year 9 chemistry recap

year 9 chemistry recap

1. what are chemicals made of

   • atoms
     • description of atoms have changed over time
     • structure
       • protons
         • positively charged
         • mass of 1 amu ( atomic mass unit )
         • located in the nucleus ( middle )
           • help keep electrons around the atom
         • number of protons defines the atomic number of an atom - this defines the type of element
         • difficult to remove protons from atoms -- if it changes the number of protons , it becomes a different type . of element
       • neutrons
         • neutrally charged
         • mass of 1 amu ( atomic mass unit )
         • contribute to the atomic mass
         • neutrons prevent the electrons and protons from being too attached and condensing the atom
       • electrons
         • negatively charged
         • orbit the atom
         • maintain in orbit round the atom due to attraction to positively charged proton
         • changing the number of electrons gives the atom a charge -- called an ion
           • ion
             • electric charge due to loss or gain in electrons
         • very low mass

2. chemical reactions

   • signs of chemical reactions
     • odour produce
     • types of chemical reactions
       • acid
         • acid + metal produce salt + hydrogen gas
       • decomposition
         • breaking down compounds
       • neutralisation