Formulae of Ions

ION: An atom or group of atoms in which the total number of elctrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. When an atom loses or gains an electron it becomes an ion.

 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++

CATION: A positively charged ion. Most cations are metal ions, e.g. Na+. 

--------------------------------------------------------

ANION: A negatively charged ion. Anions usually contain a full outer orbital of electrons. Non-metals form anions but complex ions can also be anions.

      1+                    2+                         3+

H⁺         Hydrogen               Mg²+      Magnesium           Al³⁺        Aluminium    

Li⁺        Lithium                   Fe²+       Iron (ll)                   Fe³+      Iron (lll)    

Na⁺       Sodium                  Ba²+       Barium     

K⁺         Potassium             Cu²+       Copper (ll)    

Cu⁺       Copper (l)             Ca²⁺        Calcium   

Ag⁺       Silver                     Pb²⁺        Lead

NH₄⁺    Ammonium              Zn²⁺        Zinc

            1-                               2-    

OH^-           Hydroxide                                O^2-            Oxide           

HCO₃^-       Hydrogencarbonate                CO₃^2-        Carbonate              

Cl^-             Chlorine                                 SO₄^2-         Sulphate

Br^‑            Bromine                                  S^2-             Sulphide 

I^-               Iodide           

NO₃^-         Nitrate      

                          [Notable:  HNO₃^-    Nitric Acid]             

Working out the formula for common compounds is easy, It's all about balancing!

If we take a compound such as Iron(ll) nitrate;

• We know Iron (ll) ion has a charge of 2+ and nitrate ion has a charge of 1-.
• So to balance this up with have to include an additional nitrate ion to match Iron(ll)'s charge of 2. 
• This means the compound is written as Fe (NO₃)₂ the reason we include brackets is that we need 2 nitrates and if we wrote the compound without brackets it would look like 32 and people might get mixed up.(NB: The numbers should be written in subscript)

 Lets do another, Aluminium hydrogencarbonate;

• Aluminium has a charge of 3 + and hydrogencarbonate has a charge of 1-.
• So we need 3 hydrogencarbonate ions to balance this up.
• The compound is written as Al (HCO₃)₃         

Can you do these? barium hydroxide, lithium sulphate, calcium nitrate