Displayed formulae
4 marks · Normal| Molecule | Displayed formula |
|---|---|
| Ethene | C = C with each C joined to 2 H |
| Propene | C = C - C with hydrogens to fill remaining bonds |
| Butene | C = C - C - C with hydrogens to fill remaining bonds |
Use the displayed formulae in the table to answer the questions.
Identify the type of bond connecting the first two carbon atoms in all molecules.
State the total number of single and double bonds in propene.
Describe how the displayed formula helps you determine the locations of hydrogen atoms in butene.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Double bond
(b) 5 single bonds and 1 double bond
(c) The displayed formula shows which carbon atoms have free bonds remaining after forming C–C bonds, indicating where hydrogens must be added so each carbon has four bonds.
Common mistakes: Counting double bonds or single bonds incorrectly; Forgetting about all hydrogens
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correctly identifies double bond between first two carbons.
M1 (b) · 1 mark · Counts and states number of single bonds in propene.
A1 (b) · 1 mark · States there is 1 double bond in propene.
B2 (c) · 1 mark · Explains position of hydrogens is fixed by filling remaining bonds for carbon to four.
Worked solution
a) The first two carbon atoms in each molecule are joined by a double bond.
b) In propene: C1=C2–C3. C1 has 2 H, C2 has 1 H, C3 has 3 H. Bonds: C1–C2 (double), C1–H (2), C2–H (1), C2–C3 (single), C3–H (3). Total: 5 single, 1 double.
c) Any bond not connecting carbons must connect to a hydrogen to satisfy the rule that each carbon makes four bonds.