Solid Structures

• Ionic compounds have high melting points due to strong electrostatic forces of attraction between oppositely charged ions, while covalent compounds like iodine have low melting points due to weak intermolecular forces.
• metallic structures?

  regular arrangement of metal cations closely packed together sea surrounded by a sea of delocalised electrons free to move randomly. Metal cations held together by valence electrons and strong electrostatic forces of attraction
• why do metals have high mp and bp?

  strong electrostatic forces of attraction between positive metal ions and the sea of delocalised electrons.
• why are metals good conductors of heat and electricity?

  presence of delocalised electrons - moving and carry a charge
• why are metals malleable and ductile?

  metal cations can slide past each other forming a new shape
• why do metals make strong alloys?

  presence of other atoms disrupts the symmetry of the layers so reduces the ability for metal cations to slide past each other
• the mp of metals increases as you?

  go across a period because the charge of the metal cation increases and there's more electrons in the sea as you go up a group
• what are the forces in a ionic crystal lattice?

  strong electrostatic forces of attraction between positive and negative ions and repulsion between ions with the same charge
• why do crystalline solids have high bp and mp?

  strong electrostatic f.o.e between oppositely charged ions needs lots of energy to break
• when can ionic crystals conduct? and how?

  when molten or in aqueous solution. ions are free to move; not in fixed positions unlike as a solid
• why are ionic crystals soluble in polar solvents like water?

  the electrostatic f.o.e between the polar water molecules and ions in the lattice is greater than the electrostatic f.o.e. between the oppositely charged ions in the lattice.
• what are unit cells?

  simplest or smallest part of a crystal which when repeated generates the whole crystal
• what is a coordination number?

  number of nearest neighbours that a given particle is in contact with in a crystalline solid.
• nacl?

  6;6
• cscl?

  8;8
• metal cation is generally --- than the non-metal anion?

  smaller
• which is larger na or cs?

  cs ion is larger so more cl ions can fit around it. if na was put in the cube, cl ions couldn't be kept apart and the crystal would break apart. C.N is lower for Na bc of this
• lattice energy?

  is the amount of energy released when a lattice is formed
• the larger the molecule?

  the greater the id-id attractive forces are
• why is iodine a solid?

  strong covalent bonds inside molecules, weak intermolecular forces between molecules
• why are molecular crystals soft?

  held by weak id-id forces
• why do molecular forces have low mp and bp?

  weak idid intermolecular forces between molecules, less energy needed to break them.
• why are molecular crystals non-conductors in any state?

  id molecules are neutral, don't have free moving electrons or ions to conduct
• why are molecular crystals virtually insoluble in water?

  can't form Hydrogen bonds with water
• water freezes? describe ice?

  no. of h bonds are maximised due to size and shape of the molecules. water adopts an open and expanded structure as the molecules are physically further apart so density of ice is less than that of water.
• how many bonds per water molecule?

  4 tetrahedral arrangement
• properties of graphite?

  conducts electricity, opaque, soft easily separated into layers bc of weak forces between layers (van Der Waals) v high sublimation point
• bond angle of graphite?

  120
• uses of graphite?

  electrodes, pencil lead/tip, lubricants
• in graphite each carbon atom is covalently bonded to three others leaving one electron delocalised and free to move
• graphite has weak van Der waals forces between layers
• diamond is an insulator, transparent, hard and has a high mp
• diamond is for drill tips and cutting tools
• diamond has each carbon covalently bonded to 4 others and has no spare electrons. It's a neutral molecule.