Year 9 Chemistry Recap

Year 9 Chemistry Recap

1. What are Chemicals made of?

   • Atoms
     • Structure
       • Protons
         • Positively charged
         • p+
         • Are located inside the nucleus
         • Have a mass of 1
         • The number of protons defines the ATOMIC NUMBER of an atom
         • Number of protons defines the type of element
         • It is difficult to remove protons from atoms - if it changes the number of protons, it becomes a different type of element
       • Neutrons
         • Have a mass of approx 1 AMU
         • Neutral charge
         • n
         • Prevent the e- and p+ from being too attracted and condensing the atom
         • Contribute to the atomic mass
       • Electrons
         • Negatively Charged
         • Orbit the atom
         • Don't float away becasue they are attracted to the positively charged protons
         • If we changed the number of electrons in an atom, the atom becaomes charged
           • We call this an ion
           • You can change the number of electrons by giving or taking some from other atoms
         • Need to be 2 or 8 electrons on outside shell
         • e-
         • Very low mass
     • Descriptions of atoms have changed over time
     • We measure atomic mass relative to the weight of 1 atomic mass unit (amu)

2. Chemical Reactions

   • Signs of chemical reaction
     • Heat
     • Colour change
     • Gas produced
   • Acid Reactions
     • Acid + base = salt + water
     • Acid + carbonate = salt + water + carbon dioxide
     • Acid + Metal = Salt + hydrogen gas
   • Decomposition Reactions - Breaking down compounds