Turn to page 3 in the Unit Note Packet
History of the Periodic Table
 In the mid-1800’s, Dimitri Mendeleev published a table of
all of the known elements, 70 elements to be exact.
 Not until Dmitri Mendeleev, no one had come up with a
way to organize the elements.
 Mendeleev came up with the first working system of filing the
elements. Mendeleev’s table was arranged based on the
increasing atomic mass.
 He listed the elements with similar chemical and physical
properties in columns on his periodic table. They were in
order of increasing atomic mass.
History of the Periodic Table
 Mendeleev left gaps in the table since there were no
current elements that seemed to fit those spots
 Those elements were eventually discovered and they fit
perfectly into an open spot.
 Today, we list the elements in order of increasing
atomic number. We owe this arrangement to Henry
Moseley
History of the Periodic Table
 The modern Periodic Table is arranged by increasing
atomic number
 Increases from left to right, and top to bottom
 This establishes the periodic law
 When the elements are arranged in order of increasing
atomic #, there is a periodic repetition of their physical
& chemical properties
 Groups- Vertical columns on the periodic table
 Periods- Horizontal rows of elements- 1-7
• Periodicity- When the elements are arranged in
order of increasing atomic number, there is a periodic
repetition of their physical and chemical properties.
Groups…Here’s Where the
Periodic Table Gets Useful!!
 Elements in
the same
group have
similar
chemical and
physical
properties!!
 (Mendeleev did that on
purpose.)
Why??
• They have the same
number of valence
electrons.
• They will form the same
kinds of ions (have the
same ____________).
Groups or Families on the
Periodic Table
 Columns are also grouped
into families.
 Families may be one or several
columns put together.
 Families have names rather
than numbers. (Just like your
family has a common last
name.)
 Representative Elements- All of the Group A
Elements 1A-8A
Trend # 1
Atomic Radius or Size
Group Trend:
 The Trend: As you move down a group on the periodic
table, the atomic radius or size of an atom increases.
 The Reason: This is because each row adds a new
energy level for the electrons.
 Examples:
Which is larger: Mg or Ca
Calcium!
Which is smaller: F or Br?
Fluorine!
Period Trend:
 The Trend: As you move across a period from left to
right, the atomic radius or size of an atom decreases.
 The Reason: This is because of the nucleus getting
stronger as you add more protons. This pulls the
electrons closer to the nucleus.
 Examples:
Which is smaller: C or F?
Fluorine!
Which is larger: Ba or Cs?
Cs!
A Trick to Remembering the Trend:
 Snowman standing that then falls over:
 Example: Arrange the following elements in order
of increasing size: Mg, Na, Rb, and Cl
Cl
Mg
Na
Rb
a. K
b. S
c. Sb
d. Ba
e. As
f. C
g. C
h. Cs
i. Ba
j. Si
Trend # 2
First Ionization Energy
 Ionization energy is the amount of energy
required to remove an electron from an element in
its gaseous state.
Li (g)
Li+(g) + e-
• Ionization energy refers to making positive ions
or cations.
• To form a positive ion, an element will lose its
valence electrons on the outermost energy level.
Group Trend:
 The Trend: As you move down a group on the
periodic table, the ionization energy of an atom
decreases.
 Example:
Which has smaller ionization energy: Ba or Ca?
Barium
Which has smaller ionization energy: I or Br?
Iodine
Period Trend:
 The Trend: As you move across a period from left
to right, the ionization energy of an atom increases.
• Examples:
Which is lower in ionization energy: C or F?
Carbon (C)!
Which is higher in ionization energy: Na or Mg?
Magnesium (Mg)!
The Reason:
 As an atom gets larger, the valence
electrons are further from the nucleus,
which means that the nucleus’s pull gets
weaker because the electrons are
farther away.
 The weaker pull means that less energy
is required to remove the electron.
Arrange the following elements in order of decreasing ionization energy:
Mg, Na, Rb, and Cl
Cl
Mg
Na
Rb
A Trick to Remembering the Ionization
Energy Trend:
 Opposite of Atomic Radius:
 Snowman standing on his head that then falls over:
 Example: Arrange the following elements in order of
increasing ionization energy Mg, Na, Rb, and Cl
Rb
Na
Mg
Cl
a. K
b. S
c. Sb
d. Ba
e. As
f. C
g. C
h. Cs
i. Ba
j. Si
Trend # 3
Electronegativity
 Electronegativity is the ability of an atom to gain
an electron in a chemical bond.
 Scientists have assigned values for
eletronegativity that range from zero to four.
The higher values represent the more
electronegative elements.
 Since they are unreactive, the noble gases are not
assigned electronegativity values.
Group Trend:
 The Trend: As you move down a group on the
periodic table, the electronegativity of an atom
decreases.
Examples:
Which is more electronegative: N or P?
Nitrogen (N)!
Which has a smaller electronegativity value: F or Br?
Bromine (Br)!
Period Trend:
 The Trend: As you move across a period from
left to right, the electronegativity of an atom
increases.
 Examples:
 Which is less electronegative: C or O?
Carbon (C)!
Which has a greater electronegativity: Ca or K?
Ca or K?
