THE PERIODIC TABLE
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Total number of elements discovered so far
118
The scientist who arranged the elements in increasing order of ATOMIC NUMBER
HENRY MOSELEY
What is a TRIAD?
Group of three elements
Which type of elements are shown at the bottom of the PT?
Inner transition elements OR Lanthanides and Actinides series
Find the odd one out. Dobereiner’s triad, Newland’s law of octaves, Mendeleev’s PT, Modern PT
Modern PT
A, B, C are the elements of a Dobereiner’s triad. If the atomic mass of A is 40 and that of C is 137, what should be the atomic mass of B?
88.5
Lithium, Sodium and Potassium elements were put in one group on the basis of their similar properties. What are those similar properties?
All are metals, Each has valency 1, Each has an oxide that is alkaline in nature
According to Newland’s law of octaves, there is resemblance in properties of FIRST element with _______ element when they are arranged in increasing order of atomic mass.
EIGHTH
What are periodic properties?
Properties which repeat themselves at regular intervals
Define Mendeleev’s periodic law
Physical and chemical properties of elements are periodic functions of their ATOMIC MASS
Name eka-boron
Scandium
Name eka- aluminium
Gallium
Name eka-silicon
Germanium
Explain the defect ANOMALOUS PAIRS OF ELEMENTS in Mendeleev’s PT. Give an example.
Certain pairs of elements having higher atomic masses have been given positions before the elements having lower atomic masses. Example: Co and Ni, Te and I
How can we overcome the defect ANOMALOUS PAIRS OF ELEMENTS in Mendeleev’s PT?
If we arrange elements according to their ATOMIC NUMBER
In Mendeleev’s PT the isotopes should be arranged in different positions. Why?
Because in Mendeleev’s PT, the elements are arranged in the increasing order of their atomic masses. Since isotopes have different atomic masses they should be arranged in different positions
Reason for periodicity in properties of elements.
Recurrenceof similar electronic configuration
Define modern periodic law
Physical and chemical properties of elements are periodic functions of their ATOMIC NUMBERS
Give 3 examples of periodic properties
Atomic radius, Ionisation potential, Electron affinity
Define atomic radius
distance between the centre of the nucleus and the outermost shell
Horizontal rows in Modern PT
Periods
Number of periods in MPT
7
Vertical columns in MPT
Groups
Number of Groups in MPT
18