Problem 29 - Chemistry and Chemical Reactivity

Question

A possible excited state of the H atom has the electron in a \(4 p\) orbital. List all possible sets of quantum numbers \(n, \ell,\) and \(m_{\ell}\) for this electron.

Step-by-Step Solution

Answer

The possible sets are: \( (4, 1, -1), (4, 1, 0), (4, 1, 1) \).

Step 1: Identify Quantum Numbers

Understand and identify the quantum numbers needed. The principal quantum number for the given orbital is \(n = 4\), and since it's a \(4p\) orbital, the azimuthal quantum number \(\ell\) is 1. This leaves us to determine the magnetic quantum number \(m_\ell\).

Step 2: Set Value of Principal Quantum Number

For the \(4p\) orbital, the principal quantum number is: \(n = 4\). This value indicates the energy level of the H atom's electron.

Step 3: Determine Azimuthal Quantum Number

For a \(p\) orbital, the azimuthal quantum number \(\ell\) is \(1\). This determines the shape of the orbital.

Step 4: Determine Magnetic Quantum Numbers

The magnetic quantum number \(m_\ell\) can take values from \(-\ell\) to \(\ell\). Therefore, for \(\ell = 1\), \(m_\ell\) can be \(-1, 0, \) or \(1\).

Step 5: List All Possible Sets of Quantum Numbers

Combine the quantum numbers to list the possible sets: 1. \(n=4, \ell=1, m_\ell=-1\)2. \(n=4, \ell=1, m_\ell=0\)3. \(n=4, \ell=1, m_\ell=1\)

Key Concepts

Principal Quantum Number

The principal quantum number, represented as \( n \), plays a crucial role in quantum mechanics. It signifies the main energy level occupied by an electron within an atom. Think of \( n \) as the floor number in a high-rise building, where each floor represents a different energy level.
For the given \( 4p \) orbital, the principal quantum number is \( n = 4 \). This indicates that the electron resides in the fourth energy level. The larger the value of \( n \), the higher the energy level and the further the electron is from the nucleus.
Here are a few things to remember about \( n \):

• It can take any positive integer value (e.g., 1, 2, 3, ...).
• The energy the electron possesses increases as \( n \) increases.
• The average distance from the nucleus also increases with \( n \).

Understanding \( n \) helps us comprehend how electrons are distributed within an atom's shells.

Azimuthal Quantum Number

The azimuthal quantum number, denoted by \( \ell \), tells us the shape of the orbital, and thus the subshell the electron is in. Imagine different orbitals as variously shaped rooms on the same floor of a building.
In the quantum world, \( \ell \) takes on values from 0 up to \( n-1 \) for any given principal quantum number \( n \). For a \( 4p \) orbital, \( \ell \) equals 1. This corresponds specifically to a "p" orbital, known for its dumbbell shape.
Here's a quick guide to \( \ell \) values and their respective shapes:

• \( \ell = 0 \): "s" orbital, spherical shape.
• \( \ell = 1 \): "p" orbitals, dumbbell shapes.
• \( \ell = 2 \): "d" orbitals, complex shapes.

By understanding \( \ell \), we grasp how the electron cloud is oriented around the nucleus.

Magnetic Quantum Number

The magnetic quantum number, symbolized as \( m_\ell \), specifies the orientation of an orbital in space. Think of it as determining which direction the room on each floor faces.
For a subshell labeled by \( \ell \), \( m_\ell \) ranges from \( -\ell \) to \( +\ell \). In the case of a \( 4p \) orbital where \( \ell = 1 \), \( m_\ell \) can be \(-1, 0, \) or \(1\). These values align the electron orbital around three possible orientations.
Some key points about \( m_\ell \):

• It describes how orbitals are directed within a magnetic field.
• Each orientation corresponds to a distinct spatial arrangement of the electron cloud.
• This orientation influences the way atoms bond chemically.

By knowing \( m_\ell \), we understand how electrons occupy their unique positions in an atom's structure.