a. Mendeleev's and the modern periodic table.
Mendeleev's | Modern |
It supported the first scientific study of elements. | It is the latest and standard table of elements. |
Elements were arranged with the increasing order of their atomic weight. | Elements were arranged with the increasing order of their atomic number.
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It had several gaps for undiscovered elements. | Most of the elements are discovered and arranged. |
It was unable to arrange isotopes. | It is able to arrange isotopes. |
It didn't have lanthanides and actinides series. | It consists of lanthanides and actinides series. |
b. Periods and groups.
Periods | Groups |
The horizontal rows in the periodic table are periods of the periodic table. | The vertical column in the periodic table are groups of the periodic table.
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The change in valency is found in a period. | The valency of elements remains the same in a group. |
A period contains the elements of different blocks. | A group contains the element of the same block. |
c. s-block elements and p-block elements.
s-block | p-block |
The last electron of these elements enters the s-orbital of the outermost shell. | The last electron of these elements enters the p-orbital of the outermost shell.
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These elements are alkali metals. | These elements are non-metals. |
These elements are electronically positive. i.e. they have positive valency. | These elements have negative valency.
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d. Alkali metals and halogens.
Alkali metals | Halogens |
These elements are highly reactive electro-positive metals. | These elements are highly reactive electro-negative metals. |
These elements are good conductors of electricity. | These elements are insulators of electricty. |
These elements have positive valency. | These elements have negative valency. |
e. Alkali metals and alkaline earth metals.
Alkali metals | Alkaline earth metals |
These elements are placed in group IA of the periodic table. | These elements are placed in group IIA of the periodic table. |
These elements are more reactive. | These elements are comparatively less reactive. |
These elements have valency +1. | These elements have valency +2. |
f. Duplet stable state and octet stable state.
Duplet stable | Octet stable |
The atom which has a stable electronic configuration having 2 electrons in its valance shell is duplet stable. | The atom which has a stable electronic configuration having 8 electrons in its valance shell is octet stable.
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This is possible only in 1st or 2nd shell. | This is possible in any shell of an atom. |