Post on 21-May-2015
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November 18November 18thth & 19 & 19thth, , 20092009
Periodic Periodic TrendsTrends
Periodic LawPeriodic Law
When elements are arranged in When elements are arranged in
order of increasing atomic #, order of increasing atomic #,
elements with similar properties elements with similar properties
appear at regular intervals appear at regular intervals
(periodically).(periodically).
Periodic PropertiesPeriodic Properties
© 1998 LOGAL
Atomic Radius
Size of atom
First Ionization Energy
Energy required to remove one e- from a neutral atom.
© 1998 LOGAL
Electronegativity
How much an atom pulls
Electrons towards itself in a bond
Atomic RadiusAtomic Radius
Size of atomSize of atom
0
50
100
150
200
250
0 5 10 15 20Atomic Number
Atomic Radius (pm)
Li
ArNe
KNa
1
2
3
4 5
6
7
Atomic RadiusAtomic Radius
Increases to the LEFT and DOWN Francium is the largest atom
Atomic RadiusAtomic RadiusWhy larger going down?Why larger going down?
Higher energy levels have larger orbitalsHigher energy levels have larger orbitals
Why smaller to the right? Why smaller to the right?
ShieldingShielding – core electrons block the – core electrons block the attraction between the nucleus and the attraction between the nucleus and the valence electronsvalence electrons
Increased nuclear charge without additional Increased nuclear charge without additional shielding pulls electrons in tightershielding pulls electrons in tighter
Ionization EnergyIonization EnergyEnergy required to remove an electronEnergy required to remove an electron
It ALWAYS requires some energy to remove an electron!!It ALWAYS requires some energy to remove an electron!!
0
500
1000
1500
2000
2500
0 5 10 15 20Atomic Number
1st Ionization Energy (kJ)
KNaLi
Ar
NeHe
1
2
3
4 5
6
7
Ionization EnergyIonization Energy
Increases UP and to the RIGHT Helium has the highest Ionization Energy
Ionization EnergyIonization EnergyWhy opposite of atomic radius?Why opposite of atomic radius?
In small atoms, eIn small atoms, e-- are close to the nucleus where the attraction is stronger and they are harder to pull off are close to the nucleus where the attraction is stronger and they are harder to pull off
Small atom = high ionization energySmall atom = high ionization energy
In larger atoms, the valence electrons are easier to pull offIn larger atoms, the valence electrons are easier to pull off
Large atom = low ionization energyLarge atom = low ionization energy
ElectronegativityElectronegativityAbility of an atom to pull Ability of an atom to pull
electrons towards itself in a bond.electrons towards itself in a bond.
1
2
3
4 5
6
7
Increases UP and to the RIGHT Fluorine has the highest electronegativity Noble gases have no electronegativity
because they don’t form bonds
Electronegativity
Why opposite of atomic radius?
In small atoms, there is less shielding so
the protons pull harder on electrons
Small atom = high electronegativity
In larger atoms, there is more shielding
Large atom = low electronegativity
ElectronegativityElectronegativity
ExamplesExamples
Which atom has the larger radius?Which atom has the larger radius?
Be or Ba
Ca or Br
Ba
Ca
ExamplesExamples
Which atom has the higher Ionization Energy?Which atom has the higher Ionization Energy?
N or Bi
Ba or Ne
N
Ne
ExamplesExamples
Which atom has the higher electronegativity?Which atom has the higher electronegativity?
Li or C
Cr or Kr
C
Kr?