Representing organic molecules
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Question
What is an empirical formula?
Answer
The **simplest whole-number ratio** of the atoms in a compound (e.g. CH_{2}O for glucose).
Question
What is a molecular formula?
Answer
The **actual number** of each type of atom in one molecule (e.g. C_{6}H_{12}O_{6} for glucose).
Question
What is a structural (full) formula?
Answer
A diagram showing **every atom and every bond** in the molecule.
Question
What is a condensed formula?
Answer
Atoms written **grouped in a line** with the bonds implied (e.g. CH_{3}CH_{2}OH).
Question
What is a skeletal formula?
Answer
Only the **carbon skeleton** drawn as lines; carbons are corners/ends and **H on carbon is implied**; functional groups are shown.
Question
In a skeletal formula, what is at each corner and line-end?
Answer
A **carbon** atom (each with enough H to make four bonds, not drawn).
Question
How do you get an empirical formula from a molecular one?
Answer
Divide **every** subscript by their **highest common factor** (e.g. C_{6}H_{12}O_{6} ÷ 6 = CH_{2}O).
Question
What are structural isomers?
Answer
Molecules with the **same molecular formula** but a **different arrangement** of atoms (different connectivity).
Question
Three ways structural isomers can differ?
Answer
Chain **branching**, **position** of a group, or different **functional group / class**.
Question
How do you draw a valid structural isomer?
Answer
Keep the **same molecular formula** but **change the connectivity** — never just rotate or flip the original.
Question
Are CH_{2}O and C_{2}H_{4}O_{2} the same molecule?
Answer
No — CH_{2}O is an **empirical** formula; C_{2}H_{4}O_{2} (ethanoic acid) is one **molecular** formula with that ratio.
Question
Is a rotated copy of a molecule a structural isomer?
Answer
**No** — it is the same molecule; an isomer must have a genuinely different structure.
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Full study notes for Representing organic molecules
Topic 3.2 hub
Functional groups: classification of organic compounds
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