Periodic Trends
Chapter 6
Before we talk about trends…
…we must understand: Shielding Effect
Shielding Effect = the ability of other electrons in orbitals to
shield outer electrons from the effect of the positively
charged nucleus (by repelling them)
Trends in Atomic Size
 Size of an atom expressed as __________________
Does an atom have a fixed radius?
Atomic Radius – half the distance between the nuclei of
two atoms of the same element when they are
joined.
Atomic Radius
Discuss: How do you think Atomic Radius trends…
Down a group…
Across a period…
Atomic Radius: Down a Group
 Down a group, atomic radius: INCREASES
Why? Two things are going on:
1.
Increased positive charge in the nucleus
2.
Increased number of occupied energy levels
What effects do these two things have?
Overall trend:
Atomic Radius: Across a Period
 Across a period, atomic radius: DECREASES
Why?
How many protons & electrons are we increasing by across the
table?
In general, these are added to the _____________________
So…
What about Ions?
 Will cation be bigger or smaller than parent atom?
 Will anion be bigger or smaller than parent atom?
Practice Worksheet
 Pause to Practice!!
Ionization Energy
 Ionization Energy = the energy required to remove an
electron from the outer orbital of an atom
1st Ionization Energy = 1st e removed
2nd Ionization Energy = 2nd removed…and so on…
Ionization Energy…
 INCREASES across a period
Why??
 DECREASES down a group
Why??
Successive Ionization Energies…
Electronegativity
Electronegativity = the ability of an atom to attract
electrons while in a compound
Scale: 0.0 – 4.0
Decreases within a group (Top – Bottom)
Why??
Increases across a period (L – R)
Why??
Electronegativity
Summary of Trends…