1. Trends & the Periodic Table

2. Trends
More than 20 properties change in predictable way based on location of elements in PT
Ex: density, melting point, atomic radius, ionization energy, electronegativity

3. Atomic radius
Ionization energy
Electronegativity

4. Atomic Radius
Atomic radius = 1/2 distance between neighboring nuclei in molecule or crystal
“size” varies bit from substance to substance

5. Cannot measure electron cloud:
X-ray diffraction pinpoints nuclei to measure distance

6. Trends:
Atoms get larger as go down a column
– ↑ principal energy levels

7. Going down column 1: Fr 7 Cs 6 Rb 5 K 4
2-8-1 Na 3
2-1 Li 2 1 H
Configuration
Element
Period
↑ energy levels as go down, so
makes sense that atoms get larger

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Li: Group 1 Period 2
Cs: Group 1 Period 6

9. Going across row 2: 2-8 Ne VIIIA or 18 2-7 F VIIA or 17 2-6 O
VIA or 16
2-5 N
VA or 15
2-4 C
IVA or 14
2-3 B
IIIA or 13
2-2 Be
IIA or 2
2-1 Li
IA or 1
Configuration
Element
Family
You are still adding electrons – shouldn’t they get larger?! Atoms actually get a bit smaller as you go across a row What’s going on?

10. What do you remember about charge?
opposites attract/like charges repel
valence electrons are pulled into atom by (+) charge of nucleus
the greater the (+) charge, the more pulling power

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as go L to R across row the size ↓ a bit because of greater “proton pulling power (PPP)”

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size  as you go  &
size  as you go 

13. Ionization Energy
amount energy required to remove electron from an atom
Ionization energy = energy required to remove most loosely held valence electron

14. Trends in ionization energy
What do you think happens to the ionization energy as you go down a column of the periodic table?
As you go across a row?

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Same group:
Cs’ valence electron farther away from nucleus so electrostatic attraction is much weaker (easier to steal electron away from Cs)

16. easier to steal electron from Li than Ne Li: less PPP than Ne
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Same row:
easier to steal electron from Li than Ne
Li: less PPP than Ne

17. Trends in ionization energy
Ionization energy ↓ as go down column
– easier to remove valence electron as gets farther away (↑ # electron levels)
Ionization energy ↑ as go across row
– it’s more difficult to remove valence electron due to ↑ PPP

18. Electronegativity Ability of atom to attract electrons in a bond
Noble gases do not form bonds
are inactive
don’t have electronegativity values
Unit = Pauling
Fluorine: most electronegative element (4.0 Paulings)

19. Trends in electronegativity
Related to “proton pulling power (PPP)”
↑left to right across a row
↓top to bottom of a column

20. Electronegativity increases in direction of arrow from Fr towards F (most electronegative element)

21. Reactivity of Metals metals are losers!
judge reactivity of metals by how easily they give up electrons
most active metals: Fr (#1) and Cs (#2)
Reactivity metals: ↑ as ionization energy ↓

22. Trends for Reactivity of Metals (AKA: Metallic Character)
Increases as go down column
Easier to lose electrons!
Decreases as go across row
Harder to lose electrons!

23. Reactivity of Non-metals
non-metals are winners!
judge reactivity of non-metals by how easily they gain electrons
most active non-metal: fluorine
reactivity non-metals: ↑ as electronegativity ↑

24. Trend for Reactivity of Non-metals depends on PPP
↑ as go across row (left to right)
↓ as go down column (top to bottom)
shielded by more inner-shell electrons

25. Ionic Size Relative to Parent Atom
Depends on if (+) ion or (-) ion
How do you create a positive ion?
How do you create a negative ion?
Remove electrons
Add electrons

26. How do you know if an atom gains or loses electrons?
Octet rule: magic # 8
Metals have 1, 2, or 3 valence electrons
easier to lose them
Nonmetals have 5, 6, or 7 valence electrons
easier to gain more
Noble gases: have 8 so don’t form ions

27. Positive ions or cations
Cations always smaller than parent atom
lost electrons therefore smaller in size

28. Negative ions or anions
Anions always larger than parent atom
gained electrons therefore larger in size