1A

1A

1. Atoms & Elements

   • Nucleus
     • Middle of Atom but tiny
     • Contains protons and neutrons
     • Protons are positiveley charged
     • Neutrons have no charge
     • Has a positive charge
   • Electrons
     • Move around nucleus
     • Negatively charged
     • Small but cover large space
     • Occupy shells around nucleus
   • Number of protons= number of electrons
   • If number of electrons change atom becomes charged and is an ion
   • Elements have one type of atom only

2. Periodic Table

   • Vertical columns= Groups
   • All elements in a group have same no. electrons in outer shell
     • This is why elements in same groups have similar properties

3. Electron Shells

   • 1st shell= 2
   • 2nd shell= 8
   • 3rd shell= 8

4. Compounds

   • When different elements react atoms form bonds which form compounds
   • Ionic Bonding
     • Opposite charges of ions mean compunds are attracted
   • Covalent Bonds
     • Each atom shares an electron with another atom