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Periodic Classification of Elements — Science STD 10 — Question

CBSE BoardEnglish MediumSTD 10SciencePeriodic Classification of Elements2 Marks
Question
How does the elements having similar properties are placed in the same group or period?
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Answer

The chemical properties of elements are determined by their valence shell electronic configuration.
For example: The group 15 (nitrogen family),
The valence shell (outermost shell) electronic configuration of is $ns _2 np _3$, which clearly shows that all the elements have the tendency to make same kind if bonds with a common element. That is, consider the hydrates of the group, it is $NH _3$ (ammonia), $PH _3$ (phosphine), $AsH _3$ (arsine), $SbH _3$ (stibine) etc. They are having the same chemical formula and same type of bond (covalent bond) The physical properties include melting point, boiling point, density etc. Here for the same nitrogen family, all elements except nitrogen are solids in room temperature whereas nitrogen is gas. melting point (degree C ) is as shown below:
- $N :-209.86$
- P: 44.81
- As: 817
- Sb: 630.5
- Bi: 271.3

Here the physical properties shows a great variation. From the examples sighted above, even though the chemical properties exhibits almost same chemical properties, they doesn't follow same trend in physical properties.

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