IB SL Chemistry - Bonding

• Ionic compound: Metal + Non-metal.
• Ionic compound structure: Compact crystal lattice in ionic solids.
• Covalent compound: Sharing electrons between 2 non-metals.
• Polar Covalent: Unequal sharing due to electronegativity differences.

  • Example: H2O - Oxygen more electronegative, leading to partial charges.
• Molecular Solids: Loosely held lattice by intermolecular forces.
• Types of Forces (Covalent bonding): Hydrogen bonding, Dipole-dipole, London dispersion.
• Network Solids: Metalloids + carbon.
• Metallic compound: Metal bonding with itself.
• Metallic compound feature: Sea of delocalized electrons.
• Metallic compound properties: Source of metallic properties; forms strong bonds (cations to many electrons).
• Ionic compounds are typically soluble in water and other polar solvents.
• Ionic compounds have high melting and boiling points.
• Ionic compounds conduct electricity when dissolved in water or melted, but not when solid.
• Covalent compounds have varying solubility; depends on polarity of the compound.
• Covalent compounds generally have lower melting and boiling points compared to ionic compounds.
• Covalent compounds have weaker intermolecular forces than ionic bonds.
• Covalent compounds generally do not conduct electricity in any state.
• Metallic compounds are generally not soluble in water but may form alloys with other metals.
• Metallic compounds have high melting points and boiling points.
• Metallic compounds have excellent conductivity in solid and molten states.
• Extreme environment


  Areas that are relatively inaccessible and inhospitable to human adaptation. include hot, arid environments and high altitude cold envrionments
• Polar environment


  All year round permanent snow/ice. High latitudes above 65-70° N and parts of the Southern Hemisphere e.g. Antarctica
• Periglacial environment


  Areas on the edge of glaciers characterised by permafrost, permanently frozen ground and freeze-thaw action.
• Glacial environment


  An area covered with snow and ice on a permanent/long term basis. Have ice-sheets, ice caps and glaciers
• Cold environments


  - Found in high latitudes and altitudes

  - Located towards polar regions

  - Associated with high mountains e.g. Himalayas, Alps, Andes
• Glacier


  A large mass of slow-moving ice and snow on land
• How do glaciers form?

  Glaciers begin to form when snow remains in the same area year-round, where enough snow accumulates to transform into ice. Each year, new layers of snow bury and compress the previous layers. This compression forces the snow to form solid ice.
• Glacier accumulation


  When glaciers advance. Occurs when it is more than retreat. Includes snowfall and avalanches.

  
  

  POSITIVE REGIME
• Glacier ablation


  When glaciers retreat. Occurs when it is more than accumulation. Includes melting and sublimation of ice.

  
  

  NEGATIVE REGIME
• Glacier balance


  Net difference between total accumulation and total ablation
• Arid environments


  - Includes deserts and semi-arid areas

  - Located around the tropics and high pressure subtropical belt

  - Far from sea (continentality)

  - Rain-shadow effects
• Arid area


  Experience high daytime and summertime temperatures with a moisture deficit with mean annual precipitation below 250mm. Generally have a negative water balance.
• Semi arid area


  Areas with annual precipitation between 250-500mm and suffer from seasonal water shortages, High average temperatures.
• Evidence for climate change in glacial environments

  - 90% of glaciers are shrinking worldwide (ablation)

  - Smaller than they were in the Pleistocene
• Evidence for climate change in arid environments

  - Increased droughts has dried up headwaters of the River Volta in Sahel region

  - Forests and farmland now desert

  - Wadis present in Egyptian desert
• Plucking


  As ice moves, meltwater seeps into the joints, freezes onto the rock, then is ripped out my the moving glacier. Occurs at the base and sides of glacier.
• Abrasion


  When rock carried by the glacier scrapes and scratches the rock leaving striations
• Cirques


  a half-open steep-sided hollow at the head of a valley or on a mountainside

  
• Arete


  a knife-edge ridge formed by two cirques that have eroded back to back

  
• Pyramidal peak


  A sharp-pointed mountain peak. Form when two or more cirques meet.