Concept Presentation Summary Group E: Hydrocarbons: Isomers
Grade 11 SCH3U
Avital Stopnicki and Laura McLennan
Introduction
A molecular formula for a chemical compound tells us the type and number of atoms in that compound
but not much else. Given the molecular formula C6H14, we know that the compound has 6 carbon
atoms and 14 hydrogen atoms, but we do not know how the atoms are arranged or the resulting
physical and chemical properties of the compound. We do not even know the IUPAC name of the
molecule. The unique structure of each compound dictates how the chemical compound behaves. This
subunit focuses on naming, drawing and identifying isomers – chemical compounds with identical
molecular formulas but different structures.
Expectations Addressed
B2. Investigate physical and chemical properties of elements and compounds, and use various methods
to visually represent them
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*B2.3 build molecular models for a variety of simple organic compounds [PR, AI, C]
*B3.5 explain the concept of isomerism in organic compounds, and how variations in
the properties of isomers relate to their structural and molecular formulae
B2.7 write chemical formulae… and name the compounds using the International
Union of Pure and Applied Chemistry (IUPAC) nomenclature system.
* These expectations come from SCH4U curriculum documents. The new
curriculum documents do not include hydrocarbons or isomers as part of the
expectations, however, it is indeed introduced in the grade 11 curriculum and is
included in both McGraw and the newer Nelson texts.
By the end of this sub-unit, students will be able to:
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Name hydrocarbons using IUPAC conventions
Draw structural diagrams of hydrocarbons given the IUPAC name
Identify all possible isomers given a chemical formula of a compound
Describe the general properties of alkanes, alkenes, alkynes and non-aromatic cyclic
hydrocarbons
Differentiate between structural isomers and geometric isomers of alkenes and alkynes
Prior Knowledge Required
Organic compounds are those compounds that contain carbon, with the exception of carbon monoxide,
carbon dioxide and ionic compounds containing carbon. Hydrocarbons are a subgroup of organic
compound which contain only carbon and hydrogen atoms. Students should be familiar with bonding by
carbon and hydrogen atoms and drawing Lewis structures. Students should be familiar with alkanes,
alkenes, alkynes and basic names for the C1 to C9 hydrocarbons.
Why is this topic important?
CH4 is the chemical formula for methane (a hydrocarbon) and since a hydrogen atom can only form one
single bond, there is only one possible structure for CH4. A molecule of methane is in the shape of a
tetrahedron, with the carbon atom at the centre and each of the four hydrogen atoms at a vertex.
However, as more carbons and hydrogens are added, the number of possible structures for a given
chemical formula increases. C4H10 has two possible structural arrangements, and C6H14 has five possible
structural arrangements. Compounds that have the same chemical formula but different arrangement
of atoms in space are called isomers. Although two isomers will have the same chemical formula, the
two compounds will have different chemical and physical properties.
Isomers may be either structural isomers or stereoisomers (also called geometric isomers).
Structural isomers: atoms are connected in a different order.
Stereo isomers (Geometric Isomers): atoms are connected in the same order, but oriented differently in
space.
Lesson Sequence
Day 1: Introduction to the importance of isomers (slides 2, 3 and 4)
Activity: Brainstorm Big Ideas using flowchart on board. Would be great to use smartboard if
possible for movement of molecules.
Structural Isomers
Activity: whole class / small group activity: “What does C5H12 look like?”
Discussion of possible ways to make C5H12 (or some other hydrocarbon)
– Teacher questioning (A for L) “Are these [different shapes] the same molecule? Will
they behave the same way? Do they have the same name?”
Brief lecture (SMARTboard) on structural isomers.
Optional: Activity: Card game – students each given a card with a hydrocarbon on it – must find
classmates with the same hydrocarbon and isomers of the same hydrocarbon and, as a group,
determine the total number of possible isomers for a particular molecular formula.
Students (individual, pairs, small groups) to complete questions finding all possible isomers of
various hydrocarbons. (A for L – collect workpages; A for L – conversation with students)
Day 2: Naming Structural Isomers
Steps of naming an isomer – co-construction of steps through interactive SMARTboard /
whiteboard lesson.
