Question
Write down the outermost electronic configuration of alkali metals. How will you justify their placement in group 1 of the periodic table?
✓
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.
$_{11}\text{Na}-1\text{s}^2\ 2\text{s}^2\ 2\text{p}^6\ 3\text{s}^1\ \text{or }\big[\text{Ne}\big]3\text{s}^1$
$_{19}\text{K}-1\text{s}^2\ 2\text{s}^2\ 2\text{p}^6\ 3\text{s}^2\ 3\text{p}^6\ 4\text{s}^1\ \text{or } \big[\text{Ar}\big]4\text{s}^1$
$_{37}\text{Rb}-1\text{s}^2\ 2\text{s}^2\ 2\text{p}^6\ 3\text{s}^1\ 3\text{p}^6\ 3\text{d}^{10}\ 4\text{s}^2\ 4\text{p}^6\ 5\text{s}^1\ \text{or }\big[\text{Kr}\big]5\text{s}^1$
$_{55}\text{Cs}-1\text{s}^2\ 2\text{s}^2\ 2\text{p}^6\ 3\text{s}^1\ 3\text{p}^6\ 3\text{d}^{10}\ 4\text{s}^2\ 4\text{p}^6\ 4\text{d}^{10}\ 5\text{s}^2\ 5\text{s}^2\ 5\text{p}^6\ 6\text{s}^1\text{ or }\big[\text{Xe}\big]6\text{s}^1$
$_{87}\text{Fr}-\big[\text{Rn}\big]7\text{s}^1$
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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