How To Write Chemical Symbols?
Updated: May 4, 2020

Chemical symbols are used to represent an atom or elements. For example, the chemical symbol for hydrogen is H.
Symbols For Common Ions are as follows:

The valency of an element is needed to be able to write the formulae of a compound. Recall that valency of an element is the number of valence electrons the element has. In ionic compounds, the valency of an ion is equal to its charge.
*Tip: Valence electrons means outermost electrons or the electrons at the outermost shell
Writing Formula For Ionic Compounds
Ionic compounds are made up of positive and negative ions. In an ionic compound, the total positive charges must equal the total negative charges → the total charge on the ionic compound must be zero.
*Refer to Ionic Bond and Covalent Bonds notes to clearly understand how each of the ions is formed and combined to be the following compounds.
Make use of the table of symbols for common ions to write out the formula for ionic compounds
Examples:
Sodium chloride
Relevant ions are: Na+ and Cl−
Simplest ratio to obtain zero total charge: 1 : 1
Formula: NaCl
Calcium Nitrate
Relevant ions are: Ca2+ and NO3−
Simplest ratio to obtain zero total charge: 1:2 → this means 1 of calcium ion and 2 of nitrate ions to form calcium nitrate
Formula: Ca(NO3)2
Note: The brackets are used to indicate that there are two NO3 ions in the ionic compound
Sodium Sulphate
Relevant ions are: Na+ and (SO4) 2−
Simplest ratio to obtain zero total charge: 2:1
Formula: Na2SO4

Writing Formula For Covalent Compounds
The way to write the formula for covalent compounds is slightly different from that of ionic compounds. You will need to know the number of valence electrons that each of the elements has.
*Refer to Ionic Bond and Covalent Bonds notes to clearly understand how each of the ions is formed and combined to be the following compounds.
Examples:
Hydrogen Chloride
Relevant elements: H and Cl
Valence electrons: 1 for H and 7 for Cl
1 covalent bond is formed
Formula: HCl
Water
Relevant elements: H and O
Valence electrons: 1 for H and 6 for O
O requires 2 electrons to achieve stable noble gas configuration. H provides 1 electron
Hence, 2 H will be required for O to achieve a stable noble gas configuration
2 covalent bonds are formed
Formula: H2O
Carbon Dioxide
Relevant elements: C and O
Valence electrons: 4 for C and 6 for O
C provides 4 electrons but O only requires 2 electrons to achieve a stable noble gas configuration
Hence, 2 O will be required for C to achieve a stable noble gas configuration
2 covalent bonds are formed
Formula: CO2
