Structures and properties

• What is a giant ionic structure also known as?

  A giant ionic lattice
• What results from the regular arrangement of ions in a giant ionic structure?

  The formation of a crystal
• What type of ions are present in sodium chloride?

  Positively charged Na+ ions and negatively charged Cl– ions
• What is the structure of sodium chloride crystals described as?

  A giant three-dimensional lattice structure
• Why do ionic compounds have high melting and boiling points?

  Because of the strong electrostatic forces between the ions
• Do solid ionic compounds conduct electricity?

  No, they do not conduct electricity
• What happens to ionic compounds when they melt?

  The charged ions are free to move
• What occurs when an ionic compound dissolves in water?

  The ions separate and are free to move
• What holds the oppositely charged ions together in a giant ionic lattice?

  Strong ionic bonds
• How do you draw a crystal lattice diagram?

  Start with one type of ion and connect it to neighboring ions of the opposite type
• Why do some ionic compounds have higher melting points than others?

  The greater the charge on the ions, the stronger the forces holding them together
• What is the melting point of sodium chloride?

  801°C
• What is the melting point of magnesium oxide?

  2,852°C
• What are the properties of giant ionic structures?

  • Formed by the chemical union of two or more elements
  • High melting and boiling points due to strong ionic bonds
  • Do not conduct electricity in solid form
  • Conduct electricity when melted or dissolved in water
• What are the two main types of covalently bonded substances?

  Simple covalent molecules and giant covalent structures
• What is a covalent bond?

  A bond formed when atoms share electrons to achieve a full outer shell
• Give an example of a simple covalent molecule.

  Carbon dioxide (CO2)
• Why do simple molecular substances have low melting and boiling points?

  Because little energy is needed to break the weak intermolecular forces
• What is the reason simple molecular substances do not conduct electricity?

  They do not have any free electrons or an overall electric charge
• What happens to the intermolecular forces when a simple molecular substance melts or boils?

  The weak intermolecular forces break, not the strong covalent bonds
• At room temperature, what states can simple molecular substances be found in?

  Gases, liquids, or solids with low melting and boiling points
• Why are simple molecular substances considered soft?

  Due to the weak intermolecular forces that can be broken easily
• What are the properties of simple molecular substances?

  • Low melting and boiling points
  • Do not conduct electricity
  • Soft texture
  • Exist as gases, liquids, or low melting point solids at room temperature
• How do the intermolecular forces in water compare to the covalent bonds within water molecules?

  The intermolecular forces are weak compared to the strong covalent bonds within the molecules
• What is the structure of an atom composed of?

  A nucleus containing protons and neutrons, surrounded by electrons
• What is the role of electrons in an atom?

  Electrons surround the nucleus and are involved in bonding
• What type of forces are present between simple molecules?

  Weak intermolecular forces
• What happens to the intermolecular forces during the boiling of water?

  The weak intermolecular forces between water molecules are broken
• Name two examples of simple molecular substances.

  Hydrogen and ammonia
• What is the significance of weak intermolecular forces in determining the properties of simple molecular substances?

  They lead to low melting and boiling points and softness
• How does the structure of simple covalent molecules affect their physical properties?

  The small size and weak intermolecular forces result in low melting and boiling points
• What are giant covalent structures made of?

  Very many atoms joined by covalent bonds
• How do giant covalent structures affect the properties of materials?

  They arise from bonding and affect material properties
• What is the definition of a covalent bond?

  A bond formed when atoms share electrons
• What is a lattice in the context of giant covalent structures?

  A regular grid-like arrangement of atoms
• Why are giant covalent structures extremely strong?

  Due to the many covalent bonds involved
• What are the properties of giant covalent structures?

  • Very high melting points
  • Variable electrical conductivity
• What is the melting point of graphite?

  More than 3,600°C
• Why does diamond not conduct electricity?

  Because it has no delocalised electrons
• What is silicon classified as in terms of electrical conductivity?

  A semi-conductor