A chemical formula is basically an expression that tells the type and number of atoms present in a molecule of a substance. You may also say that a chemical formula shows the written combination of element symbols that show the number of atoms combined in a chemical compound.
It is important to have the knowledge of valance and oxidation numbers to be able to able to write chemical formulas. It's equally important to follow the capitalization rules for elemental symbols along with having information about atomic structure of those elements. Writing the second letter of a chemical formula incorrectly can dramatically change the meaning of a chemical formula.
To write a formula correctly, it's important to understand the periodic table.
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