Chemical representations: formulae, models and diagrams
≈ 48 minChemical representations: formulae, models and diagrams
Chemistry uses several representations because no single diagram shows everything. A molecular formula gives atom ratios in one molecule; a structural formula gives connections; a Lewis structure shows valence electrons; a ball-and-stick model shows approximate geometry; and a balanced equation gives mole ratios between reacting substances. A coefficient belongs in front of a formula and changes the number of formula units or moles. A subscript belongs inside the formula and changes the identity of the substance. Read the question to decide which representation supplies the needed evidence.
Work it through
In 2H₂ + O₂ → 2H₂O, the subscript 2 in H₂ says every hydrogen molecule contains two hydrogen atoms. The coefficient 2 in front of H₂ says two such molecules, or two moles, are involved in the ratio. Changing H₂ to H changes the substance; changing a coefficient can balance a reaction without changing substance identity.
Mastery target
Interpret formulae, structures and balanced equations without confusing coefficients, subscripts, molecule count and atom count.
In 2H₂ + O₂ → 2H₂O, what does the coefficient 2 before H₂O represent?
Name the key chemistry term from Chemical representations: formulae, models and diagrams that best fits the explanation and visual model.
Why must you not change a subscript to balance an equation?
Which statement corrects a common misunderstanding in Chemical representations: formulae, models and diagrams?