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Question

Give scientific reasons:

1. Atomic size increases down the group.

2. Metallic character decreases from left to right in a period.

3. Elements in the same group show same valency.

 


Solution

1. Atomic size is determined by atomic radius. On moving down the group, atomic size increases because of the addition of a new shell into the atom. This increases the distance between the outermost electrons and the nucleus so that the atomic size increases in spite of the nuclear charge.

For example, the Li atom which is present in the second period of the first group has two shells while Na which is present in the third period of the same group has four shells. Thus, atomic size of Na is greater than that of Li.

 

2. Metallic elements are electropositive in nature and have a tendency to lose electrons. It is easier to lose the outermost electron, which increases the metallic character. As we move from left to right in a period, the atomic size decreases (due to increased nuclear charge and increased attraction between nucleus and valence electrons). Therefore, the tendency to lose electrons decreases while the tendency to gain electrons increases. Hence, the metallic character decreases as we move from left to right in the table.

 

3. As valency is defined as the number of outermost electrons of an atom. A group contains same number of electrons in their outermost orbit. So, elements in the same group show same valency.

 


Science
Science & Technology
Standard X

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