Q17 of 31 Page 198

Why was the basis of classification of elements changed from the atomic mass to the atomic number?

The basis of classification of elements changed from the atomic mass to the atomic number is:


i. Certain elements of height atomic weight precede those with lower atomic weights.


For example: tellurium precedes iodine


ii. After knowing atomic numbers of elements, it was recognized that a better way of arranging the elements in the periodic table is according to increasing g atomic number.


iii. The periodic law is changed from atomic weight concepts to atomic number concepts.


More from this chapter

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15

In period 2, element X is to the right of element Y. Then, find which of the elements have:

(i) Low nuclear charge


(ii) Low atomic size


(iii) High ionization energy


(iv) High electro negativity


(v) More metallic character

 16

How does metallic character change when we move

(I) Down a group


(II) Across a period?

 18

What is a periodic property? How do the following properties change in a group and period? Explain.

(a) Atomic radius


(b) Ionization energy


(c) Electron affinity


(d) Electro negativity.


(b) Explain the ionization energy order in the following sets of elements:


a) Na, Al, Cl b) Li, Be, B


c) C N, O d) F, Ne, Na c) Be, Mg, Ca

 19

Name two elements that you would expect to have chemical properties similar to Mg. What is the basis for your choice?