What is the primary difference between the electrical conductivity of metals and giant covalent structures like diamond?

Metals possess a 'sea' of delocalised electrons that are free to move and carry charge throughout the lattice. In contrast, diamond is an insulator because all its valence electrons are localized in strong, fixed covalent bonds, leaving no mobile charge carriers.

How does the bonding in graphite differ from the bonding in diamond?

In diamond, each carbon forms four covalent bonds in a 3D tetrahedral network. In graphite, each carbon forms only three covalent bonds in 2D hexagonal layers, with the fourth electron being delocalised between layers held by weak London forces.

Why is the melting point of silicon(IV) oxide much higher than that of a simple molecular substance like water?

Melting silicon(IV) oxide requires breaking many strong covalent bonds within a giant macromolecular lattice. Melting water only requires overcoming weak intermolecular forces (hydrogen bonds) between discrete molecules, which takes significantly less energy.

What is a common misconception regarding the strength of bonds in graphite?

A common error is assuming all bonds in graphite are weak. In reality, the covalent bonds within the hexagonal layers are extremely strong; it is only the weak London forces between the layers that allow them to slide, making the material feel soft.

Why is it incorrect to describe silicon dioxide ($SiO_2$) as a molecular substance?

Silicon dioxide does not exist as individual $SiO_2$ molecules. It is a giant covalent lattice where every atom is part of a continuous 3D network; the formula $SiO_2$ is merely the empirical ratio of silicon to oxygen atoms in that lattice.

What mistake do students often make when explaining why metals are malleable?

Students often forget to mention the delocalised electrons. Metals are malleable because the layers of positive ions can slide over each other without breaking the structure, as the 'sea' of electrons constantly maintains the electrostatic attraction between the ions.

Define a 'Giant Covalent Lattice'.

A giant covalent lattice is a macromolecular structure where a huge number of atoms are joined together by a continuous network of strong covalent bonds, resulting in high melting points and often great hardness.

What are 'delocalised electrons' in the context of metallic bonding?

Delocalised electrons are valence electrons that are not associated with any single atom or covalent bond but are free to move throughout the entire metallic lattice, acting as a 'glue' between positive ions.

What is the bond angle in a tetrahedral giant covalent structure like diamond?

The bond angle is $109.5^\circ$. This angle arises from the repulsion between the four electron pairs around each carbon atom, which arrange themselves as far apart as possible in three-dimensional space.

Why does graphite conduct electricity while graphene also conducts, but diamond does not?

Both graphite and graphene have delocalised electrons resulting from carbon atoms forming only three bonds. Diamond uses all four valence electrons in localized covalent bonds, so it has no free electrons to conduct electricity.

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3. Periodic Table & Energy

Structure & Physical Properties

Summary

The physical properties of substances, including melting points, electrical conductivity, and mechanical strength, are determined by their underlying atomic or molecular structures and the nature of the chemical bonds holding them together. This knowledge domain focuses on how metallic lattices and giant covalent networks (macromolecules) translate microscopic bonding into macroscopic characteristics.

1. Definition & Core Concepts

Lattice Structures: Most solid substances exist as regular, repeating three-dimensional arrangements of particles known as lattices. The specific geometry and bonding within these lattices dictate the substance's physical behavior.
Structure-Property Relationship: Physical properties are not arbitrary; they are direct consequences of the strength and type of forces (e.g., covalent, metallic, or intermolecular) that must be overcome to change the state or shape of the material.
Macromolecules: Also known as giant covalent structures, these involve an extensive network of atoms linked by strong covalent bonds throughout the entire sample, rather than existing as discrete small molecules.

2. Metallic Bonding & Properties

The Metallic Lattice: Metals consist of a closely packed arrangement of positive metal ions (cations) fixed in a regular pattern. These ions are surrounded by a 'sea' of delocalised electrons that have dissociated from their parent atoms.
Electrical Conductivity: Because the delocalised electrons are free to move throughout the entire structure, metals can carry an electric charge in both solid and liquid states. This mobility is the fundamental requirement for electrical conduction.
Thermal Properties: The strong electrostatic attraction between the positive ions and the delocalised electrons requires a vast amount of energy to break. Consequently, metals typically exhibit high melting and boiling points.
Solubility: Metals generally do not dissolve in water or other solvents. While polar solvents may interact with the charges in the lattice, this often leads to chemical reactions rather than simple physical dissolution.

Diagram showing a metallic lattice with positive ions and mobile delocalised electrons.

3. Giant Covalent Networks

4. Layered Covalent Structures

5. Key Distinctions

6. Exam Strategy & Tips