what is the difference between these 2 paarraa
Answers
The two paragraphs show the problems arising from classification of elements in increasing order of atomic mass.
First of all :
What is classification of elements ?
Classification of elements means grouping of elements so that we can easily identify and remember the properties of elements which will increase periodically .
What do u mean by periodically ?
Periodically means increase in equal intervals of time ( or any other division of 2D ).
Example : Suppose in the Modern Periodic Table , the number of valence electrons increase by one for every one place you go from left to right.
This way you can easily identify the next element's valence electrons.
Thus periodicity means increase or decrease or Change in properties in equal respect !
Now if elements are arranged in increasing order of atomic mass then there arises several problems :
The first para says that we cannot predict the undiscovered elements.
By this what do we mean ?
If the elements were arranged periodically we can easily identify the properties of undiscovered elements.
For example : Hydrogen , lithium .....
After lithium , we can easily identify that the element will have 3 shells.
As hydrogen has 1 shell .
Lithium has 2 shells .
The number of shells are increasing by one and hence this is called periodicity.
If elements are arranged in the increasing order of atomic mass , then the properties of elements are not periodic and cannot be identified .
The undiscovered elements cannot be deciphered or predicted.
Suppose :
A has 4 grams .
B has 96 grams .
C has 100000 grams .
The atomic mass is not at all periodic .
Look at this now :
H = 1
L = 2
Na = 3
This is periodic because the next can be predicted .
The next K will be 4 .
Now the second para says " Hi ".
The atomic mass of elements should increase as we go further .
A = 1
B = 4
C = 7
D = 78
Now if D was placed before A :
D = 78
A = 1
B = 4
C = 7
Will it be proper classification ?
Answer is NO :
Thus the atomic mass is not periodic property as it cannot classify the elements .
Examples are given in the book .
I am not better than the book +__+
That the atoms cannot be arranged in increasing order of atomic mass.
If arranged there will be several problems and those are described in paras.
HOPE IT HELPS