Warm-up
• Calculate the frequency of green light
with a wavelength of 530 x 10-9 m.
• What is the energy of a 8.42 x 1014 Hz
wave?
March 2nd, 2015
Period Trends
Periodic Table - Review
Russian, Dmitri Mendeleev
 When he arranged elements by atomic
mass, he found similar properties at
certain levels
 Published first periodic table in 1869
 Left empty spaces where he predicted
undiscovered elements should be

 Noble gases didn’t exist
Mendeleev’s PT
Periodic Table
1911, Henry Moseley (English) found
that the pattern worked best if arranged
by number of protons
 Our current periodic tables use this
method of arrangement
 Properties of elements change in a
predictable way : trend
 Groups : Columns (up and down)
 Periods : Rows (left and right)

Trend #1 – Atomic Radius
The atomic radius of an
element is a measure of
the size of its atoms.
 Typically the distance
from the nucleus to the
edge of the electron
cloud
 However, boundary is
not well-defined

Radius decreases as you move
from left-to-right across a period.
Radius
increases
as you
move
down
a group.
Which atom has a larger
radius?

Na or Cs?
 Hint* Who’s closer to Francium?

Na or S?

S or O?
 Hint* Who’s lower in the group?
Cations and Anions
Remember that an ion is an atom
with a charge.
 An Anion is an atom with a
negative charge

 Anions form when valence electrons
are added to the outer energy level.

A Cation is an atom with a positive
charge.
 Cations form when valence electrons
are removed from the outer energy
level.
Trend #2 Ionic Radii
An atom gets bigger
when electrons are
added.
 An atom gets smaller
when electrons are
removed.

Ionic Radius decreases as you move
from left-to-right across a period.
Ionic
Radius
increases
as you
move
down
a group.
Trend #3 – Ionization Energy
An electron can be removed from an
atom if enough energy is used
 Ionization energy – the energy required
to remove one electron from a gaseous
neutral atom

Ionization Energy, cont.

Metals freely give their valence
electron(s)
 “costs” less energy

Non-metals hold onto electrons more
strongly
 “must pay” more energy to get rid of
electrons
Ionization energy increases
from left-to-right across a period
Ionization
energy
increases
moving
up
a group
Which has higher IE?

Li or F?
 Hint* which is the non-metal?

K or S?

Ba or Li?
 Hint* which holds onto its electrons more?
○ Which has its valence electrons closer to the
nucleus?
Trend #4 - Electronegativity


Applies when an atom is in a compound NOT
alone
Electronegativity – measure of how strongly
an atom attracts electrons when it is in a
compound
 How much of a bully is that element when in the
compound
○ Atoms “little kids”
○ Electrons “the toys”

Fluorine (the most electronegative element –
“biggest bully”) is assigned a 4.0 and then all
the others were determined by comparison
Electronegativity increases from
left-to-right across a period
Electronegativity
decreases
as you move
down
a group
Which has higher electronegativity?

Sr or Be?
 Hint* Which is higher up and therefore closer
to Fluorine?

P or O?

Si or Cl?
Notebook
• Go back through the notes and draw all
of the trends that we discussed onto
your periodic table in your notebook.
• Use map pencils and markers to help
differentiate the different trends.
Content & Language
Objectives
Warm-Up
Periodic Trends
HW: None
March 2nd, 2015
Warm-up
1. Choose the atom in each pair that has
the largest atomic radius.
a) Al F
b) Sr O
c) Br I
2. Circle the atom in each pair that has
the greater ionization energy.
d) Rb Be e) Na Cs
f) Cl Sn
March 3rd, 2015
Content & Language
Objectives
Warm-Up
Periodic Trends Worksheet
HW: Finish Worksheet
March 3rd, 2015