Modern Periodic Table
The Modern Periodic Table is a tabular display of all the chemical elements , arranged on the basis of their properties. Mendeleev's Periodic Table had only 63 elements whereas the Modern Periodic table have 109 elements.
In 1913 Sir Henry Moseley,an English Physicist discovered that
atomic number is the most fundamental property of an element and not it's
atomic mass. This discovery changed the whole perspective about elements and
their properties. Also the Mendeleev 's periodic law
was modified to Modern Periodic Law.
Modern Periodic Law :- The chemical and physical properties
of elements are the periodic function of their Atomic numbers. The Modern Periodic Table was
constructed based on the above law.
Features of the Modern Periodic Table :-
1)The elements in the periodic table are arranged in the
increasing order of their atomic number or electronic configurations .
2) The horizontal rows are called as "periods".
3) The vertical columns are called as " groups" .
4)The Modern periodic table consists of 7 periods and 18 groups.
PERIODS :-
a) Each period starts with an alkali metal and ends with an
inert gas element.
b) Elements present in the same period have same number of
shells which is equal to the
periodic number.
c) The 1st period is the shortest period containing only 2
elements i.e. Hydrogen (H)
& Helium (He). In this period, only the 1s orbital is filled.
d) The 2nd period contains 8 elements starting with Lithium (Li)
and ending with Neon (Ne). In
this period, the 2s & 2p orbitals are filled.
e) The 3rd period also contain 8 elements starting with Sodium
(Na) and ending with Argon (Ar).
In this period the 3s & 3p orbitals are filled.
f) The 4th period is the long period with 18 elements, starting
with Potassium (K) and ending
with Krypton (Kr). In this period, 4s & 4p and also the 3d orbitals are filled.
g) The 5th period is also the long period with 18 elements,
starting with Rubidium (Rb) and
ending with Xenon (Xe). The 5s & 5p along with 4d orbitals are filled.
h) The 6th period is the longest period with 32 elements. It not
only includes 10 elements
belonging to 5d series i.e. from Lanthanum (La) to Mercury (Hg) but also contains 14
elements belonging the 4f series called
lanthanides i.e from Cerium (Ce) to Lutetium (Lu). In this period, the 6s & 6p along with
the 4f & 5d orbitals are filled.
i) The 7th period is an incomplete period. It includes Fr along with the 14
elements belonging to 5f series called
actinides i.e from Thorium (Th) to Lawrencium (Lr). In this period, the 7s & 5f orbitals
are filled.
GROUPS :-
a) The Modern Periodic Table consists of 18 groups or vertical
columns.
b) Elements present in the same group show same physical and
chemical properties.
c) Also the elements present in the same group have same number
of electrons in the outermost
shell.
d) According to American convention, the groups are denoted by
roman numerals followed by either
an capital alphabet "A" if the group is in the s-block or p-block, or by
"B" if the group is in the d-block .
e) Thus the groups from 1 to 18 are denoted as IA , IIA, IIIB,
IVB, VB, VIB, VIIB, VIII, IB
,IIB, IIIA, IVA, VA, VIA, VIIA and 0 (zero).
f) The elements from IA to VII A group i.e the elements in the
groups 1, 2, 13, 14, 15, 16
& 17 are called as representative elements.
g) The 18th group or zero group elements are called as inert
gases or noble gases . This group
includes the elements He, Ne, Ar, Kr, Xe and Rn.
h) The elements in the groups from IIIB to IIB i.e., from group
3 to 12 are called as transition
elements .
i) The two rows placed at the bottom of the periodic table i.e
the Lanthanides and Actinides are
also considered to be the part of IIIB group
(i.e. group 3). These are usually called as inner transition elements .
The 14 elements with atomic number 58 to 71 are called as Lanthanides, whereas the 14
elements with atomic number 90 to 103 are called as Actinides.
Classification of Elements :-
At present elements upto atomic number 118 are known of which
the recently discovered elements are man-made. With such a large number of
elements,it is very difficult to study the chemistry of the individual elements
and the innumerable compounds they form.Hence it is necessary to classify the
elements for their systematic and organised studies. Therefore the Elements in
the Periodic Table are classified on the basis of their electronic configuration into 4 blocks
as s , p , d and f .
1. S-block :- The Group 1 and 2 elements contain 1 or 2 electrons in their outermost shell and are called
as s-block elements.
2. P-block :-The elements in the Groups from 13 to 17 and the 0 (zero )
group elements contain 3 to 8 electrons in their outermost shell and are called as p-block
elements.
3. D-block :- The elements in the Groups from 3 to
12 contain 1 to 2 electrons in
their outermost shell and are called as Transition elements. They are all metals.
4. F-block :- The 14 elements with atomic number 58
to 71 are called as Lanthanides
whereas the 14 elements with atomic number 90 to 103 are called as Actinides.These 28
elements are collectively called as f-block
elements.
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