Formulae, Functional Groups and TerminologyCambridge IGCSE Chemistry: Flashcards
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Define molecular formula.
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- Define molecular formula.
- The molecular formula shows the number and type of different atoms present in one molecule of a compound.
- What is the empirical formula?
- The empirical formula is the simplest whole number ratio of different atoms or ions present in a compound.
- How do you deduce a molecular formula from a model or diagram showing atoms?
- Count the total number of each type of atom present in the molecule. This count gives the molecular formula.
- What are state symbols and what do they represent?
- State symbols show the physical state of substances in equations: (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous solution.
- Define a word equation.
- A word equation uses the names of reactants and products written out in words, separated by an arrow showing the direction of reaction.
- What is a symbol equation?
- A symbol equation uses chemical formulae to represent the reactants and products, showing what atoms and molecules are involved in a reaction.
- How do you construct a balanced symbol equation with state symbols?
- Write the chemical formulae for reactants and products, balance the equation so equal numbers of each atom appear on both sides, then add state symbols (s), (l), (g), or (aq) to each substance.
- How do you deduce an ionic formula from the charges on ions?
- Use the charges to determine how many of each ion are needed to balance overall charge. The positive and negative charges must be equal in the formula.
- What information must you use to deduce a formula from relative numbers of ions?
- Count the number of positive ions and negative ions present. The ratio of these numbers gives the ionic formula.
- Define a functional group.
- A functional group is a group of atoms within a molecule that determines the characteristic chemical reactions of that molecule.
- What is an ionic equation?
- An ionic equation shows only the ions and molecules that actually participate in the chemical reaction, omitting spectator ions that do not change.
- How do you construct an ionic equation from a full symbol equation?
- Write the full balanced symbol equation, identify the spectator ions (ions that appear unchanged on both sides), then remove the spectator ions to show only the reacting species.
- Explain the relationship between empirical and molecular formulae.
- The molecular formula is always a simple whole number multiple of the empirical formula. For example, if the empirical formula is CH₂, the molecular formula could be C₂H₄, C₃H₆, etc.
- How do you determine the empirical formula from relative numbers of atoms in a diagram?
- Count the number of each type of atom, then reduce to the simplest whole number ratio by dividing by the smallest number.
- What must be included when writing a symbol equation for a chemical reaction?
- The chemical formulae of all reactants and products must be correct, the equation must be balanced so equal numbers of each atom appear on both sides, and state symbols should be included.