1. Chemical Periodicity
Ch. 14

2. Periodic Table Revisited
14-1

3. Periodic Table Revisited
In 1871 Russian chemist, Dmitri Mendeleev, created the periodic table organized by atomic mass
Now it is organized by increasing atomic #
Physical and chemical properties within a group are similar

4. Mendeleev’s Table

6. Periodic Trends
14-2

7. #1 Patterns in Atomic Size
Atomic size of an element decreases across a period (from left to right)
As the # of electrons in an energy level increases, they are held more tightly to the nucleus (attracted to the protons inside)
Atomic size increases down a group (from top to bottom)
As the # of energy levels increases the size of the atom increases

8. Draw on white blank periodic table

9. Size increases down a group!

10. Size decreases across a period

12. #2 Patterns in Ionic Size
Ions are charged atoms.
Cation: positive ion, loses electrons; smaller than atom because lost electrons
B+3 is smaller than B
Lose an energy level + more protons than electrons so held tighter = smaller
Anion: negative ion, gains electrons; larger than atom because gained electrons
N-3 is larger than N
More electrons than protons, not as attracted to nucleus = larger

14. Ionic size decreases across a period
(Larger) Li+  Be+2  B+3 (Smaller)
(Larger) N-3  O-2  F- (Smaller)
Ionic size increases down a group.

15. Draw on Blank Periodic Table Ionic Size Decreases across
Ionic Size Increases Down

16. #3 Ionization Energy
Ionization energy: The energy required to remove an electron from an atom
Measures the resistance to the loss of electrons
Ionization energy increases as you move across a period (left to right)
Easy to remove electron from cations (L) not anions (R)
Ionization energy decreases as you move down a group (top to bottom)
Farther away from the nucleus, the easier it is to remove an electron

17. Draw on white blank periodic table
CATIONS
ANIONS -1 +1
Ionization Energy
decreases +2 +3 -3 -2

18. #4 Electronegativity
Electronegativity measures the ability of an atom to attract, or gain, electrons
Ex: Cation does not want to gain electrons while anions do; anions have a higher electronegativity
Electronegativity increases across a period
Anions (R) have greater ability to gain electrons than cations (L)
Electronegativity decreases down a group
Less ability to attract electrons when the size is larger (farther from the nucleus with positive protons)

19. Draw on white blank periodic table
Decreasing EN

20. Summary of Periodic Trends
Across Period
(Left to Right)
Down Group
(top to bottom)
Atomic Size
Ionic Size
Ionization Energy
Electronegativity

21. Summary of Periodic Trends
Across
(Left to Right)
Down
(top to bottom)
Atomic Size
Decrease
Increase
Ionic Size
Ionization E
Electronegativity