Calcium (Ca)!
The Reason:
 As an atom gets larger, the valence
electrons are further from the nucleus,
which means that the nucleus’s pull gets
weaker as the electrons move farther
away.
 Smaller elements will be more
electronegative because their nucleus is
closer to the valence electrons and has a
stronger pull on the valence electrons.
A Trick to Remembering the
Electronegativity Trend:
 Opposite atomic radius, same as Ionization energy-
Snowman standing on his head and then he falls over:
 Example: Arrange the following elements in order of
increasing electronegativity: Cd, Cl, Br, and I
Cd
I
Br
Cl
Example: Arrange the following elements in order of increasing
electronegativity:
Cd, Cl, Br, and I
Cd
I
Br
Cl
a. Cr
b. Cl
c. N
d. Sr
e. F
f. F
g. Ne
h. Li
i. Be
j. Ar
Trend # 4
Reactivity - Metals &
Nonmetals
General Notes
 Elements in the same group/family have similar
chemical and physical properties.
 What elements would have similar properties to
sulfur?
answer: O, Se, Te, Po

Note: The Representative Elements are those elements
within the first two families (Groups I and II on the far left) and
the last six families or groups (on the right) of the Periodic Table.
Reactivity of Metals
 Group Trend:
The Trend: For metals, the reactivity of
metals increases as you move down a group.
Examples:
Which metal is more reactive: K or Rb?
Rubidium (Rb)!
Which metal is more reactive: Cu or Au?
Gold (Au)!
Period Trend:
 The Trend: For metals, the reactivity of
metals decreases as you move across the period
from left to right.
 Examples:
Which metal is the least reactive: Ca or Zinc?
Zinc (Zn)!
Arrange the following metals- Na, Mg, Al in
order of increasing reactivity.
Al
Mg
Na
The Reason:
 When metals react, they lose
electrons.
 Metals with low ionization energies
are more reactive, or alkali
metals are more reactive because
they lose electrons more easily.
Reactivity of Nonmetals
 Group Trend:
 The Trend: For nonmetals, the reactivity of
nonmetals decreases as you move down a group.
 Examples:
Which is more reactive: Oxygen or sulfur?
Oxygen (O)!
Which halogen is the most reactive: F, Cl, Br,
or I?
Fluorine (F)!
Period Trend:
 The Trend: For nonmetals, the reactivity of
nonmetals increases as you move across a
period from right to left (excluding the noble
gases).
 Examples:
 Which is more reactive: O or F?
Fluorine (F)!
On period 3, which nonmetal is the most reactive?
Chlorine (Cl)!
The Reason:
 When nonmetals react, they tend to
gain electrons.
 Nonmetals with higher
electronegativities have a stronger pull
on electrons and, therefore gain
electrons easily. In other words,
smaller atoms tend to form negative
ions more easily because the nucleus is
more likely to attract these electrons.
A Trick to Remembering the Trends:
 Snowman that falls over:
Atomic Radius
Metal Reactivity
A&M likes to stand at football games!
A Trick to Remembering the Trends:
 Snowman standing on his head and then he falls
over:
• Electronegativity
• Ionization Energy
 Nonmetal Reactivity
**EINstein like to do
headstands!!
Warm-Up
 What three properties both have the following
trend?
Decreases as you go down the group and
Increases as you go across the period from
right to left
Trend # 5
Ionic Radii
Pg. 10
Comparing Ions In the Same
Group:
 When you are comparing ions of elements in the
same group, follow the same trend as the
atomic radius or size of the atoms.
 Examples:
 Which ion is larger: Mg2+ or Ca2+?
Ca2+ larger
Which ion is smaller N3- or P3-?
N3- smaller
Comparing Ions of the Same
Element:
 As an element gains electrons (gets more negative), it
will become larger.
X2+
X+
x
X-
X2-
 Examples:
 Which ion would be larger: Mg2+ or Mg 2 Mg 2List the ions or atoms in order of increasing size- P+, P2+, P,
P-, P3P2+ P+ P P- P3-
Comparing Isoelectric Ions (Ions with the
Same Number of Electrons)
 If you are comparing different ions or atoms
with the same number of electrons, the largest
substance will have the greatest negative
charge.
Examples:
 List the following elements or ions from largest
to smallest Ne, O2-, F-, Na+, Mg2+
Hint: Atomic radius increases down group, decreases across period
O2-, F-, Ne, Na+, Mg2+
Homework: Complete pg. 11 and
12
Metallic Bonds and shielding
Metallic Bonds
Watch the following video and answer the questions
in your notes.
http://www.youtube.com/watch?v=3uNETGK_sb4
http://www.youtube.com/watch?v=srxNJ03
W_qM
Review Trends
3 factors that affect trends
 Nuclear size or pull (# of protons in nucleus or
location- stronger if smaller atom)
 # of electron levels or shells- more shells farther away
less pull
 Electron shielding- occurs because of electrons in
between them and the nucleus- shields their
attraction* think sitting in back of a rock concert- the
people (Electrons in other shells) are shielding you from
the true enjoyment of the band on stage (the nucleus)
because you can’t see through them or hear as well
Shielding