Transcript Trends on the Periodic Table

Trends on the Periodic Table
Today we’re filling in blanks and
drawing arrows. Lucky you!
Periodic Trends
• Based on where elements are on the
periodic table, you can sequence them
(put them in order) by:
– Atomic radius (size)
– Ionization energy
– Electron affinity
– Electronegativity
Atomic Radius
• Atomic radius is the size of a single atom
of any given element.
• Increases as we move down the periodic
table. Why??
As we move down, we are adding extra energy
levels (more shells).
Example: Think of lithium and sodium’s
electron configuration:
Li:
Na:
2 shells
Li
Na
3 shells
Atomic Radius
• Decreases as we move from left to right.
We don’t add extra energy levels, but we add more
protons in the nucleus, and they pull harder on the
electrons.
Example: Think of carbon and nitrogen:
C: 1s2 2s2 2p4 (only has 6 p+ pulling in the middle)
N: 1s2 2s2 2p5 (now has 7 p+ pulling in the middle)
Atomic Radius Trend
Q: Which element is the largest? Which is the smallest?
Fr
He
Ionization Energy
• Ionization energy: the amount of energy
needed to remove an electron from a
gaseous atom or ion.
– Metals tend to lose electrons (low ionization
energy).
– Nonmetals tend to gain electrons (high
ionization energy). They hate giving up the
ones they’ve already got!
Ionization Energy Trend
Q: Which element has the highest ionization energy? He
Which has the lowest? Fr
Q: How does this relate to atomic radius (especially going down a
family)?
The farther away electrons are from the
nucleus, the less the nucleus can “hang on”
to them.
Electron Affinity
• Electron affinity: the ability of an atom to
accept an electron.
• Goes in the same direction as ionization
energy. Why?
– Because if it takes a lot of energy to remove
an electron, the atom likes the ones it has
enough to steal some more.
• Let’s look at Chlorine…
Electron Affinity Trend
Q: Which element has the highest electron affinity? F
Which has the lowest? Fr
Q: How does this relate to number of valence electrons?
Nonmetals have more than 4 and steal electrons;
metals have less than 4 and lose electrons.
Electronegativity
• Electronegativity - The ability to pull
electrons closer when bonded to another
atom.
• Sometimes 2 atoms will share electrons
in a bond.
• When this happens, usually one atom has
more “pull” on the electrons = more
electronegativity.
Less
electronegativity
More
electronegativity
Electronegativity Trend:
**Noble gases
don’t usually
react, so we
don’t consider
their electronegativities.
Q: Which element has the highest electronegativity? F
Which has the lowest? Fr
Q: How does this relate to electron affinity?
More affinity = More pull when shared = More
electronegativity
Ionic Radii
• When something completely loses or gains an
electron, the size of the ion changes.
• Metals will lose electrons in the outer shell
making them smaller.
Draw
lithium on
your
notes!
Ionic Radii
• Nonmetals will steal electrons and add
them to their outer shell, making them
bigger.
Draw
nitrogen
on your
notes!
Homework!
• Homework worksheet due on Friday!
• You should do it because it is good
practice and there is a
• QUIZ ON FRIDAY!!!