Which Of The Following Orbital Diagrams Represents A Diamagnetic Atom

Which of the following orbital diagrams represents a diamagnetic atom

Understanding whether an atom is diamagnetic or paramagnetic hinges on a single, straightforward fact: diamagnetic substances have all of their electrons paired, while paramagnetic substances possess at least one unpaired electron. Orbital diagrams provide a visual shorthand for the arrangement of electrons in an atom’s subshells, making it easy to spot unpaired spins. Below is a step‑by‑step guide to reading those diagrams, the underlying theory that connects electron pairing to magnetic behavior, and a worked‑through example that shows how to pick the correct diagram from a set of choices.

Introduction

When a material is placed in an external magnetic field, its response can be classified as diamagnetic, paramagnetic, or ferromagnetic. For isolated atoms, ferromagnetism does not occur; the distinction reduces to diamagnetism versus paramagnetism. Diamagnetic atoms are weakly repelled by magnetic fields because their electrons generate tiny magnetic moments that cancel each other out. Paramagnetic atoms, by contrast, are weakly attracted because unpaired electrons produce net magnetic moments that align with the field.

Because the magnetic behavior stems directly from electron spin, an orbital diagram—which shows each electron as an upward (↑) or downward (↓) arrow in a specific orbital—serves as a reliable diagnostic tool. If every arrow is paired with an opposite‑spin partner in the same orbital, the atom is diamagnetic. Any lone arrow signals paramagnetism.

Understanding Magnetism in Atoms

Electron Spin and Magnetic Moment

Each electron carries an intrinsic spin quantum number, s = ±½. This spin creates a magnetic dipole moment. When two electrons occupy the same orbital, the Pauli exclusion principle forces them to have opposite spins (↑↓). Their magnetic moments point in opposite directions and cancel, yielding a net contribution of zero to the atom’s overall magnetism.

If an orbital contains a single electron, its spin is unopposed, leaving a residual magnetic moment. The vector sum of all such unpaired moments determines whether the atom is attracted (paramagnetic) or repelled (diamagnetic) by an external field.

Hund’s Rule and Electron Filling

Hund’s rule states that electrons will fill degenerate orbitals (those with the same energy) singly before pairing up. This maximizes the number of unpaired electrons and, consequently, the paramagnetic character of an atom in its ground state. However, once all available orbitals in a subshell are singly occupied, any additional electrons must pair, reducing the number of unpaired spins.

Criteria for Diamagnetism from an Orbital Diagram 1. Every occupied orbital contains two arrows (one ↑, one ↓).

2. No orbital displays a solitary arrow.
3. All subshells are either completely empty or completely filled with paired electrons.

If any of these conditions fail, the atom is paramagnetic. Note that core electrons (those in filled inner shells) are always paired and therefore do not affect magnetic properties; the decisive factor lies in the valence (outermost) electrons.

How to Read an Orbital Diagram

An orbital diagram is typically drawn as a series of boxes (or lines) representing individual orbitals within a subshell. Each box can hold up to two arrows:

• ↑ denotes an electron with spin +½.
• ↓ denotes an electron with spin –½.

The diagram is read left‑to‑right, following the Aufbau principle (1s → 2s → 2p → 3s → 3p → 4s → 3d → …).

Example: The diagram for neon (Ne, Z = 10) looks like:

1s: ↑↓
2s: ↑↓
2p: ↑↓ ↑↓ ↑↓

All boxes contain paired arrows → neon is diamagnetic.

Worked‑Through Example: Identifying the Diamagnetic Diagram

Suppose a multiple‑choice question presents four orbital diagrams labeled A, B, C, and D for an element in the second period. The task is to select the diagram that corresponds to a diamagnetic atom. Below is a typical set of diagrams (described in words, as the original images are not provided) and the reasoning that leads to the correct answer.

Explanation:

• Diagram B shows every orbital completely filled with opposite‑spin electrons. No box contains a lone arrow, satisfying the diamagnetism criterion.
• Diagrams A, C, and D each display at least one unpaired electron, making them paramagnetic.

