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TOPIC: Trends in the Periodic Table: Atomic Radius
Do Now: get out pack and open to p.10
Trends
• more than 20 properties change in predictable way based location of elements on PT
• some properties: - anyone know where we can find these numbers?!
– Density– melting point/boiling point– atomic radius– ionization energy– electronegativity
When you’re done it will look like this so leave room for writing!
2-8-18-32-18-8-1Fr7
2-8-18-18-8-1Cs6
2-8-18-8-1Rb5
2-8-8-1K4
2-8-1Na3
2-1Li2
1H1
ConfigurationElementPeriod
Going down column 1:
increasing # energy levels as go down
Increasing number of energy levels
Atomic Radius• Atomic radius: defined as ½ distance
between neighboring nuclei in molecule or crystal
• Affected by
1. # of energy
levels2. Proton Pulling
Power
Incr
easi
ng n
umbe
r of
ene
rgy
leve
ls
Increasing Atomic Radius
previous | index | next
Li: Group 1 Period 2 Cs: Group 1 Period 6
Cs has more energy levels, so it’s bigger
2-8NeVIIIA or 18
2-7FVIIA or 17
2-6OVIA or 16
2-5NVA or 15
2-4CIVA or 14
2-3BIIIA or 132-2BeIIA or 22-1LiIA or 1
ConfigurationElementFamily
As we go across, elements gain electrons, but they are getting smaller!
Incr
easi
ng n
umbe
r of
ene
rgy
leve
ls
Incr
easi
ng A
tom
ic R
adiu
s
Decreasing Atomic Radius
previous | index | next
Why does this happen..
• As you go from left to right, you again more protons (the atomic number increases)
• You have greater “proton pulling power” – Remember the nucleus is + and the electrons
are - so they get pulled towards the nucleus• The more protons your have, the more Proton
Pulling Power
as go across row size tends to decrease a bit because of greater PPP “proton pulling power”
previous | index | next
What the inner electrons do….
They Shield the charge felt by the valance electrons.
previous | index | next
H and He: only elements whose valence electrons feel full nuclear charge (pull)
NOTHING TO SHIELD THEM
Positive ions (cations)
• Formed by loss of electrons
• Cations always smaller than parent atom
Ca
2e
8e
8e
2e
Ca+2
2e
8e
8e
Ca
Negative ions or (anions)
• Formed by gain of electrons
• Anions always larger than parent atom
