(solved)Question 3.27 of NCERT Class XI Chemistry Chapter 3

Use the periodic table to answer the following questions. (a) Identify an element with five electrons in the outer subshell. (b) Identify an element that would tend to lose two electrons. (c) Identify an element that would tend to gain two electrons. (d) Identify the group having metal, non-metal, liquid as well as gas at the room temperature.

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Parveen,

Question 3.27
NCERT Class XI Chemistry

Use the periodic table to answer the following questions. (a) Identify an element with five electrons in the outer subshell. (b) Identify an element that would tend to lose two electrons. (c) Identify an element that would tend to gain two electrons. (d) Identify the group having metal, non-metal, liquid as well as gas at the room temperature.

Solution in Detail
(video solution below this)

$\displaystyle \underline{\underline{\text{(a) 5 electrons in outer shell}}}$

Point 1: by aufbau diagram [see the video], (n - 1)d is filled only after ns is filled. Hence, d cannot be the outermost sub-shell. Similarly, (n - 2)f is filled only after (n - 1) d is filled. Hence f cannot be the outermost sub-shell. Therefore, only s or p can be outermost sub-shell. But s cannot have more than 2 electrons. Hence, we have to look for $\displaystyle np^5$ outermost sub-shell. Any element of G17 has the outermost configuration p5.

Point 2: we observe that $\displaystyle \text{[He]}2s^22p^5$ is the configuration of florine Z = 9

$\displaystyle \therefore F (\text{Z = 9} ) \underline{Ans} $

$\displaystyle \underline{\underline{\text{(b) element to lose 2 electrons}}}$

The outermost config should be [Noble Gas]ns^2 so that a noble gas configuration is achieved after losing 2 electrons!

Hence $\displaystyle \text{[He]}2s^2 \text{ or Z = 4, Be } \underline{Ans}$

$\displaystyle \underline{\underline{\text{(c) element to gain 2 electrons}}}$

Chalcogens G16 are 2 electrons away from Group 18 noble gases.

Hence $\displaystyle \text{O (Z = 8)} \underline{Ans}$

$\displaystyle \underline{\underline{\text{(d) non/metal, gas, liquid}}}$

Group I has hydrogen H as non-metal-cum-gas, Na as solid-cum-metal, Cs is a liquid at 28 degree C.

Another answer is Group 17 - Ts (tennessine) is a metal, Bromine a liquid, Chlorine a gas-cum-nonmetal.

Note: Ts was discovered later in 2010, so the probable answer at the time of the publication of NCERT book seems to be Group 1

Video Explanation

Please watch this youtube video for a quick explanation of the solution:

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