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P-1 Periodic Classification of Element — Science STD 10 — Question

Maharashtra BoardEnglish MediumSTD 10ScienceP-1 Periodic Classification of Element3 Marks
Question
Halogens or group 17 elements.
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Answer

(i) The second last column in the periodic table is group 17 (VII – A) which contains halogens.
(ii) The members of this group from top to bottom are as given in the following table:
Group 17 elementsSymbolAtomic Number (Z)Electronic configurationValency
FluorineF92, 71
ChlorineCl172, 8, 71
BromineBr352, 8, 18, 71
IodineI532, 8, 18, 18, 71
AstatineAt852, 8, 18, 32, 18, 71
(iii) The valence shell of a halogen contains seven electrons.
(iv) Thus, it needs one electron to complete its octet.
(v) The halogen complete their octet and attain the stable inert gas configuration by gaining one electron.
(vi) Hence, the valency of halogens is one, i.e. they are monovalent
(vii) All of them have general formula $X_2$. Fluorine $\left( F _2\right)$ and Chlorine $\left( Cl _2\right)$ are gases. Bromine $\left( Br _2\right)$ is liquid while Iodine $\left(I_2\right)$ is solid.

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