1) Chemical formulas are writen with chemical symbols. These symbols are composed of one or two letter.
Chemical symbols with one letter:
H: Hydrogen
O: Oxygen
K: Potassium
S: Sulfur
If it is just one letter, it is always a capital letter
Chemical symbols with two letters:
Br: Bromine.
Be: Beryllium
Cl: Chlorine.
Na: Sodium
If the chemical symbol has two letters, the first letter must be upperca