Types and Properties of Solids

• Crystal or crystalline solid

  • A solid material whose components, such as atoms, molecules or ions, are arranged in a highly ordered microscopic structure.
• Ion

  • An atom or group of atoms that has a net positive or negative charge.
• Ionic crystal

  • A solid that consists of positively and negatively charged ions held together by electrostatic
• Electrostatic bonding

  • The attraction between oppositely charged ions in a chemical compound.
• Ionic bond

  • The electrostatic force that holds ions together in an ionic compound.
• Covalent bond

  • A bond in which one or more pairs of electrons are shared by two atoms.
• Crystalline solids are arranged in fixed geometric patterns or lattices. Examples of crystalline solids; ice and sodium chloride (NaCl), copper sulfate (CuSO4), diamond, graphite, and sugar (C12H22O11). The ordered arrangement of their units maximizes the space they occupy and are essentially incompressible.
• Amorphous solids have a random orientation of particles. Examples of amorphous solids are glass, plastic, coal, and rubber. They are considered super-cooled liquids where molecules are arranged in a random manner similar to the liquid state.
• The structures of crystalline solids are built from repeating units called crystal lattices. The surroundings of particles in the structure are uniform, and the attractive forces experienced by the particles are of similar types and strength.

  
• Amorphous solids soften gradually when they are heated. They tend to melt over a wide range of temperature. This behavior is a result of the variation in the arrangement of particles in their structures, causing some parts of the solid to melt ahead of other parts.

  
• X-ray Diffraction is a technique used to determine the atomic and molecular structure of a crystal, wherein atoms cause a beams of incident X-rays to diffract into many specific directions.
• Metallic Crystals: The crystal is held together by electrostatic interactions between the cations and delocalized electron. These interactions are called metallic bonds. This model of metallic bonding is called the “sea of electrons” model.

  
• Molecular crystals consist of atoms or molecules held together by hydrogen bonding, dipole-dipole interactions, and dispersion forces, which break when the crystal melts. Their valence electrons are involved in bonding and cannot move freely, making these crystals nonconductive and poor heat conductors. Additionally, they are brittle because their intermolecular forces are highly directional, causing the structure to break when disturbed.

  
• Covalent network crystals have atoms bonded in a rigid structure, like diamond (nonconductive) and graphite (conductive). In graphite, weak forces between layers allow them to slide, enabling writing with a pencil.

  
• Ionic crystals are composed of cations and anions held together by strong electrostatic forces, giving them high hardness and melting points. They conduct electricity when molten or dissolved, as ions can move freely, but remain nonconductive in solid form due to fixed ions. These crystals are brittle and shatter under pressure because shifts in ion positions create repulsive forces between like charges.