Chemistry

• States of matter


  The different physical forms that a substance can take (solid, liquid, gas)
• Changes of state


  Particles lose or gain energy and change characteristics
• Kinetic particle theory


  • All substances are made up of particles
  • The particles are attracted to each other (some strongly and some weakly)
  • The particles move around (meaning they have kinetic energy)
  • The kinetic energy of the particles increases with temperature
  • A substance can be a solid, liquid or a gas and can change state from one to the other
  • Each state has different characteristics based on the way its particles are arranged
• Increase in pressure


  Decrease in gas volume
• Increase in temperature


  Increase in pressure of the gas but also an increase in volume
• Brownian motion


  The random movement of particles as they bump into each other
• Diffusion


  The movement of particles from and area of high concentration to an area of low concentration
• Rate of diffusion


  • Depends on the mass of the particles: the lower the mass, the faster the rate of diffusion
  • Depends on the temperature: the higher the temperature, the faster the rate of diffusion
• Boiling


  When all liquid particles become gas particles at the boiling point
• Evaporation


  When the particles on the surface only become a gas and can happen at any temperature
• Elements are each made up of one type of atom which is different to the atoms of every other element
• Structure of an atom

  • Protons (positive charge)
  • Neutrons (no charge)
  • Electrons (negative charge)
• Shells


  The outer layers of the atom where the electrons are
• Electronic arrangement


  How electrons are arranged in their shells
• Isotopes


  Different atoms of the same element with the same number of protons but different numbers of neutrons
• Isotopes of the same element have the same chemical properties as they have the same electronic configuration
• Relative atomic mass (Ar)


  (% of isotope 1 x mass number of isotope 1) + (% of isotope 2 x mass number of isotope 2)/100
• Cation


  An atom that loses electrons and has a positive charge
• Anion


  An atom that gains electrons and has a negative charge
• Ionic bonding


  A strong electrostatic attraction between oppositely charged ions
• Giant lattice structure of ionic compounds

  • A regular arrangement of alternating positive and negative ions
• Covalent bond


  When a pair of electrons is shared between two atoms leading to noble gas electronic configurations
• Covalent molecules


  • Tend to have low melting and boiling points
  • Forces within the molecules are strong but the forces between the molecules (intermolecular forces) are weak
  • Do not conduct electricity, are usually soft and brittle and tend to be insoluble in water
• Ionic substances


  • Do not conduct electricity as solids, but they do conduct electricity when molten or aqueous (dissolved)
  • Tend to have high melting and boiling points
• Giant covalent structures


  Have very high melting and boiling points and are usually hard
• Allotropes


  • Diamond and carbon
  • Silicon (IV) oxide
• Metallic bonding


  The electrostatic attraction between the positive ions in a giant metallic lattice and a sea of delocalised electrons
• Metals


  • Good conductors of heat and electricity
  • Have high melting and boiling points
  • Malleable (can be bent and pressed into shape)
  • Ductile (can be drawn out into wires)
• Periodic table


  An arrangement of elements in periods and groups in order of increasing proton number
• Property


  A characteristic feature of any substance
• Reactivity in metals


  Increases down the group and from right to left
• Reactivity in nonmetals and semi-metals

  Increases up the group and from left to right (not including Group 0)
• Alkali metals


  • Soft and can be cut by a knife
  • Low density - float on water
  • Density increases down the group
  • Low melting and boiling points, which decrease down the group
  • Good conductors of heat and electricity
  • Shiny when freshly cut
• Reactivity in alkali metals

  The further you go down the group, the more reactive the alkali metals become
• Alkali metal + water


  Metal hydroxide + hydrogen
• All alkali metals react with air to form metal oxides, producing a layer of black oxide called tarnish
• Uses of alkali metals


  • Lithium: batteries, alloys, medical treatment, submarines and space vehicles
  • Sodium: street lights and nuclear reactors
  • Potassium: fertilizers, fireworks, explosives and food preservation
• Halogens


  • Very reactive nonmetals
  • Found as compounds in metals
  • Can easily obtain a full outer shell by gaining one electron
  • Form negative ions with a -1 charge
  • Found as diatomic molecules
  • Going down the group, the melting point, boiling point, size and density increase and reactivity decreases
  • Do not conduct electricity
  • Brittle and crumbly when solid
  • Poisonous and smelly
• Halogens and metals react

  Form ionic compounds called metal halides (a type of salt)
• Chlorine


  Pale yellow-green gas at r.t.p. and very pale green (usually appears colourless) in an aqueous solution