Ch 5 Structure and Properties of Materials

• Which metal has a higher melting point? Sodium or magnesium?

  -Magnesium

  -> higher ionic charge

  -> stronger electrostatic forces of attraction

  -> requires more thermal energy to overcome electrostatic forces of attraction
• What is an element?


  -made of only 1 element (can be atoms/molecules)

  -formed by naturally occurring

  -fixed melting point and boiling point

  -cannot be broken down into simpler substances
• What is a compound?


  -made of 2 / more elements chemically combined (chemically bonded to form ionic / covalent / metallic ) (can be molecules of atoms of the same / different elements)

  -formed from a chemical reaction

  -has a fixed ratio of its constituents

  -has different properties from constituent elements

  -fixed melting and boiling points

  -separation by thermal decomposition and electrolysis
• What is a mixture?


  -made of 2 or more elements / compounds not chemically combined

  -formed from physical mixing

  -no fixed ratio of its constituents

  -has similar properties to its constituent substances

  -melt and boil over a range of temperature

  -separation by physical methods

  *alloys require large energy changes -> not easily separated
• What group can metal elements be found?

  Group 1 - 13
• What group can non-metal elements be found?

  Group 15 - 17
• What kind of melting point / boiling point do ionic compounds have?

  -very high melting point / boiling point

  -very strong forces of electrostatic attraction between oppositely charged ions

  -large amount of thermal energy needed to overcome forces
• What kind of hardness do ionic compounds have?


  -strong electrostatic forces of attraction between oppositely charged ions

  -resistant to deforming / motion
• Why are ionic compounds brittle?


  -when enough force is applied, ions move away from their positions in the giant ionic crystal lattice structure

  -> ions of the same charge approach each other

  -repulsive forces between ions of the same charge is greater than the attractive forces between ions of the opposite charges

  -hence the giant ionic crystal lattice structure shatters
• What is the solubility of ionic compounds?


  -most are soluble in water

  -insoluble in organic solvents
• When are ionic compounds in aqueous state?


  when ionic compounds are dissolved in water
• Can ionic compounds conduct electricity?

  -ionic compounds conduct electricity in liquid / aqueous state,

  -they do not conduct electricity in solid state

  -in solid state, ions are not mobile -> only vibrate about in fixed positions

  -When the compound is in molten / aqueous state, ions are mobile and thus can conduct electricity
• What are the structural properties of giant ionic crystal lattice structures?

  large number of alternating positive and negative ions

  held together by strong electrostatic forces of attraction
• Which solid ionic compound requires the most force to break? Why?: Potassium oxide (K2O), Calcium chloride (CaCl), Calcium oxide (CaO), Potassium chloride (KCl)

  -Calcium oxide

  -highest charge -> Ca 2+ O 2 - -> 2 * 2 = 4

  -Strongest electrostatic forces of attraction