Question

How does the valency,atomic size , metallic and non metallic properties vary down the group and across periods ?

Answer 1

Valency remains constant downwards in a group.However atomic size increases due to addition of new shells.The nuclear charge between the nucleus and the valence electron/s decrease.Henceforth the elements as going down the group gain tendency to loose electrons.This is known as electropositivity.Metals are electropositive.

Valency increases across a period.So the atomic radius decreases due to addition of new electrons which increased nuclear charge.Therefore the element gains tendency to gain electrons.This is known as electronegativity.Non metals are electronegative.

Answer 2

ANSWER:

1. Valency-

• The valency of an element is dependent on the number of electrons in the outermost shell of the electron.  
• In a group all constituting elements will have the same valency because they all have the same number of electrons in the outer shells.
• Across the a period, the number however increase by 1. Therefore in group 1 is valency of 1, in two valency of 2, and so on.

2. Atomic Size-

• Atomic size is the distance between the center of nucleus and the outermost electron in the outer shell.
• Across a period from left to right there is decrease in atomic size with increase in nuclear charge of the element.
• Atomic size increases down the group because of addition of extra shell.

3. Metallic and Non-Metallic Properties -

• Metallic character refers to the level of reactivity of a metal. Non-metallic character relates to the tendency to accept electrons during chemical reactions.
• Metallic tendency increases going down a group.
• Non-metallic tendency increases going from left to right across the periodic table.

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