Properties of simple molecules

• How do intermolecular forces affect physical properties of molecules?

  They explain differences in boiling points and density
• What are the boiling and melting points of group 4 elements?

  • Very high for giant covalent structures (e.g., carbon, silicon)
  • Quite high for metallic structures (e.g., tin)
• What are the boiling and melting points of group 5 elements?

  • Low for simple molecules (e.g., nitrogen, phosphorus)
  • High for giant structures (e.g., arsenic, antimony)
• What are the boiling and melting points of group 6 elements?

  • Low for simple molecules (e.g., oxygen, sulfur)
• How do the boiling and melting points change in groups 7 and 8?

  • Low for simple molecules or atoms
  • Increase down the groups due to stronger London forces
• Why do boiling and melting points increase down groups 7 and 8?

  More electron shells result in stronger London forces
• What happens to the size of molecules or atoms as you go down groups 7 and 8?

  They become larger with more electron shells
• What is the predicted boiling point of water based on London forces?

  About -100°C
• Why is ice less dense than liquid water?

  Hydrogen bonds in ice keep molecules apart
• What happens to hydrogen bonds as ice forms?

  Some hydrogen bonds break, allowing closer packing
• What is the current model of the atom?

  • Protons and neutrons in the nucleus
  • Electrons in electron shells
  • Nucleus is positively charged and small
• What are the relative masses and charges of atomic particles?

  • Proton: mass 1, charge +1
  • Neutron: mass 1, charge 0
  • Electron: mass negligible, charge -1
• What are isotopes?

  Atoms of the same element with different neutrons
• What happens to unstable isotopes?

  They decay through radioactive decay
• What is the actual boiling point of water?

  100°C
• Why does hydrogen fluoride have a higher boiling point than other group 7 hydrides?

  Due to hydrogen bonding between molecules