Quantum Numbers and Electronic Configuration in Chemistry
by Yuvi K - December 16, 2023
Quantum Numbers in Chemistry: Exploring Atoms and Electron Configurations
Chemistry is the fascinating study of matter and how it behaves. A key component of this science is understanding the building blocks of matter, atoms. Quantum numbers help to describe the atomic systems and note where electrons will be found within them. Keeping track of the electrons in each atom is important, as it helps to create the electronic configuration for the atom.
In this article, we discuss what quantum numbers are, how to identify them, and how they influence electron configuration. We also take a look at how quantum numbers affect the structure of an atom and explain their role in chemistry. Lastly, we will go over a few examples to carefully illustrate the concept. Let’s begin.
What are Quantum Numbers?
Quantum numbers (क्वांटम संख्याएँ) are numerical values that are used to describe the state and energy of a particle known as an electron. In atomic physics, the quantum numbers are used to describe the orbital chemical properties of an element. These numbers are expressed as whole numbers or fractions, but never as negative numbers.
Types of Quantum Numbers
There are four distinct types of quantum numbers: the principal quantum number (n), the angular momentum quantum number (l), the magnetic quantum number (m_l), and the spin quantum number (m_s).
Principal Quantum Number (n)
The principal quantum number (n) represents the electron’s energy level and is the most important of all the quantum numbers. It is represented by integer values of 1, 2, 3, 4, and so on. The higher the number, the greater the energy and the farther away the electron is from the nucleus.
Angular Momentum Quantum Number (l)
The angular momentum quantum number (l) describes the shape of the orbit of an electron in an atom. It is also known as the orbital quantum number and is represented by the letters s, p, d, and f. Each letter corresponds to a number, with s being 0, p being 1, d being 2, and f being 3.
Magnetic Quantum Number (m_l)
The magnetic quantum number (m_l) is related to the angular momentum quantum number (l). It is used to specify the orbital (or orbitals) that an electron occupies and is represented by a number between negative l and positive l.
Spin Quantum Number (m_s)
The spin quantum number (m_s) describes the spin of the electron. In other words, it specifies which way the electron is spinning. It is either +1/2 or -1/2, representing spin up or spin down, respectively.
Electron Configuration
The electron configuration of an element is the arrangement of electrons in orbitals or shells around the nucleus.
It is useful for predicting how the element will react with other elements and is determined by the quantum numbers.
Table showing Quantum Numbers vs. Electronic Configuration
| Quantum Number | Orbital Foundation | Electronic Configuration |
|---|---|---|
| Principle Quantum Number (n) | Energy level | [Energy] 2, 8, 18, 32… |
| Angular Momentum Quantum Number (l) | Shape of the orbital | s,p,d,f |
| Magnetic Quantum Number (ml) | Orientation of the orbital | -l → 0 → +l |
| Spin Quantum Number (ms) | Spin of the electron in the orbital | +1/2 or -1/2 |
Quantum Numbers and Atomic Structure
Now that we’ve discussed the different types of quantum numbers and how they’re used to determine electron configuration, let’s take a look at how they affect the structure of an atom.
The principal quantum number (n) helps to determine the size of an atom. This is because electrons with a higher n (i.e. greater energy) will be farther away from the nucleus than electrons with a lower n (i.e. lower energy).
The angular momentum quantum number (l) helps to determine the shape of the atom. This is because electrons with larger l values occupy larger orbitals. Therefore,s orbitals are spherical while p orbitals are dumbbell-shaped, d orbitals are double-lobed, and f orbitals are complex.
The magnetic quantum number (m_l) helps to determine the orientation of the orbitals. This is because the value of the m_l for an electron determines which orbital it occupies. The value of the m_l can range from -l to +l.
The spin quantum number (m_s) helps to determine the spin of the electron. This is because each electron in an orbital can have either a spin up or a spin down. Spin up electrons have a m_s of +1/2 and spin down electrons have a m_s of -1/2.
Examples of Quantum Numbers in Use
Let’s now consider a few examples of quantum numbers in use.
The first example is Sodium (Na). The electronic configuration of Sodium is [Ne]3s1. In this case, n = 3, l = 0 (s orbital), m_l = 0, and m_s = +1/2.
The second example is Chlorine (Cl). The electronic configuration of Chlorine is [He]2s22p6. In this case, n = 2, l = 0 (s orbital), m_l = 0, m_s = +1/2, and n = 3, l = 1 (p orbital), m_l = -1,0, +1, and m_s = -1/2.
The third example is Oxygen (O). The electronic configuration of Oxygen is [He]2s22p4. In this case, n = 2, l = 0 (s orbital), m_l = 0, m_s = +1/2, and n = 3, l = 1 (p orbital), m_l = -1,0, +1, and m_s = -1/2.
Conclusion
In summary, quantum numbers are numerical values that are used to describe the state and energy of an electron. There are four main quantum numbers: the principal quantum number, the angular momentum quantum number, the magnetic quantum number, and the spin quantum number. These quantum numbers help to determine the electron configuration of an element and the shape, size, and spin of the electrons in an atom. Examples of quantum numbers in action include Sodium, Chlorine, and Oxygen.
Hopefully, this article has given you a better understanding of how quantum numbers and electron configuration work and how they play a role in chemistry.
