The Periodic Table
Atomic Radius (pm)
250
Periodic
Trends
200
150
100
50
0
0
5
10
Atomic Number
15
20
I
II
III
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
Same number of valence electrons = similar properties
Li
1s2 2s1
Na
1s2 2s2 2p6 3s1
In any group, the element BELOW has one more
occupied energy level than does the element ABOVE.
The period that an element is in is the same as the
energy level that its valence electrons are in.
Li  in 2nd period
Na  in 3rd period
val. e- in 2nd
val e- in 3rd
Less Metallic
More Metallic
More Metallic
Less Metallic
Metallicity
Periodic Trends and Factors
There are trends in properties of elements
 left right AND up down trends
Trends
Atomic Radius
Ionic Radius
Ionization Energy
Electronegativity
Factors: Columbic attraction and Sheilding
effect
Periodic Factors
I
II
III
Coulombic attraction depends on…
amount of charge
2+
2–
1+
1–
distance between charges
2+
2–
2+
2–
As we go
–
+
H
++
– –
,
more coulombic
attraction, no new
energy level, more
pull, smaller size
He
+ +
– –
shielding effect: kernel e– “shield” valence e–
from attractive force of the nucleus
K
Li
v.e–
v.e–
tougher to
easier
remove
to remove
–
-- caused by kernel and valence e
repelling each other
As we go
, shielding effect increases.
Atomic Radius
I
II
III
Atomic Radius
The size of a neutral atom
 Increases as we go down
Why?
Add a new energy level each time
(larger orbitals)
Decreases as we go across
Why?
It has do to with coloumbic attraction
(attraction between + and -)
Atomic Radius
IA
IIA
IIIA
IVA
VA
VIA
VIIA
Li
Be
B
C
N
O
F
1.52
1.11
0.88
0.77
0.70
0.66
0.64
Na
Mg
Al
Si
P
S
Cl
1.86
1.60
1.43
1.17
1.10
1.04
0.99
K
Ca
Ga
Ge
As
Se
Br
2.31
1.97
1.22
1.22
1.21
1.17
1.14
Rb
Sr
In
Sn
Sb
Te
I
2.44
2.15
1.62
1.40
1.41
1.37
1.33
Cs
Ba
Tl
Pb
Bi
2.62
2.17
1.71
1.75
1.46
Atomic Radius
Decreases to the LEFT and increases
DOWN
1
2
3
4
5
6
7
Examples
Which atom has the larger radius?
Be or Ba
Ba
Ca or Br
Ca
Ionic Radius
I
II
III
Ionic Radius
Ionic Radius
Cations (+)
lose esmaller
Anions (–)
gain e-
larger
© 2002 Prentice-Hall, Inc.
Ionic Radius
As you go down, the ionic radius
increases due to more energy levels.
As you go across
The ionic radius of metals decreases
until middle of periodic table, slight
increase, and then decrease.
Due to lose or gain of electron
Examples
Which particle has the larger radius?
S or
2S
2S
Al or
3+
Al
Al
Ionization Energy
I
II
III
Ionization Energy
The energy required to remove an
electron from an atom.
Each successive ionization requires more
energy than the previous one.
As we go down, the first ionization energy
decreases (due to shielding).
As we go across, the first ionization
energy increases.
Ionization Energy
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
Ionization Energy
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
Examples
Which atom has the higher 1st I.E.?
N or Bi
N
Ba or Ne
Ne
Electronegativity
I
II
III
Electronegativity
Tendency of an atom to attract electrons
in a chemical bond.
Excludes noble gases.
As you go down, electronegativity
decreases.
As you go across, the electronegativity
increases.
Electronegativity
Why smaller going down?
The higher the energy level, the less
the electron attraction of the atom.
Why larger going across?
As the number of valence electrons
increases, the electron attraction of the
atom increases.
Electronegativity
Values
Lowest values– metals at the far left
Lose electrons
Highest values – nonmetals at the far
right
Gain electrons
Other Periodic Trends
I
II
III
Melting/Boiling Point
Melting/Boiling Point
Highest in the middle of a period.
1
2
3
4
5
6
7
Examples
Which atom has the higher
melting/boiling point?
Li or C
C
Cr or Kr
Cr
Summary
Let’s Recap
I
II
III
Summary of Periodic Trends
Shielding is constant
Atomic radius decreases
Electronegativity decreases
Ionization energy decreases
Ionic size increases
Atomic radius increases
Shielding increases
Ionization energy increases
Electronegativity increases
1A
0
2A
3A 4A 5A 6A 7A
Ionic size (cations)
Ionic size (anions)
decreases
decreases