Question

How many unpaired electrons are in a boron atom?

Answer 1

First of all we need to remind the point about paramagnetism property which states the presence of having unpaired electrons. So, to find unpaired electrons means , actually we need to find whether the given atom or compound is paramagnetic in nature which means having unpaired electrons. For calculating unpaired electrons, first of all we shall write the electronic configuration and further step is to find unpaired electrons from them.

Complete answer:
First of all we have to look into electronic configuration of Boron.
Boron is having atomic number $5$ which means it is having five electrons in its orbits. And here Boron is having three electrons in its outermost shell.
So let us write the electronic configuration of the Boron atom.
$1{s^2}2{s^2}2{p^1}$
Here we can see $s$ subshell is completely filled as $s$ subshell can accommodate two electrons in maximum and here also it is having two electrons.
But when we take the case of $p$ orbitals , it is only having one electron. Actually $p$ subshell will be completely filled when it accommodates six electrons as it is the maximum number of accommodations in case of $p$ subshell . But here it is having only one electron instead of six electrons.
Since here $2p$ subshell is not filled completely , it is paramagnetic in nature with one unpaired electron.
Hence boron atoms are having $1$ unpaired electrons.

Note: For dealing such questions , we have to know the atomic number as well as subshell electronic configuration of a particular element given. Then we need a clear idea about the maximum electron accommodation in subshells. If we know the maximum electron accommodation, we can easily find the unpaired electrons in it. But another point to keep in mind here is , when bonding takes place in compounds , one of $2s$ electron is promoted to $2p$ subshell and as a result $s{p^2}$ hybrid orbitals are formed and hence three bonding orbitals exist.