Periodic Classification Of Elements PPT

Document Sample
Periodic Classification Of Elements PPT Powered By Docstoc
					Periodic Classification
     Of Elements
        Introduction To the
           periodic Table




There are 115 elements known at present. As it is difficult to study about all
of them, they have all been divided into some groups such that the same
group has similar properties. It is a chart of elements prepared in such a way
that elements having similar properties occur in the same vertical column or
group. It consists of horizontal rows of elements called periods and vertcal
columns called groups. This is known as the Periodic Table.
           Dobereiner’s Triads
Dobereiner was a German chemist who is best known
for work that foreshadowed the periodic law for
the chemical elements. He was the first scientist to
show the relation between the properties of elements
and their atomic masses. According to him when
elements are arranged in order of their increasing
atomic masses, groups of three elements, having
similar chemical properties are obtained. The atomic
mass of the middle element of the triad being equal
to the arithmetic mean of the atomic masses of the
other two elements.
               For example….
The elements lithium, sodium and potassium
have similar chemical properties and
form a triad. For example:
1.All these elements are metals.
2.All of them react with water to form
alkalis and hydrogen gas.
3.All of them have a         Elements of Symbols Atomic
valency of 1.                the Triad           Masses
Due to their similar
                             1. Lithium    Li      7
Properties, they were put 2. Sodium        Na      23
In one group called          3. Potassium  K       39
Alkali metal group.
     Newland’s Law Of Octaves
John Alexander Reina Newlands was an English
chemist who invented the Periodic Table.
According to him When elements are arranged
in the order of increasing atomic masses, the
properties of the eight element are a repetition
of the properties of the first element. He also
thought that the repetition of the eighth
element was like the repetition of the eighth
note in an octave of music, so it was known as
the law of octaves.
Newland divided the elements into horizontal rows
of seven elements each as shown below. His
classification gave a very important conclusion that
there is some systematic relationship between the
order of atomic masses and repetition of
properties of elements.



        H           Li   Be   B           C    N    O
        F           Na   Mg   Al          Si   P    S
        Cl          K    Ca   Cr          Ti   Mn   Fe
        CO and Ni   Cu   Zn   Y           In   As   Se
        Br          Rb   Sr   Ce and La   Zr   _    _
Newlands law of octaves has some limitations as given
below:
1. His law of octaves was applicable to the classification
of elements up to Calcium only. After Calcium every
eighth element did not posses similar properties.
2. He assumed that there were only 56 elements in
nature and no more would be discovered in future.
3. In order to fit the elements into his table, he even put
two elements together in one slot and that too in the
column of unlike elements having very different
properties.
4. Iron element which resembles cobalt and nickel
elements in properties was placed far away from them.
Mendeleev’s Periodic Table
Dmitri Ivanovo Mendeleev, was a Russian chemist
and inventor. He is credited as being the creator of
the first version of the periodic table of elements.
Using the table, he predicted the properties of
elements yet to be discovered. According to him
when elements are arranged in the order of
increasing atomic masses the elements with
similar properties occur at regular intervals. The
properties of elements are a periodic function of
their atomic masses. There were seven periods
and eighth groups in the original periodic table of
Mendeleev.
 Merits Of Mendeleev’s Periodic Table
The merits are:
1. Mendeleev’s periodic law predicted the
existence of some elements that had not been
discovered at that time.
2. Mendeleev’s periodic table could predict the
properties of several elements on the basis of
their positions in the periodic table.
3. Mendeleev’s periodic table could accommodate
noble gases when they were discovered.
 Limitation On The Periodic Table
The limitations are:
1. The positions of isotopes could not be
explained.
2. Wrong order of atomic masses of some
elements could not be explained.
3. A correct position could not be assigned o
Hydrogen in the periodic table.
 Trends In Modern Periodic Table




Valency: The number of valence electrons
is known as the valency of the element.
Atomic Size: Atomic size refers to the
radius of an atom.
Thank You
            Made By:
            Sakshi Jain
            Radhika Kumar
            Ashira Singh

				
DOCUMENT INFO
Shared By:
Tags: hahah
Stats:
views:640
posted:3/28/2012
language:English
pages:12
Description: Copyrights (C) Ashira Singh:P