3. Bonding

• what are the three types of chemical bonds?


  ionic; covalent; metallic
• why do atoms form chemical bonds?


  either transfer or share electrons to achieve a full outer shell; noble gas electron configuration
• how are ions formed?


  when atoms gain or lose electrons
• how are positive ions formed?


  when an atom loses electrons
• how are negative ions formed?


  when an atom gains electrons
• what holds together positive and negative ions?


  electrostatic attraction; very strong
• ammonium


  NH₄⁺
• carbonate


  CO₃²⁻
• hydroxide


  OH⁻
• nitrate


  NO₃⁻
• sulfate


  SO₄²⁻
• when do you get an ionic compound?


  when oppositely charged ions come together and from ionic bonds
• what is the overall charge of a compound?


  zero
• what are ionic crystals?

  giant lattices of ions
• why is the structure called a 'giant' lattice?


  it's made of the same unit repeated over and over again
• when do ionic compounds conduct electricity?


  when molten or in solution as the ions are mobile and can carry charge
• why do ionic compounds have high melting points?


  giant ionic lattices are held together by strong electrostatic forces that require a lot of energy to overcome
• what is the solubility of ionic compounds like?


  most ionic compounds dissolve in water; water molecules pull ions away from the lattice and cause it to dissolve
• what is a molecule?

  two or more atoms held together by covalent bonds
• what is a covalent bond?

  a chemical bond formed when two or atoms share electrons
• what happens to the nuclei in a covalent bond?

  positive nuclei are attracted electrostatically to the shared electrons
• what is a simple covalent compound?


  compounds that are made of lots of individual molecules
• what are atoms in molecules held by? what are the molecules in simple covalent compounds held together by?


  atoms in molecules held by strong covalent bonds; molecules in compound held by weaker intermolecular forces
• describe the structure of graphite

  carbon atoms arranged in sheets of flat hexagons covalently bonded with three bonds each; delocalised electron
• what are the sheets of hexagons in graphite bonded together by?

  weak van der Waals forces
• why can sheets slide over each other in graphite?


  weak bonds between the layers are easily broken so the sheets can slide over each other; graphite is slippery
• can graphite conduct electricity?

  delocalised electrons in graphite are free to move and carry charge along the sheets
• what is the density of graphite like?


  layers are quite far apart compared to length of covalent bonds; has low density
• does graphite have a high melting point?


  due to strong covalent bonds in hexagon sheets, graphite has high melting point (3900K)
• why is graphite insoluble in any solvent?


  covalent bonds in the sheets are too difficult to break
• what shape does diamond have?


  tetrahedral shape; crystal lattice structure
• how are the carbon atoms bonded in diamond?

  each carbon atom is covalently bonded to four other carbon atoms
• what are the properties of diamond?


  due to strong covalent bonds: high melting point (sublimes); extremely hard; good thermal conductor as vibrations travel easily; insoluble
• why does diamond not conduct electricity?

  it has no delocalised electrons to move and carry charge
• what is a dative covalent bond?


  one atom provides both of the shared electrons
• when do dative bonds form?


  when one atom has a lone pair and the other doesn't have any electrons available to share
• what does the shape of molecules and molecular ions depend on?


  number of pairs of electrons in the outer shell of the central atom
• what is a lone pair?

  pair of electrons not involved in bonding
• what is a bonding pair?


  a pair of electrons shared between two atoms
• what is a charge cloud?


  bonding pairs and lone pairs of electrons exist as charge clouds; a charge cloud is an area where you have a really big chance of finding an electron pair