1. Relative Size
Ionization Energy
Electron Affinity
Electronegativity

2. General Rule - Relative Size
When looking at the periodic table, atoms get bigger:
Top to bottom
Right to left

3. Top to Bottom Down a Column
The atoms get bigger because
the electrons are in
a higher energy level.

4. Left to Right Across a Row
The atoms get smaller because the
positive charge in the middle of
the atom is more concentrated so
it’s sucking the electrons in closer.

5. Relative Size Chart

6. *Positive Ions and Negative Ions*
Positive Ions: If an atom loses all of its valence (outermost) electrons, it’s going down to the next energy level so it’s getting smaller.
Losing electrons = positive charge
More protons than electrons = + charge

7. *Positive Ions and Negative Ions*
Negative Ions: If an atom gains electrons it has a negative charge. The nucleus stays the same but the radius gets bigger because there are more electrons.
Gaining electrons = negative charge
More electrons than protons = - charge

8. Which one has a larger radius?
Sample Problems - Part 1
Which one has a larger radius?
(a) Ti or Ni
(b) F or F-1
(c) Ba or Hf
(d) Ca or Ca+2

9. Sample Problems - Part 2 Which one has a smaller radius? (a) K or Cs
(b) Cs or Os
(c) O or O-2
(d) Na or Na+1

10. Challenge Excluding the Noble Gases because they’re special:
What is the smallest atom?
____________________
What is the largest atom?

11. Ionization Energy
Definition: The energy required to remove an electron from an atom.
First Ionization Energy
The energy needed to remove the most loosely held electron from an atom.
Measured in kilojoules per mole (kj/mol).

12. General Rule - Ionization Energy
Ionization Energy increases going across periods (rows) - increases as atomic number increases.
Ionization Energy decreases going down groups (columns).

13. Classifying Elements based on Ionization Energy
Metals
Tend to lose electrons to become more stable
Low ionization energy
Nonmetals
Tend to gain electrons to become more stable
High ionization energy
Noble Gases
Have an octet so they’re already stable
Very high ionization energy

14. Electron Affinity
Definition: the attraction of an atom for an additional electron
Metals tend to have low electron affinities.
Nonmetals tend to have high electron affinities.

15. Sample Problems - Part 3 Which one has a lower ionization energy?
(a) Cl or Kr
(b) Iron or Iodine
Which one has a higher electron affinity?
(a) Oxygen or Barium
(b) Na or Cl

16. Electronegativity
Definition: the relative attraction of an atom for a shared pair of electrons.
The difference in electronegativities increases as the bond strength between two atoms increases.
Metals tend to have low electronegativities.
Nonmetals tend to have high electronegativities.

17. Electronegativity Chart

18. Sample Problems - Part 4 Which atom has a higher electronegativity?
(a) Ca or C
(b) Titanium or Tellurium
Which atom has a lower electronegativity?
(a) Br or Be
(b) Strontium or Selenium

19. Factors that affect Ionization Energy, Electron Affinity, and Electronegativity
Distance from nucleus
Stability

20. Connections between Ionization Energy, Electron Affinity, and Electronegativity
In general, as Electron Affinity increases, Ionization Energy increases.
Electron Affinity and Electronegativity increase going across a period (left to right).
Ionization Energy and Electronegativity increase going up a column (bottom to top).