Position of Elements in Modern Periodic Table Video Lecture - Class 10

dear you will learn about the modern
periodic table in 1913 Henry mostly
showed that the atomic number of an
element is a more fundamental property
than its atomic mass so Mendeleev x'
periodic law was modified and atomic
number was adopted as the basis of the
modern periodic table the modern
periodic law is stated as properties of
elements are a periodic function of the
an atomic number atomic number is the
number of protons in an atom and it
increases by one unit in going from one
element to the next elements when
arranged in order of increasing atomic
number lead us to the classification
known as the modern periodic table the
properties of elements could be
predicted with more precision when
elements were arranged on the basis of
increasing atomic number for example the
sodium atom contains eleven protons and
11 electrons therefore the atomic number
of sodium is eleven similarly the atomic
number of magnesium is twelve since the
atomic number of magnesium is higher
than that of sodium magnesium is placed
after sodium in the modern periodic
table let's examine the feet
of the table elements are arranged in an
increasing order of their atomic numbers
horizontal rows in the periodic table
are called periods and vertical columns
in the table are called groups elements
in the modern periodic table are
arranged in seven periods and 18 groups
you can locate an element in the
periodic table by referring to the
relevant period and group for example
the elements present in Group one of the
periodic table are lithium sodium
potassium rubidium cesium and francium
the electronic configuration of lithium
is 2:1 sodium is to 8:1 and potassium is
to eight eight one all these elements
contain the same number of valence
electrons valence electrons are the
electrons present in the outermost shell
hence we can conclude that the elements
present in a group will have the same
number of valence electrons let us take
the example of fluorine and chlorine
which belong to group 17 in the periodic
table the electronic configuration of
fluorine is 2:7 and chlorine is 2 8 7
both of them have the same number of
valence electrons hence we can say that
the groups in the periodic table signify
an identical outer shell electronic
configuration the number of shells also
increases as we go down the group there
is an anomaly when it comes to the
position of hydrogen in the periodic
table as it can be placed either in
Group 1 or group 17 of the first period
like alkali metals hydrogen combines
with oxygen sulfur and halogens to form
similar compounds on the other hand like
halogens hydrogen exists as a diatomic
molecule and combines with metals and
nonmetals to form covalent compounds
when we look at the long form of
periodic table we find that the elements
lithium beryllium boron carbon nitrogen
oxygen fluorine and neon are present in
the second period the electronic
configuration of lithium is 2 1
beryllium is 2 2 boron is 2 3 carbon is
2 4 and so on we can see the
these elements do not have the same
number of valence electrons but they
have the same number of shells the
number of valence electrons increases by
one unit as the atomic number increases
by one unit on moving from left to right
in a period the position of elements in
groups depends on the number of valence
electrons in an atom the atoms of
different elements with the same number
of occupied shells belong to the same
period for example sodium magnesium
aluminium silicon phosphorus sulfur
chlorine and argon belong to the third
period of the modern periodic table
since the electrons in these atoms of
elements are filled in the K L M
the electronic configuration of sodium
is to 8:1 and magnesium is to 8 - in
each period a new electronic shell gets
filled let us see how many elements are
present in different periods for example
1st 2nd 3rd and 4th periods this can be
explained on the basis of how many
electrons are filled in various shells
we know that the maximum number of
electrons that can be accommodated in a
shell is given by 2 n raised to the
power of 2 where n is the number of the
given shell from the nucleus
for example k shell is equal to 2
multiplied by 1 raised to the power of 2
is equal to 2 hence the first period has
two elements that is hydrogen and helium
L shell is equal to 2 multiplied by 2
raised to the power of 2 is equal to 8
hence the second period has 8 elements
that is lithium beryllium boron carbon
nitrogen oxygen fluorine and neon M
shell is equal to 2 x 3 raised to the
power of 2 which is equal to 18
but the outermost shell can have only 8
electrons so the third period has only 8
elements that is sodium magnesium
aluminium silicon
phosphorus sulfur chlorine and argon if
you begin with Group one the position of
an element in the periodic table tells
us about the chemical reactivity the
elements present in the same group will
have similar properties as they have the
same number of valence electrons valence
electrons determine the kind and number
of bonds formed by the element in this
module you have learnt that the modern
periodic law is stated as properties of
elements are a periodic function of
their atomic number elements are
arranged in an increasing order of their
atomic numbers valence electrons are the
electrons present in the outermost shell
the elements present in a group will
have the same number of valence
electrons groups in the periodic table
signify an identical outer shell
electronic configuration the position of
elements in groups depends on the number
of valence electrons in an atom