Atomic No. |
Electronic Configuration |
\(\Bigg\{\begin{matrix}
13 \\
31
\end{matrix}\) |
2,8,3
2,8,18,3 |
\(\Bigg\{\begin{matrix}
11 \\
21
\end{matrix}\) |
2, 8,1
2,8,9,2 |
Since the elements having atomic number 13 and 31 have 3 outermost electrons. So, these elements are placed in 3rd group due to which these elements have similar properties.