yr 8 chemistry

• What is an atom?

  An atom is the basic unit of matter that consists of a nucleus containing protons and neutrons, surrounded by electrons. Atoms are very tiny particles that make up everything in the world (and universe).
• How many elements are there?

  118
• What is an element?

  A substance that is made out of 1 type of atom.
• What is a compound?

  A substance made up from the atoms of two or more different elements chemically bonded together.
• What is a pure substance?

  Type of matter that has the same composition throughout.
• What is an impure substance?

  An impure substance is one which contains a mixture of elements, a mixture of compounds, or a mixture of both elements and compounds.
• What is a mixture?

  Two or more elements or compounds that are mixed but not chemically bonded together. These can be separated. 
• What are the two ways we can classify elemtents?

  Metals and Non - Metals.
• When does a compound end in '-ide'?

  If a compound is made of a metal and a non-metal then the metal comes first in the name, and the ending of the non-metal becomes “-ide”.
• When does a compound end in '-ate'?

  If a compound is made of 3 elements (one of which is a metal) and one of those is oxygen then the name ends in “-ate”. The “-ate” bit tells us that oxygen is present.
• What is oxidation?

  Oxidation is a chemical reaction in which a substance loses electrons and an element or compound gains oxygen atoms.
• Is combustion an example of oxidation reaction?

  Yes
• What is reduction?

  Reduction is gain of electrons, loss of oxygen or gain of hydrogen.
• What does the Law of Conservation Of Mass state?

  It states how the total mass of the products formed in a reaction is equal to the total mass of the reactants. The mass is conserved in a chemical reaction.
• What is an exothermic reaction?

  An exothermic reaction is a chemical reaction that releases heat to its surroundings.
• What is an endothermic reaction?

  An endothermic reaction is a chemical reaction that takes in energy from the surroundings.
• Particles


  Small balls that make up everything in the universe
• You cannot see the particles with your eyes, but scientists have lots of ways to detect them
• The particles that make up everything in the universe can be arranged in lots of different ways
• How the particles are arranged

  Determines whether something is a solid, liquid or gas
• Gas


  • Particles move randomly in all directions and travel very fast
  • Particles do not touch and are very spread out
  • Particles sometimes bounce off each other (and off the walls of any container) if they happen to collide
• Liquid


  • Particles can move freely over each other
  • Particles are arranged randomly
  • Not all of the particles touch, but each particle will be touching at least one other particle
  • There are small gaps between particles
• Solid


  • Particles are arranged in a regular pattern of lines and rows
  • Particles cannot move away from the position they are locked in, they just vibrate on the spot
  • Particles are very close together and they always touch
• Melting


  1. Solid particles get some extra energy, which makes them vibrate faster and faster until they have enough energy to break away from their fixed position

  2. Particles can then move freely over each other, and have turned into liquid particles

  3. Heating something will give solid particles enough energy for them to adopt a liquid particle arrangement
• Condensation


  1. Cooling down a gas reduces the energy of the particles

  2. Particles slow down and clump together, taking the arrangement of a liquid
• Boiling


  1. Heating liquid particles makes them move faster and faster

  2. Eventually, the liquid particles will be moving very quickly and in random directions, without being connected to any other particles – they have changed into the gas particle arrangement
• Water boils at 100oC
• Evaporation


  1. Different particles in a liquid have different amounts of energy

  2. Some particles will gain enough energy to break free and will become a gas

  3. A liquid boils when every particle has this much energy
• Freezing


  1. Cooling a liquid down makes the particles travel slower and slower until they are just vibrating in a fixed position and are all very close together

  2. The particles will then look like the particle arrangement in a solid and the substance has frozen
• When water freezes to ice, it happens at 0oC