Atomic Structure and the Periodic Table

Atomic Structure and the Periodic Table

1. Atoms

   • All substances are made from atoms
     • They're really small
   • Nucleus
     • In the middle of an atom
     • Contains proton and neutrons
     • Positive charge because of protons
     • Whole mass of atoms concentrated in nucleus
   • Electrons
     • Move around the nucleus in electron shells
     • Negatively charged.
     • No mass
   • Neutral - have no charge overall
     • Same number of electrons and protons
     • Charge of proton and electron cancel each other out

2. Elements

   • A substance made up of atoms that all have the same number of protons in their nucleus
   • Atoms can have different number of protons, neutrons and electrons. Its the number of protons which decides the kind of atom it is.
   • Atoms of each element can be written by a letter or two
   • Isotopes
     • Have different number neutrons
     • Different forms of the same element
     • Same atomic number, different mass number

3. Compounds

   • Elements react together and the atoms form a compound
   • Substances formed from two or more elements
     • Atoms are in fixed proportions throughout the compound - held together by chemical bonds
   • Making bonds involves atoms giving away, taking or sharing electrons
   • Compound consisting of metal and non-metal
     • Metal atom loses electrons to form positive ions
     • Non-metal atoms gain electrons to form positive ions
     • Opposite charges of ions means they are strongly attracted to each other - ionic bonding
   • A compound made from non-metals consists of molecules
     • Each atoms shares an electron with another atom - this is covalent bonding