Classification of some elements.

1. PERIODIC CLASSIFICATION OF
ELEMENTS
1. Doberiners Traids(1875)
 Elements with similar properties were arranged into of three elements
called traids.
 He could identify only three traids from the element known.
2. Newlands’ law of octaves(1866).
 Elements were arranged in the order of increasing atomic masses
such that properties of eight elements was the repetation of the
properties of first element.
 This law worked well with lighter elements only.

2. 3. Mendeleev’s periodic Table (1869)
state that the properties of element are the periodic function of
their atomic masses.
Achievements
Accommodated nobel gases which were discovered late.
Some gaps were left to accommodate elements to be discovered later.
Limitations.
Could not assign a correct position to hydrogen
Position of isotopes could not be explained.
Wrong order of atomic masses of some elements could not be explained.

3. 4. Henry Moseley(1913).
showed that anomalies in arrangement of elements could be removed
when the elements were arrangement in order of increasing atomic
number.
• Characteristics of modern periodic table.
States that the properties of elements are periodic function of their
atomic number.
Consists of 18 vertical columns called group.
Consists of 7 horizontal rows called periods.
Atoms of different elements with same number of occupied outer
shells are placed in same period.
Position of an elements tell us about its chemical properties.

4. Trends in Modern Periodic Table
Across the period. Down the group.
Atomic size
Valency
Metallic character or electro positive
radical
Non metallic character or
electronegative radical
Decreases
First increase from 1 to 4 and then
decrease to 0.
decrease
Increases
Increases
Remain same.
Increases
Decreases