ATOMS

ATOMS

1. Atoms are made up from protons and nucleus and electrons

   • protons are positive
   • electrons are negative
     • the nucleus of the atom is made up from protons and neutrons
       • the atom number is the number of protons in the atom
         • the mass number is the total of number of protons and neutrons

2. An ion is a charged atom or a group of atoms

   • it has a positive or negative charge
     • A molecule has one or more atoms in its formula with no charge
       • if an atom loses an electron, a positive ion is formed

3. sodium chloride has a high melting point and it dissolves in water and it does not conduct electricity when solid

   • magnesium has a very high melting point and does not conduct electricity when solid

4. ionic bonding leads to large crystals and covalent bonding leads to molecules which have low melting point