The document explains the structure of the periodic table, categorizing elements into representative, transition, and inner transition elements. It outlines periodic properties such as atomic radius, ionization energy, electron affinity, and electronegativity, including their trends across periods and down groups. Significant definitions and trends are also provided, such as that atomic radius decreases across a period and increases down a group, while ionization energy and electronegativity generally increase across a period and decrease down a group.

1. 1
THE PERIODIC TABLE
A listing of elements in an array such that
atomic numbers increase from left to right
and elements in any column have similar
outer electronic structures.
ROWS = PERIODS
COLUMNS = GROUPS

2. 2
CLASSES OF ELEMENTS
1. REPRESENTATIVE ELEMENTS
The differentiating electrons fill the s and p
orbitals, Groups IA-VIIA and Group O. These are
sometimes called MAIN GROUP ELEMENTS
2. TRANSITION ELEMENTS
The differentiating electrons fill d-orbitals.
3. INNER TRANSITION ELEMENTS
Differentiating electrons fill the f-orbitals
4f - Lanthanides
5f - Actinides

3. 3
PERIODIC PROPERTIES
1. ATOMIC RADIUS
2. IONISATION ENERGY
3. ELECTRON AFFINITY
4. ELECTRONEGATIVITY

4. 4
ATOMIC RADIUS
nm
0.099
2
0.198
Radius
Atomic
Cl2 

Definition: This is one half the distance between centers of
touching atoms.
r
TRENDS:
(i) Decreases as we move across a period from left to right in the PT.
(ii) Increases as we move down a Group in the PT.

5. 5
RATIONALE:
Across a Period
Effective nuclear charge experienced by an electron at the outer
edge of an atom is given by:
Zeff = Z – S
Where: Z = Actual nuclear charge = At. No.
S = No. of electrons between the outer electron and the
nucleus.
For main group elements
S = No. of electrons in inner complete energy levels.
e.g. for Mg with 1s2 2s2 2p6 3s2 then S = 10.
Therefore:
Zeff should increase as we move across a period from left to right in
the PT.
RESULT Atomic radius decreases from left to right of PT.

6. 6
Down the Group:
 Down the Group, Zeff experienced by an outer electron
remains essentially constant.
 However, the distance of the electron from the nucleus
increases with the Principal Quantum Number.
At. No. S Zeff
H = 1s1 1 1
Li = 1s2 2s1 3 2 1
Na = 1s2 2s2 2p6 3s1 11 10 1
K = 1s2 2s2 2p6 3s2 3p6 4s1 19 18 1
 Hence: Atomic Radius increases as we move down the
Group in the PT.

7. 7
FIRST IONISATION ENERGY
Definition:
 The energy that must be absorbed to remove the outermost
electron from a gaseous atom.
Mg(g)  Mg+
(g) + e-
TRENDS:
i. Increases as we move across a period (from LEFT to RIGHT)
in the Periodic Table.
ii. Decreases as we move down a Group in the Periodic Table.
There are some exceptions:
e.g. 1st ionization Energy actually decreases as one moves across
from Be (900 kJ/mol) to B (801 kJ/mol).
Be = 1s2 2s2
B = 1s2 2s2 2p1
Since 2p level is higher in Energy than 2s
it easier to remove an electron from 2p

8. 8
Ionization energy does not increase smoothly as we remove
successive electrons
e.g. Na: 1s2 2s2 2p6 3s1
IE1 = 496 kJ/mol. From 3s and hence removed easily since
it is far from the nucleus.
IE2 = 4561 kJ/mol.
IE3 = 6913 kJ/mol
ANY COMMENT ON THE TREND?

9. 9
ELECTRON AFFINITY
Definition: The energy change that occurs when an electron is
added to a gaseous atom or ion.
i.e. (i) M(g) + e-  M-
(g) [Neutral atom]
(ii) M+
(g) + e-  M(g) [an ion of charge +1]
TRENDS:
(i) Across a Period
In general electron affinities become more negative (stronger
attraction for an electron) from LEFT to RIGHT of the PT.

10. 10
(ii) Down a Group:
Electron affinities differ very little as we go down a group.
REASONS
• Average distance of electron from nucleus steadily
increase, and electron-nuclear attraction should steadily
decrease.
• Orbitals become increasingly spread out and electron-
electron repulsion with the added electron decreases.
 These two factors counterbalance.

11. 11
ELECTRONEGATIVITY
Definition:
The ability of an atom to attract electrons to itself in a
chemical bond.
TRENDS:
(i) Increases as we move across a Period from LEFT to
RIGHT. i.e. From the most metallic to the most non-
metallic element.
(ii)Decreases as we move down a group (excluding a few
exceptions)
i.e. From the most non-metallic to the most metallic
element.

12. 12
NOTE:
Electronegativity varies with the TYPE of chemical environment in which
an element is in.
Eg. Chlorine : in PCl3 or in ClO3
-
The electronegativity difference between two atoms is a measure of the
polarity of the bond between them:
The greater the difference in electronegativity, the more polar is the bond.
Most electronegative element : F = 4.0
Least electronegative element : Cs = 0.79
e.g. HF  H+  F-
H  electronegativity = 2.2}
F  electronegativity = 4.0}
Therefore H-F is a POLAR BOND