Physical Properties of Different Crystal Structures

This page discusses how the type of bonding and crystal structure affects the physical properties of substances, including boiling/melting points, solubility, and conductivity.

Ionic Crystal Structure:

• Has high melting and boiling points due to strong electrostatic forces of attraction in the ionic lattice
• Cannot conduct electricity when solid, only when molten or dissolved
• Often brittle due to repulsion between like charges when layers are distorted

Vocabulary: Lattice - a regular repeating arrangement of atoms, ions, or molecules in a crystal.

Metallic Structure:

• Good conductors of heat and electricity due to delocalized electrons
• Malleable as layers of positive ions can slide over one another
• High melting points due to strong electrostatic forces between positive ions and delocalized electrons

Highlight: Most metals are solid at room temperature, with mercury being a notable exception.

Simple Molecular Structure:

• Consists of covalently bonded molecules held together by weak van der Waals forces
• Low melting and boiling points due to weak intermolecular forces
• Poor conductivity due to lack of charged particles

Example: Water has a higher boiling point compared to other simple molecular substances due to the presence of hydrogen bonds.

Macromolecular Structures

This page focuses on macromolecular structures, which are covalently bonded into giant lattice structures.

Characteristics of Macromolecular Structures:

• Each atom has many covalent bonds, resulting in high melting points compared to other crystal structures
• The strength of the covalent lattice makes these substances rigid

Example: Diamond is an example of a macromolecular structure, made up of carbon atoms each bonded to 4 other carbon atoms, making it very hard.

Graphite:

• Another macromolecular structure made of carbon atoms
• Each carbon atom is bonded to 3 other carbon atoms in flat sheets
• Electrons not used in bonding are free to move between layers, allowing graphite to conduct electricity

Highlight: The difference in bonding structure between diamond and graphite results in vastly different properties despite both being made of carbon.

Vocabulary: Graphene - a single layer of graphite, with unique properties due to its two-dimensional structure.

The page includes diagrams illustrating the structures of diamond, graphite, and graphene, highlighting the differences in their atomic arrangements.

Ionic, Covalent, and Dative Bonding

This page introduces the three main types of chemical bonding: ionic, covalent, and dative (coordinate) bonding. It also touches on metallic bonding.

Ionic Bonding occurs between metals and non-metals. Electrons are transferred to achieve full outer shells, creating charged particles called ions. These oppositely charged ions attract each other through electrostatic forces, forming a giant ionic lattice.

Definition: Ionic bonding is the electrostatic attraction between oppositely charged ions formed by electron transfer between metals and non-metals.

Covalent Bonding takes place between two non-metals. Electrons are shared between the outer shells of atoms to achieve a full outer shell. Multiple electron pairs can be shared, resulting in multiple covalent bonds.

Dative Bonding, also known as coordinate bonding, forms when both electrons in the shared pair come from a single atom. This is indicated by an arrow from the lone pair.

Highlight: Once a dative bond has formed, it behaves like a standard covalent bond in reactions.

Metallic Bonding consists of a lattice of positively charged ions surrounded by a sea of delocalized electrons. This creates a strong electrostatic force of attraction between the oppositely charged particles.

Example: The greater the positive ion charge in metallic bonding, the stronger the attractive force due to more electrons being released into the electron sea.