1. Section 6.3
Periodic Trends

2. Objectives Compare period and group trends of several properties
Relate period and group trends in atomic radii to electron configuration

3. Atomic Radius Electron cloud no defined edges
90% probability of finding an electron
Size varies from substance to substance

4. Radius: Metals
½ distance between adjacent nuclei in a crystal of the element

5. Radius: Nonmetals
½ distance between nuclei of identical atoms that are chemically bonded

6. Trends within Periods The decrease from left to right
All in same principal energy level
Increased nuclear charge as you move to the right, which draws electrons closer to the nucleus.

7. Trends within Groups Increase from top to bottom
Nuclear charge increases
Electrons are added to higher principal energy levels
Increase number of shells

8. Periodic Trends: Atomic Radius
DECREASES I N C R E A S

11. Ions
Atoms that gain or lose electrons
negative or positive charge

12. Ionic Radius
+ charge = smaller radius
- charge= larger radius

13. Lose Electrons/ +

14. Gain Electrons/ -

15. Trends within Periods L to R: positive ions’ radii decreases
5A: Size of larger negative ions decreases

16. Trends within Groups
Ionic radii of both positive and negative ions increase as you move down a group

17. Ionization Energy
Energy required to remove an electron from a gaseous atom
Energy required to remove first electron is the first ionization energy
Nuclei’s strength of hold on valence electrons

18. Ions and Ionization Energy
1A has low IE form positive ions
8A has high IE do not form ions

19. Beyond the 1st IE
2nd ionization energy = amount of energy needed to remove an electron from a 1+ ion
3rd IE = to remove e- from a 2+ ion

20. Trends within Periods First ionization energies increase L to R
Inc. nuclear charge= inc hold on e-

21. Trends within groups
First ionization energies decrease from top to bottom
Valence electrons are farther from nucleus

22. Periodic Trends: Ionization Energy
INCREASES D E C R A S

24. Octet rule
Atoms tend to gain lose or share electrons to acquire a full set of 8 valence electrons
Used to determine type of ion an element is likely to form

25. Electronegativity
Relative ability of an atom to attract electrons in a chemical bond.
Arbitrary units called Paulings

26. Electronegativity Trends
Increases from L to R
Except Noble Gases
REASON: nuclear charge increases, more attraction to electrons in its outermost energy level
Increases from top to bottom
REASON: electrons are further away from the nucleus and better shielded from the nuclear charge

27. Periodic Trends: Electronegativity
INCREASES D E C R A S