Therefore, the correct choice is B.

Common Pitfalls When Analyzing Orbital Diagrams

1. Confusing orbital boxes with subshell labels – Remember that each box represents a single orbital (e.g., one of the three 2p orbitals), not the entire subshell.
2. Overlooking inner‑shell electrons – While core electrons are always paired, it is easy to mistakenly count them as unpaired if the diagram is misaligned. Always verify that the diagram follows the Aufbau order.
3. Misapplying Hund’s rule – In the ground state, electrons occupy degenerate orbitals singly before pairing. An excited‑state diagram may show paired electrons in one orbital while another remains empty; such a configuration is not representative of the atom’s lowest‑energy state and may lead to an incorrect magnetic assignment if not noted.

Practical Applications and Verification of DiamagnetismWhile the theoretical framework for identifying diamagnetic atoms via paired electron configurations is fundamental, understanding diamagnetism extends beyond abstract diagrams into tangible phenomena. Diamagnetic materials, characterized by all electrons paired, exhibit a weak, repulsive response to external magnetic fields. This behavior arises because the induced magnetic moment opposes the applied field, a direct consequence of Lenz's law. Unlike paramagnetic materials, which are attracted to magnetic fields due to unpaired electron spins, diamagnetic substances are fundamentally non-magnetic under normal conditions.

In practical terms, this principle is observable in everyday materials. For instance, water (H₂O) and bismuth (Bi) are diamagnetic. Bismuth, the most strongly diamagnetic element, is used in precision instruments like superconducting magnets to create regions of zero magnetic field. Similarly, the diamagnetic repulsion of water can be demonstrated by levitating a frog in a strong magnetic field, a feat achieved using the powerful electromagnets at the High Field Magnetic Laboratory in the Netherlands. These applications highlight how the microscopic electron configuration dictates macroscopic magnetic properties.

Verifying Diamagnetic Configuration: A Checklist

To confidently identify a diamagnetic orbital diagram, apply this systematic approach:

1. Confirm Aufbau Order: Ensure the diagram follows the correct sequence (1s → 2s → 2p → 3s → 3p → 4s → 3d → ...). Deviations indicate excited states, not ground state diamagnetism.
2. Count Total Electrons: Verify the total number of electrons matches the atomic number (Z) of the element.
3. Analyze Each Orbital Box: Examine every orbital box (each represents a distinct spatial orbital).
   • Paired Arrows (↑↓): Indicates a filled orbital, contributing to diamagnetism.
   • Single Arrow (↑ or ↓): Indicates an unpaired electron, disqualifying diamagnetism.
4. Check for Lone Electrons: Scan the entire diagram. If any orbital contains a single arrow (↑ or ↓), the atom is paramagnetic. Only diagrams with zero unpaired electrons are diamagnetic.
5. Cross-Reference with Periodic Table: For elements in the second period (Li to Ne), the ground state configuration is well-established. A diagram showing unpaired electrons for elements like Boron (B, Z=5) or Carbon (C, Z=6) in their ground state is incorrect and cannot represent a diamagnetic atom.

Conclusion

The identification of diamagnetic atoms hinges on the fundamental principle that all electrons must be paired within their orbitals, as dictated by the Aufbau principle and Hund's rule in the ground state. Diagrams like the one for neon (Ne, Z=10) serve as clear exemplars, showcasing complete orbital filling with paired spins. Conversely, diagrams displaying any unpaired electrons (↑ or ↓ alone) immediately signal paramagnetism. While the examples provided focused on the second period, this principle applies universally across the periodic table. Mastery of orbital diagram analysis, avoiding common pitfalls like mislabeling boxes or overlooking inner shells, is crucial for accurately predicting magnetic behavior. The practical manifestations of diamagnetism, from levitating frogs to enabling superconducting magnets, underscore the profound connection between microscopic electron configurations and macroscopic physical properties, demonstrating the enduring relevance of this foundational concept in chemistry and physics.