Formulae and equations - OCR 21st CenturyFormulae of simple molecular compounds
Chemists use symbols and formulae to represent elements, ions and compounds. Word equations and balanced chemical equations model the changes that happen in chemical reactions.
A substance formed by the chemical combination of two or more elementA substance made of one type of atom only. is called a compoundA substance formed by the chemical union of two or more elements.. Some compounds made of non-metalElement that is a poor conductor of electricity and heat, and which forms acidic oxides. elements exist as simple moleculeA collection of two or more atoms held together by chemical bonds..
The chemical formulaA combination of symbols that indicates the chemical composition of a substance. for a simple molecule shows:
the symbols for each element in the compound
the number of atomThe smallest part of an element that can exist. of each element in each molecule
Example
A water molecule contains 2 hydrogen atoms and 1 oxygen atom. What is its formula?
the symbol for hydrogen is H
the symbol for oxygen in O
there are 2 hydrogen atoms, so a subscript 2 is added after the H (1 is not written)
H2O
Question
What is the formula for sulfur trioxide? Each molecule is made of 1 sulfur atom and 3 oxygen atoms.