GCSE AQA Chemistry 1 Elements & Compounds

GCSE AQA Chemistry 1 Elements & Compounds

1. Atoms

   • Nucleus in the middle
     • Contains protons & neutrons
       • Protons = Positive Neutrons = Neutral
         • Positive charge overall
   • Electrons
     • Move around nucleus in shells
       • Negatively charged
   • No overall charge
     • No. of protons = no. of electrons
       • Add/remove electrons - atom becomes charged (ion)

2. Elements

   • Contain 1 type of atom
     • No. of protons decides type
   • About 100 different ones

3. The Periodic Table

   • Elements with similar properties in same group/column
     • All elements in group have same no. of electrons in outer shell
   • Top number: Mass no.
     • Total no. of protons & electrons
   • Bottom number: Atomic no.
     • No. of protons (same as no. of electrons)

4. Electron shells

   • Lowest energy shells always filled first
   • Only certain no. allowed in each shell: 2 in 1st shell, 8 in 2nd shell & 8 in 3rd shell
   • Full shells are ideal
     • Otherwise will react to fill

5. Compounds

   • Form chemical bonds with other atoms to make compounds - difficult to separate again
     • Making bonds: Giving away/taking/sharing electrons
   • Ionic Bonding
     • Metal & Non-metal -> IONS
       • Metal atoms lose electrons to form positive ions
         • Non-metal atoms gain electrons to form negative ions
           • Opposite charges strongly attracted to each other
   • Covalent bonding
     • Non metals -> MOLECULES
       • Sharing electrons
         • Makes enough to fill outer shell
   • Properties of compound different from original elements'
     • Can be lattices/molecules