Chemistry Revision

Chemistry Revision

1. Atoms, Compounds and Isotopes.

   • Atoms are very small. They can contain THREE even smaller particles - PROTONS, NEUTRONS and ELECTRONS.
     • 1) DIFFERENT elements will have DIFFERENT numbers of PROTEIN.
       • 2) To get the number of NEUTRONS, just TAKE AWAY the ATOMIC NUMBER from the MASS NUMBER.
         • 3) Electrons aren't counted in the mass number because their RELATIVE MASS is very small.
   • The mass number is the top number and it tells you the total number of protons and neutrons.
     • The atomic number which is the bottom number, tells you the number of protons.
   • Compounds Are Chemically Combined.
     • Carbon + Oxygen = Carbon Dioxide
       • Compounds are made when atoms of TWO OR MORE elements are CHEMICALLY COMBINED.
         • For example, carbon dioxide is a compound. It's made from a CHEMICAL REACTION between carbon and oxygen.
   • Isotopes Are the Same Except From The Number Of Neutrons
     • Isotopes are: ATOMS of the SAME ELEMENT, which have the SAME number of PROTONS but a DIFFERENT number of NEUTRONS.

2. Ionic Bonding

   • Transferring Electrons
     • In IONIC BONDING, atoms LOSE OR GAIN ELECTRONS to form IONS.
       • Ions can have a POSITIVE (+) or NEGATIVE (-) CHARGE.
         • Atoms with just ONE OR TWO ELECTRONS in their outer shell (highest energy level) want to LOSE these.
           • Then they will have a FULL OUTER SHELL.
           • A Nearly Full Outer Shell Wants To Gain Electrons.
             • Atoms with NEARLY FULL outer shells want to GAIN an EXTRA ONE OR TWO ELECTRONS to fill the shell up.
               • So they TAKE an electron from an atom that wants to lose one.
           • Ionic Compounds Are a Giant Regular Structure of Ions.
             • IONIC COMPOUNDS have a GIANT IONIC LATTICE structure.
               • SODIUM CHLORIDE (salt) is a GIANT IONIC LATTICE.
             • Ionic compounds all have HIGH MELTING POINTS and HIGH BOILING POINTS.
               • It takes a lot of ENERGY to break the STRONG BONDS.
                 • When ionic compounds MELT, the ions are FREE TO MOVE. This mean they'll CARRY ELECTRIC CURRENT.
                   • Ionic compounds DISSOLVE EASILY in water. The ions SEPERATE and are FREE TO MOVE. This means they'll CARRY ELECTRIC CURRENT.