2. Periodic Classification Of Elements
- Today 118 elements were known.
- Around year 1800 only about 30 elements are known.
• Doberainer’s Triads.
- A German scientist Doberainer suggested that properties of elements
are the periodic function of their atomic masses.
- He made groups of three elements each, having similar chemical
properties and called them triads.
- He arranged the thee elements in a triads in an increasing order of
atomic mass and showed that the atomic mass of the middle element
was approximately equal to the mean of the atomic masses of the
other two elements.
- All the elements could not be classified into the Doberainer triads.
• Newlands law of octaves.
- The English scientist John Newland correlated the atomic masses of
elements to their properties in a different way.
, - In the year 1866 Newlands arranged the elements known at that time
in an increasing order of their atomic masses.
- It started with the lightest element hydrogen and ended up with
thorium.
- He found that every eighth element had properties similar to those of
first.
Ex:- 1) sodium is the eighth element from lithium and both have similar
properties.
2) magnesium shows similarity to beryllium and chlorine shows similarity
with fluorine.
- He called the similarity observed in the eighth and the first element as
the Law of octaves.
- The law was found to be applicable only up to Calcium.
- Newland fitted all the known elements in a table of 7x8 that is 56
boxes.
- Newland placed two elements each in some boxes to accommodate all
the known elements in the table.
Ex :- Cobalt (Co) and Nickel (Ni), Ce and La.
2
- Today 118 elements were known.
- Around year 1800 only about 30 elements are known.
• Doberainer’s Triads.
- A German scientist Doberainer suggested that properties of elements
are the periodic function of their atomic masses.
- He made groups of three elements each, having similar chemical
properties and called them triads.
- He arranged the thee elements in a triads in an increasing order of
atomic mass and showed that the atomic mass of the middle element
was approximately equal to the mean of the atomic masses of the
other two elements.
- All the elements could not be classified into the Doberainer triads.
• Newlands law of octaves.
- The English scientist John Newland correlated the atomic masses of
elements to their properties in a different way.
, - In the year 1866 Newlands arranged the elements known at that time
in an increasing order of their atomic masses.
- It started with the lightest element hydrogen and ended up with
thorium.
- He found that every eighth element had properties similar to those of
first.
Ex:- 1) sodium is the eighth element from lithium and both have similar
properties.
2) magnesium shows similarity to beryllium and chlorine shows similarity
with fluorine.
- He called the similarity observed in the eighth and the first element as
the Law of octaves.
- The law was found to be applicable only up to Calcium.
- Newland fitted all the known elements in a table of 7x8 that is 56
boxes.
- Newland placed two elements each in some boxes to accommodate all
the known elements in the table.
Ex :- Cobalt (Co) and Nickel (Ni), Ce and La.
2
