CBSE Class 10 Science 2017 · Paper 31/3 · Question 10

Metals and Non-metals 3 marks Medium

Write the electronic configuration of two elements X and Y whose atomic numbers are 20 and 17 respectively. Write the molecular formula of the compound formed when element X reacts with element Y. Draw electron-dot structure of the product and also state the nature of the bond formed between both the elements.

Answer

X ( $2, 8, 8, 2$ ) and Y ( $2, 8, 7$ ) form the ionic compound $XY_{2}$ , $CaCl_{2}$ , by transfer of electrons.

Electronic configurations: X (atomic number 20) is

2, 8, 8, 2

(calcium); Y (atomic number 17) is

2, 8, 7

(chlorine). Formula of the compound:

XY_{2}

, that is,

CaCl_{2}

(X loses 2 electrons; each Y gains 1). Electron-dot structure: calcium transfers one electron to each of two chlorine atoms, forming

Ca^{2 +}

and two

Cl^{-}

ions, each chloride with eight electrons in its outer shell (see the figure). Nature of the bond: ionic (electrovalent) bond, formed by the transfer of electrons from X to Y.

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CBSE Class 10 Science 2017 · Paper 31/3 · Question 10

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