Chemistry

• Ionic compounds have high melting points


  It takes a lot of energy to overcome the strong electrostatic forces of attraction between oppositely charged ions
• Phosphide ion


  Formula P3-
• Phosphide has 5 electrons in its outer shell
• Sodium nitride


  Formula Na3N
• Sodium nitride contains Na+ and N3- ions
• Covalent bonding


  Shared electrons are attracted to both atoms, atoms are held together by electrostatic attraction
• Covalent bond


  • Shared electrons are attracted to both atoms, atoms are held together by electrostatic attraction
• CF4 is a molecular compound


  It has a low melting point due to relatively low electrostatic attraction and having no lone pairs of electrons
• Boron nitride structure


  Hexagonal, like diamond
• Boron nitride


  • Contains only strong covalent bonds and has a close-packed structure, therefore a large amount of heat is required to break the bonds
• Ionic bonds have a high melting point like Boron nitride
• Relative molecular mass (Mr)


  Calculated by adding the atomic masses of the elements in a compound
• Empirical formula


  The simplest whole number ratio of atoms of each element in a compound
• Mole


  The amount of a substance that contains as many particles (atoms, molecules or ions) as there are atoms in 12 grams of carbon-12
• Particles must collide in order to react
• Factors affecting reaction rate

  • Temperature
  • Surface area
  • Catalyst
  • Concentration
• Increase in temperature


  Particles gain more energy and move around faster, increasing the frequency of collisions and the rate of reaction
• Increase in concentration


  More reactant molecules in the same volume, increasing the frequency of collisions and the rate of reaction
• Increase in pressure


  Same effect as increase in concentration
• Increase in surface area

  More exposed particles available to collide, increasing the frequency of collisions
• Addition of a catalyst


  More particles have the required activation energy for a successful collision
• Disappearing cross experiment


  Use dilute hydrochloric acid, swirl to mix, start timer, stop when cross can no longer be seen
• States of matter


  • Gas
  • Liquid
  • Solid
• Gas


  • Particles have high energy, are widely spaced and randomly arranged, move rapidly and randomly
• Diffusion


  The natural movement of particles from an area of high concentration to an area of low concentration
• Definitions of a compound

  • A substance containing only one type of molecule
  • A substance containing only one type of atom
  • A substance that cannot be broken down into simpler substances
  • A substance where all the particles are the same
• Separation techniques


  • Filtration
  • Chromatography
  • Fractional distillation
• Chromatography


  Draw pencil line, add spots, place in solvent, allow solvent to move, measure distances
• Rf value


  Distance travelled by substance / distance travelled by solvent
• Subatomic particles


  • Proton
  • Neutron
  • Electron
• Isotopes


  Different types of the same element with the same number of protons but different numbers of neutrons
• Carbon has mass numbers of 12, 13 or 14
• Electron configuration


  The arrangement of electrons in an atom's shells
• The electron configuration of an atom with 19 electrons is 2,8,8,1
• Periodic table


  Columns are called groups, rows are called periods, atoms are in order of increasing atomic number
• Neon and argon


  Have full outer shells and are unreactive
• An element with electron arrangement 2,8,7 is in group 7
• Atoms have no overall charge because they contain an equal number of protons and electrons
• Mass number


  The sum of the number of protons and neutrons in an atom
• Relative atomic mass


  The average relative mass of an element's naturally occurring isotopes