year 9 chemistry recap

year 9 chemistry recap

1. what are chemicals made of?

   • Atom
     • discription of atoms have changed over time
     • structure
       • neutrons
         • has a mass of 1amu
         • are located in the centre (the nucleus) of an atom
         • neutral charge
         • together with protons they contribute to the atomic mass
         • neutrons prevent the electrons and protons from being too att
       • electrons
         • negative charge
         • orbit the atom
         • remain in orbit around atom due to attraction of positively charged protons
         • changing the number of electrons gives the atom a charge - called an "ion"
         • very low mass
       • protons
         • positive charge
         • is located in the centre (the nucleus) of the atom
         • has a mass of 1 amu (Atomic Mass Unit)
         • number of protons defines the ATOMIC NUMBER of an atom - this defines the type of element

2. chemical reactions

   • signs of a chemical change
     • gases

3. types of chemical reactions

   • acid reactions
     • acid + base produces salt + water
     • acid + metal produces salt + hydrogen
     • acid + carbonate produces salt + water + CO2
   • decomposition
   • neurtalisation