Transcript Ch. 14 Notes

Chemical Periodicity
Ch. 14
Periodic Table Revisited
14-1
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
Mendeleev’s Table
Periodic Trends
14-2
#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
Add pattern #1 to periodic table
Size increases down a group!
Size decreases across a period
#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
• 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.
Ionic Size
Decreases
across
Ionic Size
Increases
Down
Add
pattern
#2 to
periodic
table
#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
Add pattern #3 to periodic table
CATIONS
ANIONS
-1
+1
Ionization
Energy
decreases
+2
+3
0
-3
-2
0
#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)
Add pattern #4 to periodic table
Decreasing EN
Across:
1. Dec. Atomic Size 2. Dec. Ionic Size
3. Inc. IE
Down:
4. Inc. EN
1. Inc. Atomic Size
2. Inc. Ionic Size
3. Dec. IE
4. Dec. EN
Summary of Periodic Trends
Trend
Atomic Size
Ionic Size
Ionization
Energy
Electronegativity
Across Period
(Left to Right)
Down Group
(top to bottom)
Summary of Periodic Trends
Trend
Across
(Left to Right)
Down
(top to bottom)
Atomic Size
Decrease
Increase
Ionic Size
Decrease
Increase
Ionization E
Increase
Decrease
Electronegativity
Increase
Decrease