# Question e453d

Jan 3, 2017

The arrangement of electrons in the orbitals of an atom or molecule.

#### Explanation:

So basically the electronic configuration tells us which element is present in which groups, in which periods and in which block (s block, p block, d block and f block).

By knowing how many electrons are present in the shells, we can find the place of an element in the periodic table.

Q: Find the electronic configuration of aluminium?

Ans: $\text{Al}$ has an atomic number equal to $13$

So,

$\frac{1 {s}^{2}}{\text{K" " " (2s^2,2p^6)/"L"" "(3s^2,3p^1)/"M}}$

Here "K#" is the first shell, $\text{L}$ is the second, and $\text{M}$ is the third shell (the valence shell).

As $n = 3$, $\text{Al}$ is present in the $\text{3rd}$ period. Since the total number of electrons in the valence sub-shells are

$2 + 1 = 3$

it must be present in group lllA (in Roman Numerals). or group 13. and in the last shell, we have a $\text{p}$ so we can say that aluminium is present in the p block.