1. The Periodic Table
Periodic Properties

2. Atomic Size
Atomic size: the radius of an atom (distance from nucleus to electron cloud) is considered.
Measured in angstroms (A) : 1 cm = 1x108 A
Periodic Trend: Atomic size within a group increases and decreases as atomic number increases.
Atomic size increases
Atomic size increases

3. Ionic Size
Some elements tend to gain or lose electrons to form ions.
Metals lose electrons and form positive ions called cations.
Nonmetals gain electrons and form negative ions called anions.
Fe2+
Iron has a 2+ charge (oxidation number) because it lost 2 electons.

4. Ionic Size Periodic Trend:
Cations are smaller than original atom. Losing electrons means the nucleus has a greater attraction for electrons remaining.
Anions are bigger than original atom. Gaining electrons means the nucleus has less attraction for a greater number of electrons.

5. Learning Check
For each of the following sets of atoms and ions, decide which is the smallest.
a.  Na, Na+
b.  Cl, Cl-
c.  Na+, Cl-
d.  H+, H, H-
e.  Fe2+, Fe3+
f.  F-, Ne, Na+

6. Classwork
Textbook p 255 #1,2
p # 3,4
p 266 # 19

7. Octet Rule
States that atoms tend to gain or lose electrons in order to obtain a full set of eight valence electrons to become stable (exception elements in period 1)
s and p sublevels are filled
Ex. Sodium atom, Na ion
1s22s22p63s1
Fluorine atom, F ion
1s22s22p5

8. Ionization energy Energy required to remove an electron from an atom.
Measured when element is in gaseous state.
First ionization energy: energy required to remove first electron from the highest occupied energy level.
Measured in kJ/mol
Some elements have second, third… ionization energy, meaning they can lose more than one electron forming positive ions.

9. Trends in ionization energy
Ionization energy increases
Ionization energy increases

10. Trends in ionization energy
Ionization energy increases within a period.
As the number of protons increases, the nuclear force increases making harder to remove an electron.
Ionization energy decreases within a group.
As the size of the atom increases, nuclear force has a smaller effect on electrons on highest energy level.
Ionization energy increases
Ionization energy increases

11. Electronegativity
Is the ability of an element to attract electrons when the atom is in a compound.
Noble gases are omitted because they don’t form many compounds.
Most electronegative element is Fluorine
Least electronegative element is cesium

12. Trends in electronegativity
Electronegativity increases
Electronegativity increases