1. Electron Configuration and Periodic Trends
Periodic Trends of the Elements
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2. Valence Electrons The valence electrons
Determine the chemical properties of the elements.
Are the electrons in the s and p sublevels in the highest energy level/outermost energy level
Are related to the Group Number of the element.
Example: Phosphorus has 5 valence electrons
5 valence electrons
P = Group (15) s22s22p6 3s23p3

3. Group Number and Valence Electrons
All the elements in a group have the same number
of valence electrons…this is why those elements behave similarly!
Example:
Elements in Group (2) have two (2) valence
electrons.
Be 1s2 2s2
Mg 1s2 2s2 2p6 3s2
Ca 1s2 2s2 2p6 3s2 3p6 4s2
Sr 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2

4. Periodic Table and Valence Electrons: Add this info to your periodic table

5. Learning Check State the number of valence electrons for each: A. O
1) ) 6 3) 8
B. Al
1) ) 3 3) 1
C. Cl
1) 2 2) 5 3) 7

6. Solution State the number of valence electrons for each. A. O 2) 6
2) 6
B. Al
2) 3
C. Cl
3) 7

7. Learning Check State the number of valence electrons for each.
A. Calcium
1) ) 2 3) 3
B. Group (16)
1) ) 4 3) 6
C. Tin
1) ) 4 3) 14

8. Solution State the number of valence electrons for each. A. Calcium
2) 2
B. Group (16)
3) 6
C. Tin
2) 4

9. Learning Check
State the number of valence electrons for each. Hint—look at the sublevel/s of the highest energy level
A. 1s2 2s2 2p6 3s2 3p3
B. 1s2 2s2 2p6 3s2 3p64s2 3d104p4
C. 1s22s22p5

10. Solution State the number of valence electrons for each.
A. 1s2 2s2 2p6 3s2 3p3 5
B. 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4 6
C. 1s22s22p

11. Atomic Size / Radius Atomic radius
Is the distance from the nucleus to the valence electrons
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12. Atomic Radius Within A Group
Atomic radius increases
Going down each group of representative elements.
More energy levels = bigger size
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13. Atomic Radius Across a Period
Atomic radius decreases
Going from left to right across a period.
Each proton added increases nuclear attraction for valence electrons. This attraction causes the atom to shrink.

14. Learning Check Select the element in each pair with the larger
atomic radius.
A. Li or K
B. K or Br
C. P or Cl

15. Solution Select the element in each pair with the larger
atomic radius.
A. K
B. K
C. P

16. Ion Size/Radius An ion is an atom that has lost or gained electrons
Losses and gains occur to create filled outer energy levels…causes stability
We will do more with ions when we get to the next chapter so for now just listen and think…

17. Sizes of Metal Atoms and Ions
A positive ion
Has lost its valence electrons.
Metals lose VE
Is smaller (about half the size) than its corresponding metal atom.
The protons there can pull harder when there are fewer electrons, making the ion shrink in comparison
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18. Example: Size of Sodium Ion
The sodium ion Na+
Forms when the Na atom loses one electron from the 3rd energy level.
Is smaller than a Na atom. Both have 11 protons, but those 11 protons can pull harder on 10 electrons than they can on 11.

19. Sizes of Nonmetal Atoms and Ions
A negative ion
Has a complete octet.
Is an atom that gained valence electrons.
Nonmetals gain VE
Is larger (about twice the size) than its corresponding nonmetal atom.
Since the # of protons is the same, there is an imbalance in how hard they can pull…this expands the size of the ion
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Publishing as Benjamin Cummings

20. Example: Size of Fluoride Ion
The fluoride ion F-
Forms when a valence electron is added.
Has increased repulsions due to the added valence electron.
Is larger than F atom

21. Learning Check Which is larger in each of the following?
1. a. K or b. K+
2. a. Al or b. Al3+
3. a. S2- or b. S
Which is smaller in each of the following?
4. a. N or b. N
5. a. Cl or b. Cl-
6. a. Sr2+ or b. Sr

22. Solution 1. Which is larger in each of the following? A. K > K+
B. Al > Al3+
C. S2- > S
2. Which is smaller in each of the following?
A. N < N3-
B. Cl < Cl-
C. Sr2+< Sr

23. Ionization Energy Ionization energy
Is the energy it takes to remove a valence electron.
IE tells us how difficult it is to take a valence electron
Large IE means it is HARD to take an electron; Small IE means it is EASY to take an electron
Na(g) + Energy of Na+(g) e-
Ionization +

24. Ionization Energy Metals have 1-3 valence electrons.
Lower ionization energies.
They “want” to lose electrons, so the IE will be lower
If they lose their valence electrons, their new outermost energy levels will be full
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25. Ionization Energy Nonmetals have 5-7 valence electrons.
Have higher ionization energies.
They “need” more electrons to get an octet, so it is harder to take electrons from them…higher IE’s.
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26. Ionization Energy Nobel gases have
Complete octets or full outer energy levels (He has two valence electrons.)
Have the highest ionization energies in each period.
Very hard to take an electron from an element with the octet!
Copyright © by Pearson Education, Inc.
Publishing as Benjamin Cummings

27. Learning Check Select the element in each pair with the higher
Ionization energy.
1. A. Li or B. K
2. A. K or B. Br
3. A. P or B. Cl

28. Solution Select the element in each pair with the higher
Ionization energy.
A. Li
B. Br
C. Cl

29. Electronegativity

30. Electronegativity
EN = how much an element wants to NOT share electrons equally when it forms a bond with another atom…wants to hog them! METALS—not very EN; don’t want more e- NONMETALS—very EN; want more e- Fluorine is the MOST electronegative element. Why are there no EN’s listed for noble gases????

31. Electronegativity