Chapter 3 Periodic Table – 9th Class Chemistry Notes

Chapter 3 Periodic Table 9th Class Chemistry Notes

Question#1: Define Periodic table? What is the importance of periodic table?

Answer: Periodic Table:- Periodic table is the arrangement of elements in order of increasing atomic number in such a way that those with similar properties are placed one above other in the form of a table.

OR

Periodic table is the arrangement of elements in the form of a table in which elements with similar properties are placed in the same group.

Importance of periodic table: – The periodic table is the road map to elements. It tells us about atomic numbers, atomic masses, electronegativity, chemical properties as well as the relationship among various elements.

Question#2) Write a note on old forms of periodic table?      Or

Write a note on Dobereiner, Newland and Mendeleev’s periodic tables?

Dobereiners Triads: – A German chemist Doberneiner observed the relationship between atomic masses of several groups of three elements in which the central or middle element had atomic mass average of the other two elements.

 

Newlands Octaves; –  In 1984, Newland put forward his observations in the form of law of octaves. According to this law “there is a repetition in chemical properties of every eight element if they are arranged by increasing their atomic masses”.

 

Li      Be      B      C      N      O      F

7       9       11     12      14     16      19

 

Na     Mg      Al     Si      P       S      Cl

23      24      27     28      31      32     35.5

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