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What is Diamagnetism (Molecular Orbital Theory)?
Grade Level:
Class 12
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Definition
What is it?
Diamagnetism is a property of materials that are weakly repelled by a magnetic field. According to Molecular Orbital Theory (MOT), this happens when all electrons in an atom or molecule are paired up, meaning there are no unpaired electrons to interact strongly with an external magnetic field.
Simple Example
Quick Example
Imagine you have a full bus with every seat taken by two friends sitting together. There are no empty seats, and no one is sitting alone. If a new passenger (like a magnetic field) tries to push someone around, it's very hard because everyone is already paired up and stable. This bus is like a diamagnetic substance, weakly resisting the new passenger.
Worked Example
Step-by-Step
Let's check if the Nitrogen molecule (N2) is diamagnetic using Molecular Orbital Theory (MOT).
Step 1: Find the total number of electrons in N2. Nitrogen (N) has 7 electrons. So, N2 has 7 + 7 = 14 electrons.
Step 2: Fill the molecular orbitals according to MOT rules for diatomic molecules with 14 or fewer electrons. The order is: sigma1s, sigma*1s, sigma2s, sigma*2s, pi2p, sigma2p.
Step 3: Place the 14 electrons into these orbitals, filling two electrons per orbital (one spin up, one spin down).
--- sigma1s: 2 electrons (paired)
--- sigma*1s: 2 electrons (paired)
--- sigma2s: 2 electrons (paired)
--- sigma*2s: 2 electrons (paired)
--- pi2p: 4 electrons (2 paired in one pi orbital, 2 paired in the other pi orbital)
--- sigma2p: 2 electrons (paired)
Step 4: Count the number of unpaired electrons. In N2, all 14 electrons are in pairs. There are no unpaired electrons.
Step 5: Conclude based on unpaired electrons. Since N2 has no unpaired electrons, it is diamagnetic.
Answer: N2 is diamagnetic.
Why It Matters
Understanding diamagnetism helps scientists design materials for advanced technologies. For example, in MRI machines used in medicine, diamagnetic properties are considered. It's also important in developing superconductors for faster trains and more efficient energy grids, impacting careers in medical imaging, materials science, and electrical engineering.
Common Mistakes
MISTAKE: Thinking diamagnetic substances are attracted to magnets. | CORRECTION: Diamagnetic substances are actually weakly REPELLED by a magnetic field.
MISTAKE: Confusing diamagnetism with paramagnetism. | CORRECTION: Diamagnetism means ALL electrons are paired, while paramagnetism means there are UNPAIRED electrons.
MISTAKE: Not considering the total number of electrons when applying MOT. | CORRECTION: Always calculate the total number of electrons in the molecule first to correctly fill the molecular orbitals.
Practice Questions
Try It Yourself
QUESTION: Is a Helium atom (He) diamagnetic or paramagnetic? (He has 2 electrons) | ANSWER: Diamagnetic (Both electrons are paired in the 1s orbital).
QUESTION: The molecule F2 has 18 electrons. Using MOT, determine if it is diamagnetic. | ANSWER: Yes, F2 is diamagnetic. All 18 electrons are paired in its molecular orbitals.
QUESTION: An unknown molecule 'X' has 10 electrons. After filling its molecular orbitals, it is found to have two unpaired electrons. Is 'X' diamagnetic or paramagnetic? Explain. | ANSWER: 'X' is paramagnetic because it has unpaired electrons.
MCQ
Quick Quiz
Which of the following conditions must be true for a substance to be diamagnetic according to Molecular Orbital Theory?
It must have an odd number of electrons.
It must have at least one unpaired electron.
All its electrons must be paired.
It must be a metal.
The Correct Answer Is:
C
Diamagnetism occurs when all electrons in a molecule or atom are paired up, leading to a weak repulsion from a magnetic field. Unpaired electrons lead to paramagnetism.
Real World Connection
In the Real World
You might not see diamagnetism every day, but it's crucial in advanced tech. For instance, in 'maglev' trains, powerful magnets are used for levitation. While these primarily use strong magnetic fields, understanding how materials like water (which is diamagnetic) interact with these fields is key for engineers at organizations like ISRO who work with precise magnetic environments for satellite components.
Key Vocabulary
Key Terms
DIAMAGNETISM: Weak repulsion by a magnetic field | MOLECULAR ORBITAL THEORY (MOT): A theory explaining how atomic orbitals combine to form molecular orbitals | UNPAIRED ELECTRON: A single electron occupying an orbital | PAIRED ELECTRON: Two electrons with opposite spins occupying the same orbital | MAGNETIC FIELD: A region around a magnetic material or a moving electric charge within which the force of magnetism acts.
What's Next
What to Learn Next
Next, you should learn about Paramagnetism and Ferromagnetism. These concepts build on understanding electron pairing and will help you differentiate between how different materials behave in magnetic fields, which is super useful for understanding many technologies around us.
