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Classification of Elements and Periodicity in Properties — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistryClassification of Elements and Periodicity in Properties3 Marks
Question
Write down the outermost electronic configuration of alkali metals. How will you justify their placement in group 1 of the periodic table?
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Answer

$\text{Li}- 1\text{s}^22\text{s}^1\text{ or }\big[\text{He}\big]2\text{s}^1$
$_{11}\text{Na}-1\text{s}^2\ 2\text{s}^2\ 2\text{p}^6\ 3\text{s}^1\ \text{or }\big[\text{Ne}\big]3\text{s}^1$
$_{19}\text{K}-1\text{s}^2\ 2\text{s}^2\ 2\text{p}^6\ 3\text{s}^2\ 3\text{p}^6\ 4\text{s}^1\ \text{or } \big[\text{Ar}\big]4\text{s}^1$
$_{37}\text{Rb}-1\text{s}^2\ 2\text{s}^2\ 2\text{p}^6\ 3\text{s}^1\ 3\text{p}^6\ 3\text{d}^{10}\ 4\text{s}^2\ 4\text{p}^6\ 5\text{s}^1\ \text{or }\big[\text{Kr}\big]5\text{s}^1$
$_{55}\text{Cs}-1\text{s}^2\ 2\text{s}^2\ 2\text{p}^6\ 3\text{s}^1\ 3\text{p}^6\ 3\text{d}^{10}\ 4\text{s}^2\ 4\text{p}^6\ 4\text{d}^{10}\ 5\text{s}^2\ 5\text{s}^2\ 5\text{p}^6\ 6\text{s}^1\text{ or }\big[\text{Xe}\big]6\text{s}^1$
$_{87}\text{Fr}-\big[\text{Rn}\big]7\text{s}^1$
Since all the elements have one electron in their valence shell, hence, they are placed in first group of the periodic table.

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