Activity: Card game- students to match their card containing a hydrocarbon name to its
matching structure. (A for L – observation)
Activity: naming hydrocarbons worksheets (individual, pairs, small groups) (A for L – collection
of worksheets)
Day 3: Alkenes and Alkynes – Stereo Isomers
Alkenes (double bonds) and alkynes (triple bonds).
Video: Khan academy: Stereoisomers, Enantiomers, Diastereomers, Constitutional Isomers and
Meso Compounds (http://www.youtube.com/watch?v=457xnJv80O0)
Activity: students use molecular model kits to investigate double bonds (no rotation) and cisand trans- isomers
Day 4: Lab – Reactivity of Alkenes and Alkynes
Investigation of saturated and unsaturated fats and oils (see Chemistry 11 textbook (2002,
McGraw-Hill Ryerson).
A for L and A of L – lab report
Day 5: Applications; Implications of Isomerism
Discussion of applications of isomers – drug industry; cis- and trans- fatty acids; different forms
of isopolypropene; physical characteristics of structural isomers.
Introduce post lab research assignment re: investigate the properties of saturated and
unsaturated compounds in various fats and oils, including making a comparison of geometric
isomers, the unsaturated cis and trans fatty acids, using both print and electronic resources
A of L – mini-culminating task: Students may:
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Prepare a short research paper on cis- and trans- isomers of fatty acids or isomers used
in pharmaceuticals
Write a short report on the physical and chemical differences between, and uses of two
structural isomers not already discussed in class
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Write a song or rap about isomers
Make an explanatory video on isomers
Prepare a powerpoint / SMARTboard /prezi presentation on isomers
Make a flowchart for naming isomers
Possible Student Misconceptions
Mistaking a differently drawn compound for a
structural isomer
Incorrectly identifying parent chain
Failing to notice existence of cis and transgeometric isomers
``Students’ limited concept of isomerism is due to a
discrepancy between the definition of isomerism and
its application``
Strategy
Use of molecular model kits and online
visualization tools; comparing IUPAC names of
compounds.
Teaching modeling; practice
Use of molecular model kits; drawing out
molecules in full.
Use examples of common compounds to show
application of isomers. For example slides 2, 3 and 4
of the powerpoint presentation.
Teaching Notes
Isomers – both structural and geometric - can be difficult for many students to visualize. The use of
molecular model kits and online applets which build and name molecules are essential to student
success with this topic. Students will also need to practice drawing and rotating molecules on a 2-D
plane (i.e. paper and pencil).
Resources
Mustoe, F. et al. (2002). Chemistry 11. (Whitby ON: McGraw-Hill Ryerson).
This is the Chemistry grade 11 class textbook. Unit 5 covers Hydrocarbons and Energy
Jenkins F. et al. (2001). Chemistry 11. (Toronto ON: Nelson Thomson Learning).
http://antoine.frostburg.edu/cgi-bin/senese/tutorials/isomer/index.cgi
This is an online tutorial students can use to build structural isomers.
Schmidt, H.J. (1995). Student Misconceptions – Looking for a Pattern. Science Education, vol. 81, Issue 2,
pp.123-135.
This is a research article done to investigate students` misconceptions; isomerism being one of them. In
order to identify problems students have with the isomerism concept, 12 test items were assigned to a
random sample drawn from 7441 students. The following hypothesis was made: ``Students’ limited
concept of isomerism is due to a discrepancy between the definition of isomerism and its application``.
Khan Academy: Stereoisomers, Enantiomers, Diastereomers, Constitutional Isomers and Meso
Compounds http://www.youtube.com/watch?v=457xnJv80O0
Excellent video from Khan Academy – it’s long (13+ minutes) – pick and choose the parts to share with
students.
Cerasoli, Franklin et al. (2002) American Society of Consultant Pharmacists (ASCP) : Isomer Technology
and Isolated Isomers. http://www.cmecorner.com/macmcm/ascp/ascp2002_01.htm
This site from ASCP discusses isomers at length from a 2002 symposium of medical researchers and
doctors.