Transcript Periodic Trends

Periodic Trends
of the periodic table
Periodic Trend?
• if you look at atomic data as you go
across (to the right) a period, or down
a group, there are certain patterns
Trend Summary
Across a
Period
Down a
Group
ionization energy
↑
↓
atomic radius
↓
↑
electronegativity
↑
↓
Trend
(1) Ionization Energy
• recall: an ion is a charged particle
• ionization energy refers to the energy
required to remove an electron from an
atom
• (and ∴ make it an ion)
(1) Ionization Energy
• trend explained:
A
-
+
B
A feels less attraction than B
+
+
• similarly:
across a period
more protons ⇒ greater attraction ⇒ harder to remove e-
(1) Ionization Energy
• trend explained:
-A
+
-
+
B
A feels less attraction than B
• similarly:
down a group
increased distance ⇒ less p-e- attraction ⇒
easier to remove e-
(2) Atomic Radius
• distance from the center to the outside
edge of an atom
– actually based on the radius of a ball that
would hold 90% of the electrons
(2) Atomic Radius
• trend explained:
across a period
more protons ⇒ greater attraction ⇒ e- are pulled closer to nucleus
down a group
increased # e- ⇒ more e- repulsion ⇒ new principle
quantum number ⇒ e- pushed away from nucleus
(3) Electronegativity
• the atom asks itself “how badly do I want an
electron”
– yah…I REALLY want it ⇒ high EN
– meh…I don’t really care ⇒ low EN
• the halogens receive huge gains in stability
when they gain an electron
– they gain a full valence shell!
– they have the highest EN values
(3) Electronegativity
• trend explained:
across a period
higher number of protons ⇒ greater e- attraction
⇒ greater increase in stability
down a group
nucleus does not attract electrons as well
(core electrons “shield” the valence ones)
⇒ less drive to gain an e-
The Full Octet
• remember, atoms like to have full
electron shells
– atoms like full s, full p and full d orbitals,
and work hard to make this happen
– you can see this when you look at the
charges of common ions and figure out the
number of electrons in that ion’s outer shell
Trend Summary
Trend
ionization energy
atomic radius
electronegativity
Across a
Period
Down a
Group