1. Periodic Trends
Notes in packet

2. Octet Rule and Ions
Octet Rule – atoms ability to gain, lose or share electrons to acquire a full set of 8 valence electrons

3. Octet Rule and Ions
What will determine if an atom will gain or lose electrons?
Metals have 1, 2, or 3 valence electrons – they will lose electrons (cations)
Nonmetals have 5, 6, or 7 valence electrons – they will gain electrons (anions)

4. Effective Nuclear Charge
Charge felt by a particular electron
Inner electron shields outer electrons from the nuclear charge
More energy levels, higher shielding effect for outer electrons

5. Effective Nuclear Charge

6. Trend: Effective Nuclear Charge Exceptions
There are some areas of the periodic table that do not follow the general trend.
Due to electron pair repulsion
Due to s shielding p
Due to electron pair repulsion in doubly occupied orbitals

7. Coulombic Attraction Force between positive and negative charges
Directly proportional to charge size
As charge increases, attraction increases
Inversely proportional to distance
As distance increases, attraction decreases

8. Electronegativity
Indicates the relative ability of its atoms to attract electrons in a chemical bond

9. Electronegativity Trend
Generally increases
Why would we see higher electro-negativities in the nonmetals than we do in the metals?
Horizontal trend takes precedence over vertical trend!!!
Generally increases

10. Let’s Practice
Between the elements As, Sn and Sb, which is the most electronegative? As
Between the elements Sr, Ba and Ra, which is the most electronegative? Sr

11. More Practice
Circle the element with the largest electronegativity and underline the smallest electronegativity:
1. Si N
2. Ca Al
3. Pb Bi Sn
4. O S F Cl
5. Ge Si P As S
Which elements are excluded from electronegativity? Why?

12. Reactivity Trend
Nonmetals increase
Why is the trend in reactivity different for metal and nonmetals?
Nonmetals increase
Metals increase
Metals react because of the fact that they lose electrons. Fr has the lowest electronegativity meaning it’s the metal that loses electrons the easiest. Nonmetals react because of the fact that they gain electrons. F has the highest electronegativity meaning that it gain electrons easily.
Metals increase

13. Practice Questions
As you go from left to right across the periodic table, what happens to reactivity of the elements? Why?
 As you go from top to bottom down the periodic table, what happens to reactivity of the elements? Why?
 How are reactivity and the valence electrons related?

14. First Ionization Energy
Energy required to remove an electron from an atom
A measure of how strongly a nucleus hangs onto its valence electrons
High ionization energy = atoms less likely to form positive ions
Low ionization energy = an atom loses an outer electron easily

15. First Ionization Energy Trend
Generally increases
Why do we see the same trend in electro-negativity as we do first ionization energy?
Why do metals have low first ionization energies?
Horizontal trend takes precedence over vertical trend!!!
Generally increases

16. Second Ionization Energy
The energy required to remove 2nd (or more) electrons from the atom

17. Let’s Practice
Consider the table of ionization energies for element X shown below.
Ionization Energy in kJ/mol
(a) In which group will X be found? Explain. __________________________________
(b) Predict the formula of X’s bromide. __________________________
1st
2nd
3rd
4th
5th
6th
737
1450
7732
10540
13360
17995

18. Atomic Radius
Half the distance between adjacent nuclei of identical atoms

19. Vertical trend takes precedence over horizontal trend!!!
Atomic Radius
Vertical trend takes precedence over horizontal trend!!!
Why does atomic radius increase as we move down a group?
Why does atomic radius increase as we move right to left across a period?
Generally increases
Across a period, we are not adding any additional energy levels but we are adding protons which increase nuclear charge. Since the additional electrons are in the same energy level, they are not shielded from increased nuclear charge which brings the energy level in closer to the nucleus.
Generally increases

20. Let’s Practice
Between the elements Po, Te, I, which one has the largest atomic radius? Po
Between the elements Sc, Rb and Cr, which one has the smallest atomic radius? Cr

21. Ionic Radius The size of the atom once it has formed an ion
Positive ions form smaller atoms
Negative ions form larger atoms

22. Ionic Radius Trend Nonmetals increase Metals increase

23. Let’s Practice
Between the elements N, O and P, which will form the smallest ion? O
In the group below, which is the largest and which is the smallest?
Mg2+ Br-1 K B3+ P3-
Largest = K, Smallest=B3+

24. More Practice
1. Which diagram best represents the relationship between the diameter of a sodium atom and the diameter of a positive sodium ion?
a. b. c.
1. In each of the following pairs, pick the larger species. Explain you answer in each case.
(a) Cu and Cu2+ 
(b) F and F- 

25. Shielding Effect Shielding of outer electrons by inner electrons
Shields the outer electrons from the positive pull of the nucleus

26. Shielding Effect Trend
Why is shielding constant moving across the period?
Generally increases
We are not adding any additional energy levels so not putting anything else between valence electrons and the nucleus.
Shielding is constant across the period