This is the order of your steps as they appear in the question:
1. Identify the elements in the compound.3. Write the chemical symbols in the order shown in the name.2. Use the periodic table to find the symbols of elements in the compound.4. Use prefixes to determine the number of each type of atom in the compound.5. Use subscripts to show the number of each type of atom in the compound.
So, arranged, the steps are:
1. Identify the elements in the compound.2. Use the periodic table to find the symbols of elements in the compound.3. Write the chemical symbols in the order shown in the name.4. Use prefixes to determine the number of each type of atom in the compound.5. Use subscripts to show the number of each type of atom in the compound.
Explanation:
The steps are better explained with an example.
Example: write the chemical formula for antimony trioxide.
Step 1: Identify the elements in the compound.
Antimony and oxygen: oxide is used for binary compounds of metals or no metals with oxygen
Step 2: Use the periodic table to find the symbols of elements in the compound.
Antimony: You can find in the column 15 and row 5. Its chemical symbol is Sb which is derived from the historical name, stibium.Oxygen: You can find it in the colum 16 and row 2. Its chemical symbol is O.
Step 3: Write the chemical symbols in the order shown in the name.
SbO
Step 4: Use prefixes to determine the number of each type of atom in the compound.
The prefix tri used for the oxygen means that there are two atoms, so there are two atoms of oxygen in the chemical formula.There is not any prefix used for antimony, so this rule is not helping to determine the number of antimonium atoms in the compound.
There are many exemptions to any rule in chemistry. So, the rules are more guidelines that must be followed with caution, which in this case means with the use of some technical knowledge.
Step 5: Use subscripts to show the number of each type of atom in the compound.
With the previous information you can write:
SbₓO₃ and you need to determine the number that must be used, instead of x, as a subscript for antimony.
You do that using the oxidation state rules:
Oxidation state of oxygen in binary compounds (except in peroxides): - 2Total charge of 3 atoms of oxygen: 3 × ( -2) = - 6.Total charge provided by antimony atoms: + 6, because the compound is neutral, when the total charge of antimony and the total charge of oxygen are added you have to get 0 charge: + 6 + (-6) = 0)The most common oxidation states to antimony are +3 and +5. Only with +3 you can form a total charge of +6 and that is multiplying by 2: 2 × (+3) 3 = +6. So the number of atoms of antimony is 2.
Finally, you get the chemical formula for antimony trioxide, using subscript 2 for antimony and subscript 3 for oxygen:
Sb₂O₃
