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Chemistry

Five atoms are labelled V to Z

AtomsMass NumberAtomic Number
V4020
W199
X73
Y168
Z2814

(i) Which one of these atoms has an electronic configuration 2, 7? (2) has an electronic configuration 2, 7 ?

(ii) Write down the formula of the compound formed by atoms X and Y.

Atomic Structure

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Answer

(i) Electronic configuration 2, 7 means the atom has 2 + 7 = 9 electrons. Therefore, W has electronic configuration 2, 7 since its atomic number is 9.

(ii) Number of electrons in X is 3. Therefore, electronic configuration = 2, 1. X loses 1 electron to attain a stable duplet; hence, X has valency 1+.

Number of electrons in Y is 8. Therefore, electronic configuration = 2, 6.

Y gains 2 electrons to attain a stable octet; hence, Y has valency 2-.

Since valency of X is 1+ and valency of Y is 2-, the formula of the compound is:

X1+Y2X11  Y2X22  Y1\text{X}^{1+} \phantom{\nearrow} \text{Y}^{2-} \\[0.5em] \overset{\phantom{1}{1}}{\text{X}} \space {\searrow}\mathllap{\swarrow} \space \overset{2}{\text{Y}} \Rightarrow \underset{\phantom{2}{2}}{\text{X}} \space {\searrow}\mathllap{\swarrow} \space \underset{1}{\text{Y}} \\[0.5em]

So, the formula is X2Y\bold{X}_2\bold{Y}

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