fulfill the ____octet__________ Rule)
Practice: Be / O has a higher EN

15. Electronegativity GROUP TREND (down - top to bottom)
As atomic # INCREASES, EN ___decreases_______
Elements at __top___ of group have e– closely held by nucleus because they are closest to nucleus.
Elements at bottom of group have more _distance____ between nucleus and outer e–
Practice: N / Sb has a higher EN 

16. Electronegativity Practice: N has a higher EN Fi Electronegativity
Why are noble gases not EN?
They have complete octet. There is no driving force for them to take or give up electrons

17. Reactivity
Reactivity refers to how __likely________ an atom is to react with other substances.
Reactivity depends on ...
1. How easily electrons can be removed (__ionization energy___)
2. How easily atoms grab electrons (___electronegativity_____)

18. Reactivity Reactivity of Metals – low ionization energy
PERIOD TREND (across - left to right):- As atomic # INCREASES, reactivity ____decreases_________
GROUP TREND (down - top to bottom) - As atomic # INCREASES, reactivity ____increases_____________
WHY? If IE is low, an atom is more likely to lose an electron, which results in a chemical reaction with another atom

19. Reactivity Reactivity of Nonmetals – high electronegativity
PERIOD TREND (across - left to right): - As atomic # INCREASES, reactivity _____increases_________
GROUP TREND (down - top to bottom): - As atomic # INCREASES, reactivity _____decreases______
WHY? IF EN is high, the atom takes electrons from other atoms more easily, which results in a chemical reaction.

20. NONMETALS – higher EN

21. Atomic Radius

22. Electronegativity

23. Ionization Energy

24. Reactivity

25. A Trick to Remembering the Trends:
Snowman that falls over:
Atomic Radius
Metal Reactivity
A&M likes to stand at football games!

26. A Trick to Remembering the Trends:
Snowman standing on his head and then he falls over:
Electronegativity **EINstein like to do
Ionization Energy headstands!!
Nonmetal Reactivity

28. The End
Test on 12/17/2015