Briefly answer the following questions. (a) If positive and...

Name: Problem 1, Chapter 2: Elements of Solid State Physics
Uploaded: 2021-09-10T16:48:10-08:00
Duration: 1 min 2 s
Channel: Emily Himsel
Description: Briefly answer the following questions. (a) If positive and negative ions attract each other, why does the structure not collapse? (b) Why is it that the cohesive energy of an ionic crystal is almost equal to the attractive Coulomb energy? (c) What is the origin of cohesion in metals? Can it be described by interatomic potentials or covalent or any other bonds?

Briefly answer the following questions. (a) If positive and negative ions attract each other, why does the structure not collapse? (b) Why is it that the cohesive energy of an ionic crystal is almost equal to the attractive Coulomb energy? (c) What is the origin of cohesion in metals? Can it be described by interatomic potentials or covalent or any other bonds?

Briefly answer the following questions.
(a) If positive and negative ions attract each other, why does the structure not collapse?
(b) Why is it that the cohesive energy of an ionic crystal is almost equal to the attractive Coulomb energy?
(c) What is the origin of cohesion in metals? Can it be described by interatomic potentials or covalent or any other bonds?

Key Concepts

Cohesive Energy in Ionic Solids

The cohesive energy of ionic crystals is dominated by the attractive Coulomb energy, but it is fine-tuned by the short-range repulsive forces. The net binding energy, often summarized by a Madelung constant, shows that while repulsive interactions stabilize the structure, the overall cohesive energy remains nearly equal to the sum of the attractive Coulomb interactions.

Electrostatic (Coulomb) Interactions

In both ionic and metallic bonding, the long?range Coulomb forces between charged particles play a central role. In ionic crystals, the attractive force between oppositely charged ions is the primary energy contribution that holds the lattice together, while in metals the delocalized electrons mediate effective attractions between positively charged atomic cores.

Short?Range Repulsion and Overlap Effects

At very short distances, electron cloud overlaps lead to strong repulsive forces, largely due to the Pauli exclusion principle. In ionic crystals, this repulsion counterbalances the strong Coulomb attractions, establishing an optimal equilibrium spacing that prevents collapse of the structure.

Metallic Bonding and Delocalized Electrons

In metals, cohesion arises from a 'sea' of delocalized electrons that are free to move throughout the lattice. This electron gas binds the positively charged metal ions together, a concept that cannot be fully explained by simple pairwise interatomic potentials or traditional covalent bonding. Instead, metallic bonding is best described by many-body quantum mechanical models that capture the collective behavior of electrons in the metal.

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