The Periodic Table
The Periodic Table
Is a device used to classify elements according to their atomic number.
This classification is the basis of the PERIODIC LAW, which states that some of the physical and
many of the chemical properties of the elements are periodic function of their atomic number.
The elements are arranged in rows and columns. The PERIODS are the seven horizontal rows in
the periodic table.
The GROUPS are the eighteen vertical columns in the periodic table.
A. Classification of
Elements
Representative Elements
Are the elements that are labeled from group 1A to 7A. elements.
They are usually called the family A elements.
The outermost s or p sublevels of these elements are only partially filled.
The period number indicates the element’s highest main energy LEVEL.
The representative elements are divided into 7 groups:
7 Groups of Representative Elements
Group 1A – Alkali Metals
Group 3A – Boron Family
Electronic configuration ends in ns1
Electronic configuration ends in ns2 np1
1 valence electron
 3 valence electrons
Oxidation state is +1
Group 4A – Carbon Family
Group 2A – Alkaline Earth Metals
Electronic configuration ends in ns2 np2
Electronic configuration ends in ns2
 4 valence electrons
2 valence electrons
Oxidation state is +2
7 Groups of Representative Elements
Group 5A – Nitrogen Family
Group 7A – Halogen Family
Electronic configuration ends in ns2 np3
Electronic configuration ends in ns2 np5
 5 valence electrons
 7 valence electrons
Can gain 1 electron
Group 6A – Oxygen Family
Electronic configuration ends in ns2 np4
 6 valence electrons
Can gain 2 electrons
All are nonmetals and exist as diatomic
molecules (F2, Cl2, Br2, I2, At2)
Noble Gases
Noble gases are the elements that belong to group 8A.
They are also called INERT GASES because they have a very
little tendency to react with anything else.
Their electronic configuration ends in ns2 np6 except for
Helium.
Transition Metals
Transition metals are the elements that belong to group 1B
to 8B.
Their electronic configuration ends in s2d1 to s2d10 in the d
block.
They also exhibit several oxidation states.
Inner Transition Metals
Inner transition metals are located at the bottom of the
periodic table and are placed between groups 3B and 4B.
They are divided into two main groups:
Lanthanide series in period 6
Actinide series in period 7.
The elements here belong to the f block.
B. Valence Electrons
Valence Electrons
The number of electrons in the highest main energy level or
outermost shell of an atom is referred as VALENCE
ELECTRONS.
For any representative element, the group number is equal
to the valence electrons.
C. Periodic Variations
Atomic Size
The atomic size decreases as you go from left to right
across any period in the periodic table.
This is so because as you go through a period, the number
of electrons and protons increases by one thereby
increasing the nuclear charge.
The greater the nuclear charge, the greater the full of
electrons toward the nucleus making the atom smaller.
The atomic size increases from top to bottom due to the
addition of energy levels.
Figure 2. Atomic Radii of representative Elements
Atomic size
decreases as
you go from left
to right
Atomic size
increases
from top to
bottom
Example Problem
Arrange the following elements in order of decreasing
size.
(i) Na, P, Si, Cl, Mg = Na, Mg, Si, P, Cl
(ii) Ca, Al, Ni, Ba, B = Ba, Ca, Ni, Al, B
(iii) Cs, Y, Nb, Si, Ar = Cs, Y, Nb, Si, Y
Metallic Property
Elements in the table are classified as metals, non metals
and metalloids.
The elements on the left of the black zigzag line are metals
while the elements on the right are nonmetals.
Therefore, the elements become more non-metallic going
across a period from left to right of the periodic table.
Within a group, there is an increase in metallic properties
from top to bottom.
Example Problem
more nonmetallic from
left to right of
the periodic
table.
increase in
metallic properties
from top to
bottom
Arrange the following elements in order of increasing metallic properties.
(i) P, Mo, Ag, Cs, Rb = Cs, Ag, Mo, Rb, P - Christian
Cs, Rb, Mo, Ag, P – Vincent
P, Ag, Mo, Rb, Cs - Raf
(ii) Cl, Br, I, F, Sn, Te =
F, Cl, Br, Sn, Te, I – Gary
F, Cl, Br, I, Te, Sn - Keith
Ionization Energy
Ionization Energy is the amount of energy needed to
remove an electron from atom or ion.
Ionization energy decreases as we go down a group.
Ionization energy increases from left to right across the
periodic table. (The more protons in the nucleus, the stronger
the attraction of the nucleus to electrons).
Example Problem
Ionization energy increases from
left to right across the periodic
table.
Arrange the following elements in order of increasing ionization energy.
(i) Sr, Rb, Mn, Sc, Al, C = Rb, Sr, Sc, Mn, Al, C
(ii) S, O, Ag, Cd, Cs, Mo = Cs, Mo, Ag, Cd, S, O
Electronegativity
Electronegativity of an atom is defined as tendency of that
atom to attract electrons towards itself.
Non metals tend to gain electrons while metals generally
lose one or more electrons to attain a stable configuration.
Therefore, electronegativity increases from left to right
across a period in the periodic table and decreases from top
to bottom within a group.
Figure 3: Electronegativity Values of Elements
Example Problem
Choose the one with highest electronegativity.
(i) Sr, Rb, Mn, Sc, Al, F = Rb, F,
(ii) Y, O, Mo, Cd, Cs, Co = Cs, O
D. Summary of
Periodic Trends
Atomic Size and Metallic Property
Increases
Increases
Ionization Energy and Electronegativity
Decreases
Decreases
E. Oxidation Number
(Oxidation State)
Oxidation Number
The Oxidation Number is a positive or negative value that
not only describes the combining capacity of an atom but
also indicates how may electrons are arrange in a
compound.
These oxidation numbers are assigned to electronic
structure and electronegativity for several key elements.
The following general rules for assigning
or determining oxidation numbers
1. The oxidation number of a pure element is zero.
O2 oxidation number is zero (0)
Na oxidation number is zero (0)
2. The oxidation number of an ion is the charge of the ion.
O-2 oxidation number is -2
H+1 oxidation number is +1
The following general rules for assigning
or determining oxidation numbers:
3. The algebraic sum of the oxidation numbers of all atoms in the
formula for compound is zero.
Find oxidation number of P for the compound H3PO4
Let x be the oxidation number of P
3(+1) + x + (4)(-2) = 0
3+x–8=0
x = -3 +8
x = +5
The following general rules for assigning
or determining oxidation numbers
4. The sum of the oxidation numbers of the atoms in a polyatomic ion
must be equal to the charge on the ion.
Find oxidation number of P for the compound PO4-3
Let x be the oxidation number of P
x + (4)(-2) = -3
x + (-8) = -3
x = -3 +8
x = +5
Some Common Oxidation Numbers:
A. Group IA elements are always +1
B. Group IIA elements are always +2
C. Group VIIA elements are -1, except when element is combined
with one having a higher electronegativity
D. Hydrogen is always +1 except in metal hydrides where it is -1, such
as NaH and CaH2
E. Oxygen is always -2, except in peroxides where it is -1, such as
H2O2 and Na2O2
F. SEATWORK