Transcript III. Periodic Trends

Warm-up
Periodic Law
• When elements are arranged in order of
increasing atomic #, elements with
similar properties appear at regular
intervals.
Atomic Radius (pm)
250
200
150
100
50
0
0
5
10
Atomic Number
15
20
Chemical Reactivity
• Families- similar valence e- within a group results in
similar chemical properties
• Metals- increase in reactivity down a family &
decrease in reactivity across the period
• Nonmetals- decrease in reactivity down a family &
increase in reactivity across the period
1
2
3
4
5
6
7
Periodic Properties
• Atomic Radius
– size of atom
© 1998 LOGAL
• Atomic Radius
– Decreases across the period and increases
down a family
I
n
c
r
e
a
s
e
s
1
2
3
4
5
6
7
decreases
• Why is it larger as you move down a
group?
– Higher energy levels have larger orbitals
– Shielding - core e- block the attraction
between the nucleus and the valence e-
• Why is it smaller to the right of a
period?
– Increased nuclear charge without additional
shielding pulls e- in tighter
• First Ionization Energy
– Energy required to remove
one e- from a neutral atom.
• First Ionization Energy
– Increases across a period & decreases down
a group
d
e
c
r
e
a
s
e
1
2
3
4
5
6
7
increase
• Smaller atoms hold the electrons
tighter (they are closer to the
nucleus!) so it takes more energy to
remove those electrons.
• The larger the atom is the farther away
the electrons are so it doesn’t take as
much energy to remove the electron.
• Successive Ionization Energies
– Large jump in I.E. occurs when a CORE e- is
removed.
– Mg
Core e-
1st I.E.
736 kJ
2nd I.E.
1,445 kJ
3rd I.E.
7,730 kJ
• Successive Ionization Energies
– Large jump in I.E. occurs when a CORE
e- is removed.
– Al
Core e-
1st I.E.
577 kJ
2nd I.E.
1,815 kJ
3rd I.E.
2,740 kJ
4th I.E.
11,600 kJ
Periodic Properties
• Melting/Boiling Point
Melting/Boiling Point
• Melting/Boiling Point
– Highest in the middle of a period.
1
2
3
4
5
6
7
Periodic Properties
• Electronegativity – measure of how strongly
an atom attracts electrons when it is in a
compound
– applies when an atom is in a compound NOT alone
• Fluorine (the most electronegative element) is
assigned a 4.0 and then all the others were
determined by comparison
Electronegativity
Ionic Radius
• Ionic Radius
– Cations (+)
• lose e-
• smaller
– Anions (–)
• gain e• larger
© 2002 Prentice-Hall, Inc.
Examples
• Which atom has the larger radius?
Be
or Ba
Ba
Ca
or Br
Ca
Examples
• Which atom has the higher 1st I.E.?
Nor Bi
N
Ba
Ne
or Ne
Examples
• Which atom has the higher
melting/boiling point?
Li
or C
C
Cr
or Kr
Cr
Examples
• Which particle has the larger radius?
S or S2Al
or
S23+
Al
Al