Chapter 11, Problem 35A

Interpretation Introduction

Interpretation: Orbital that is first filled in an atom is to be determined.

Concept introduction: 3-D space around nucleus in which probability of finding an electron of particular energy is maximum, is called orbital. Quantum numbers are group of 4 numbers which tell everything about electron present in an atom. Principal quantum numbers indicates principal energy level in which electron in present. It is denoted by $n$ .

Answer to Problem 35A

In an atom, electrons are filled in lower energy orbitals that are closer to nucleus before they are filled in higher energy ones.

Explanation of Solution

As per Aufbau’s rule electrons are filled in lower energy orbitals that are closer to nucleus before they are filled in higher energy ones. The order of orbital arranged in their increasing energies is as follows:

  $\begin{array}{l}1s<2s<2p<3s<3p<4s<3d<4p<5s<4d<5p<\\ 6s<4f<5d<6p<7s<5f<6d<7p\end{array}$ .

Higher orbital are indicated by higher $n$ value prefixed to symbol of orbital. That is among $1s$ and $2s$ , $2s$ has higher energy value.

Also while filling of electrons, in a principal energy level $\left(n+1\right)s$ orbital is always filled before $nd$ orbital. That is in $n=3$ shell, $\left(n+1\right)s$ which is $4s$ is filled before $nd$ which is $3d$ orbital.

Conclusion

In an atom, electrons are filled in lower energy orbitals that are closer to nucleus before they are filled in higher energy ones.