The document discusses the modern periodic table and atomic structure. It describes how Henry Moseley's studies in the early 1900s proved that an element's properties depend on its atomic number rather than atomic mass. The periodic table is now arranged based on increasing atomic number. There are 7 periods and 18 groups in the periodic table. The number of valence electrons corresponds to the group number for groups 1 and 2. Transition elements are those in groups 3 through 12 and have properties between metals and non-metals.

1. Atomic structure and the modern
Periodic table

2. HENRY MOSELY
• English physicist
• The studies conducted by Mosley
regarding the properties of elements
related to their position in the periodic
table finally proved that the basic
properties of elements depend on their
atomic numbers and not on atomic
masses .

3. Modern Periodic Table
• When more and more elements were
discovered ,small changes were to be made in
Mendeleev ‘s periodic table .
• In 1914 , Mosley suggested that elements
should be arranged in the ascending order of
the atomic number .

4. Modern Periodic Law
• Properties of elements depend on their
atomic numbers .
• When elements are arranged in the
ascending order of their atomic numbers
there is a repetition of their properties at
fixed intervals

5. Peculiarities of modern periodic table
• There are 7 periods in periodic table
• There are 18 groups in the periodic table.

6. Representation of each element in
modern periodic table
Atomic number 3
Symbol Li
Name Lithium
Atomic mass 6.9
Electronic distribution 2 , 1

7. Peculiarities of periods of periodic
table
• One of the period is given below :-
•
• In the period , as the atomic number
increases the number of valence electron
also increases .
• After fixed intervals , the distribution of
electrons in the outermost shell gets
repeated in the same way .
Li Be B C N O F Ne

8. Peculiarities of ‘groups ‘ of periodic
table
• The electron distribution of elements in group 1 and
group 2 is as given below: -
The number of valence electrons of the elements that
come in same groups are equal .
The elements in the same group shows similar properties
since the number of valence electrons are equal and
general electron structure are the same .
Group 1 Group 2
H 1
Li 2,1 Be 2,2
Na 2,8,1 Mg 2,8,2
K 2,8,8,1 Ca 2,8,8,2

9. Relationship between the group
number and the number of valence
electrons
Group
number
Name of the element
family
Number
of
valence
electrons
Valency
1 Alkali metal family 1 1
2 Alkaline earth metal
family
2 2
13 Boron family 3 3
14 Carbon family 4 4
15 Nitrogen family 5 3
16 Oxygen family 6 2
17 Halogen family 7 1
18 Noble gas family 8 0

10. There is a relation between group number and
valence electrons .
In group 1 and group 2 ,number of valence electrons
is equal to the group number .
Elements 13 and 18 , 10 is added to valence electron
to get the group number .
By knowing the number of valence electrons we can
find the group number and valency .
Valency is the number of electrons released or
accepted by the atom of an element to complete its
octet .

11. The elements in group 3 to 12 are
called transition elements .
The position of transition elements is
in between the metals and
non – metals .
They are so called because they
indicate a gradual progressive change
from metallic to non – metallic
properties .

12. THANK YOU