Molecular and Macromolecular Structures

Molecular and Macromolecular Structures

• Molecular structures: individual molecules separate from each other with weak forces between them (e.g. water, carbon dioxide)
  • Have low melting points due to weak intermolecular forces that need a small amount of energy to be broken
• Macromolecular structures: giant three-dimensional structures with many atoms strongly bonded together (e.g. ionic crystals, metals, diamond, graphite)
  • Have high melting points due to strong electrostatic attraction forces between oppositely charged ions or strong covalent bonds

Intermolecular Forces

• Weak attraction forces between molecules (intermolecular forces) in simple molecular structures
  • Need a small amount of energy to be broken, resulting in low melting points
• Strong electrostatic attraction forces between oppositely charged ions in ionic crystals
  • Need a lot of energy to be broken, resulting in high melting points

Ionic Compounds

• Have a giant structure with a regular arrangement of alternating positive and negative ions
• Have high melting points due to strong electrostatic attraction forces between oppositely charged ions
• Examples: sodium chloride (NaCl)

Metals

• Have a giant structure with rows of closely packed positive ions surrounded by a sea of delocalized electrons
• Have high melting points due to strong electrostatic attraction forces between positive ions and delocalized electrons
• Conduct electricity due to the presence of free moving electrons
• Examples: copper, zinc, sodium
• Physical properties:
  • Conduct electricity both as a solid and when molten
  • Malleable and ductile due to the layers of positive ions that can slide over each other

Diamond and Graphite

• Both are forms of carbon
• Diamond:
  • Has a giant three-dimensional structure with strong covalent bonds between carbon atoms
  • Is hard due to the rigid tetrahedral structure
  • Does not conduct electricity due to the absence of free electrons
  • Used in cutting and drilling equipment
• Graphite:
  • Has a giant three-dimensional structure with strong covalent bonds between carbon atoms
  • Is soft due to the weak attraction forces between the layers
  • Conducts electricity due to the free moving electrons
  • Used as a lubricant and electrode

Silicon Dioxide

• Has a giant three-dimensional tetrahedral structure with strong covalent bonds between silicon and oxygen atoms
• Has a high melting point due to the strong covalent bonds
• Is used in sand and has a higher melting point than carbon dioxide due to its giant structure

Other Forms of Carbon

• Fullerenes (C60):

  • Has a simple molecular structure with weak attraction forces between molecules
  • Has a lower melting point than graphite
  • Is used to deliver medicines to certain parts of the body due to its non-reactive and non-toxic properties

• Diamond and graphite:

  • Both have giant structures with strong covalent bonds
  • Diamond has a rigid tetrahedral structure, while graphite has a layer structure with weak attraction forces between the layers### Molecular Structure and Properties

• Compounds with low melting points have simple molecular structures with weak intermolecular forces that require a small amount of energy to be broken.

• Compounds with high melting points have giant covalent structures with strong covalent bonds that require a lot of energy to be broken.

Silicon Compounds

• Silicon Tetrafluoride and Silicon Tetrachloride have simple molecular structures with covalent bonds.
• Silicon Dioxide has a giant covalent structure with strong covalent bonds.

Boiling Points

• Silicon Tetrachloride has a higher boiling point than Silicon Tetrafluoride due to stronger intermolecular forces between molecules.
• Silicon Dioxide has a very high boiling point due to the strong covalent bonds in its giant structure, requiring more energy to be broken.
• The difference in boiling points between Silicon Tetrachloride and Silicon Tetrafluoride is due to the strength of intermolecular forces between molecules.

Molecular and Macromolecular Structures

• Molecular structures have individual molecules separate from each other with weak forces between them, such as water and carbon dioxide.
• Macromolecular structures have giant three-dimensional structures with many atoms strongly bonded together, such as ionic crystals, metals, diamond, and graphite.

Intermolecular Forces

• Weak attraction forces between molecules in simple molecular structures require a small amount of energy to be broken, resulting in low melting points.
• Strong electrostatic attraction forces between oppositely charged ions in ionic crystals require a lot of energy to be broken, resulting in high melting points.

Ionic Compounds

• Ionic compounds have a giant structure with a regular arrangement of alternating positive and negative ions.
• They have high melting points due to strong electrostatic attraction forces between oppositely charged ions.
• Examples include sodium chloride (NaCl).

Metals

• Metals have a giant structure with rows of closely packed positive ions surrounded by a sea of delocalized electrons.
• They have high melting points due to strong electrostatic attraction forces between positive ions and delocalized electrons.
• Metals conduct electricity due to the presence of free moving electrons.
• Examples include copper, zinc, and sodium.
• Physical properties of metals include being malleable and ductile due to the layers of positive ions that can slide over each other.

Diamond and Graphite

• Both diamond and graphite are forms of carbon.
• Diamond has a giant three-dimensional structure with strong covalent bonds between carbon atoms, making it hard and non-conductive.
• Graphite has a giant three-dimensional structure with strong covalent bonds between carbon atoms, making it soft and conductive.

Silicon Dioxide

• Silicon dioxide has a giant three-dimensional tetrahedral structure with strong covalent bonds between silicon and oxygen atoms.
• It has a high melting point due to the strong covalent bonds.
• Silicon dioxide is used in sand and has a higher melting point than carbon dioxide due to its giant structure.

Other Forms of Carbon

• Fullerenes (C60) have a simple molecular structure with weak attraction forces between molecules, resulting in a lower melting point than graphite.
• Fullerenes are used to deliver medicines to certain parts of the body due to their non-reactive and non-toxic properties.

Molecular Structure and Properties

• Compounds with low melting points have simple molecular structures with weak intermolecular forces.
• Compounds with high melting points have giant covalent structures with strong covalent bonds.

Silicon Compounds

• Silicon Tetrafluoride and Silicon Tetrachloride have simple molecular structures with covalent bonds.
• Silicon Dioxide has a giant covalent structure with strong covalent bonds.

Boiling Points

• Silicon Tetrachloride has a higher boiling point than Silicon Tetrafluoride due to stronger intermolecular forces between molecules.
• Silicon Dioxide has a very high boiling point due to the strong covalent bonds in its giant structure.
• The difference in boiling points between Silicon Tetrachloride and Silicon Tetrafluoride is due to the difference in intermolecular forces between the two compounds.

Compare and contrast molecular and macromolecular structures, including their properties and examples. Learn about intermolecular forces, melting points, and more!