The Periodic Table &
Formation of Ions
Development of the Periodic Table
Mendeleev:
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Considered to be the father of the periodic
table
Arranged elements by increasing atomic
mass
Placed elements with similar properties in
columns
Left blank spaces for undiscovered elements
Was able to accurately predict properties of
the undiscovered elements
The Modern Periodic Table
Moseley
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Arranged elements by increasing atomic
number
Gave a clearer pattern of periodic properties
Periodic Law: there is a periodic repetition of
chemical and physical properties of elements
when they are arranged by increasing atomic
number
Arrangement of the table
Groups/Families
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Columns of elements
Numbered 1 to 18
Elements have similar properties
Elements have the same # of valence electrons
Periods
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Rows of elements
Numbered 1 to 7
Corresponds to number of energy levels of an
atom
Groups with Special Names
Group 1:
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Alkali Metals
Group 2:
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Alkaline Earth Metals
Groups 3 -12:
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Transition Metals
Group 17
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Halogens
Group 18
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Noble Gases
Each group contains elements with the
same number of valence electrons
Group #
1
2
3-12
13
14
15
16
17
18
# of valence electrons
1
2
varies
3
4
5
6
7
8
Example 1
Without drawing electron configurations,
determine the number of valence electrons
for each of the following:
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A. Calcium
B. Neon
C. Sodium
D. Aluminum
E. Sulfur
Periodic Trends
Valence electrons
Atomic Radius
Ionization Energy: Energy required to
remove an electron from a neutral atom
Electronegativity: The attraction of an
atom for shared electrons in a covalent
bond
Atomic Radius
Increases from top to bottom in a group
Decreases from left to right across a
period
Example 2
Arrange each of the following in order of
increasing atomic radius (smallest 
largest)
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A. Calcium, Magnesium, Barium
B. Fluorine, Iodine, Chlorine
C. Calcium, Arsenic, Bromine
D. Chlorine, Fluorine, Oxygen
Ionization Energy
Increases from left to right across a period
Decreases from top to bottom in a group
Example 3
Place the following in order of increasing
ionization energy (lowest  highest)
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A. Sulfur, Oxygen, Selenium
B. Calcium, Magnesium, Beryllium
C. Lithium, Fluorine, Nitrogen
D. Carbon, Silicon, Nitrogen
Electronegatvity
Increases from left to right across a period
Decreases from top to bottom in a group
Example 4
Determine the most electronegative
element in each pair
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A. Calcium, sulfur
B. sulfur, chlorine
C. potassium, bromine
D. Silicon, phosphorus
Octet Rule
Typically, elements want to have 8
valence electrons (except hydrogen and
helium) in order to be stable
Noble gases are stable because they have
8 valence electrons
Other elements will lose, gain, or share
electrons in order to have 8 valence
Becoming Stable
Remember atoms are neutral because
they have equal #’s of protons and
electrons
When an atom gains or loses electrons,
this equality is upset…
The atom is no longer neutral…and is no
longer called an atom
Ions
An ion is an atom that has an electric
charge because it has lost or gained
electrons
If an atom loses electrons, its charge will
become positive. It is called a cation.
If an atom gains electrons, its charge will
become negative. It is called an anion.
On the Periodic Table
Group
1
2
3 -12
13
14
15
16
17
18
Charge of Ion
+1
+2
Varies
+3
-3
-2
-1
Do not form ions
Ionic Charges
The number of electrons that an atom will
gain or lose in order to become stable
determines its ionic charge
Metals lose electrons and have + charge
(These are called cations)
Nonmetals gain electrons and have –
charge (These are called anions)
Size of Ions
Cations (+ charges) are smaller than their
parent atoms
Anions (- charges) are larger than their
parent atoms
Example 5
Determine the ionic charge for each of the
following. Indicate if it is a cation or an
anion:
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A. Magnesium
B. Chlorine
C. Oxygen
D. Sodium
E. Nitrogen
Naming Ions
If the ion is positive…name it the atom’s
name followed by the word ion
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Example: Sodium is Na1+…its name is Sodium
ion
If the ion is negative…change the atom’s
name to have an –ide ending then write the
word ion
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Example: Chlorine is Cl1-…its name is chloride
ion
Example 6
Indicate the ionic charge and the name of
the ion formed from each of the following
elements:
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A. Potassium
B. Bromine
C. Aluminum
D. Cesium
E. Fluorine
Element
# Valence
electrons
Ionic Charge
Symbol
Name of ion
# of protons
# of electrons
Mg
F
O
K
Na
Al