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
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)

3. Atomic Radius
The distance from the center of the nucleus to the electron cloud

4. Atomic Radius Why does atomic radius increase as we move down a group?
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

5. 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

6. Electronegativity
Indicates the relative ability of an atom to attract electrons in a chemical bond

7. Electronegativity Trend
Generally increases
Why would we see higher electro-negativities in the nonmetals than we do in the metals?
Generally increases

8. 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

9. 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?

10. 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?

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

12. Ionic Radius Trend Nonmetals increase Metals increase

13. 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- 

14. 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+

15. 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 = it takes more energy to remove an electron
Low ionization energy = it takes less energy to remove an electron

16. 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?
Generally increases

17. There is a general increase in the first ionization energy from sodium to argon. Why?
The size of the atom is decreasing from left to right, which means electrons are being pulled closer to the nucleus, and therefore, it would be harder to remove an electron= high ionization energy.

18. Which group on the PT has the highest ionization energy?
Noble gases because they have a full valence shell, which means it would be difficult to remove their electrons, therefore it would require a lot of energy

19. Why does ionization energy decrease down a group?
There are more energy levels as you go down a group, therefore valence electrons are further from the nucleus and it would make it easier to remove an electron

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

21. 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

22. 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