MYP integrated science

C4.1 - Carbon’s Bonding Rules and Molecular Geometry

In grade 9, you learned about atomic structure and how electrons are arranged in shells. In this lesson, we focus on carbon — an element with unique bonding properties that allow it to form an enormous range of compounds. Carbon is the foundation of organic chemistry because it is tetravalent: it can form four covalent bonds.

Carbon atom

Why is carbon tetravalent?

Carbon has four valence electrons in its outer shell. To achieve stability, it shares these electrons with others, forming four covalent bonds. These bonds arrange themselves to minimise repulsion, which gives rise to predictable molecular shapes.

Methane molecule

Activity 1: Map Pin Molecular Geometry

Map Pin Challenge

The aim of the following activity is to explain why carbon bonds in a tetrahedral arrangement when bonding to four other atoms.

In groups, use large polystyrene spheres and map pins:

Place 2, 3, 4 and 5 pins as far apart as possible on the surface.
Identify the shapes adopted (linear, trigonal planar, tetrahedral, trigonal bipyramidal).
Estimate bond angles using geometry and trigonometry.

Extension: use coloured pins to represent non-bonding electron pairs (electron pairs that are not used for bonding) and compare electron-domain geometry with molecular shape.

Activity 2: Introducing Molymods

Molymod Models

Explore molecular geometry further by building methane, ammonia, and water with molymods.

Go to the Molview website on your device (www.molview.com) and examine the structures of the molecules that you are building with MolyMods. Use the Model tab to change the view from "ball and stick" to "Van der Waals spheres". Which do you think is closer to the "real" shape of a molecule.

Explore a few more molecules, such as ethane, butane, benzene and ethanol.

Compare your ball-and-stick models with space-filling representations in MolView.
Discuss: are molymods a good representation of molecules? What do they show well, and what do they miss?

Drawing Molecules

We also need a way to represent molecules on paper. Chemists use Lewis structures (dot-cross diagrams) to show bonding pairs and lone pairs of electrons. These diagrams connect the visual models with the abstract electron count.

Examples

CH₄ (Methane)

four single bonds, tetrahedral shape.

NH₃ (Ammonia)

three single bonds and one lone pair, trigonal pyramidal.

H₂O (Water)

two single bonds and two lone pairs, bent shape.

Summary

Carbon forms four covalent bonds; electron pairs arrange to minimise repulsion.
Electron-domain geometry (pairs) is not always the same as the molecular shape (atoms).
Models (pins, molymods, MolView) and Lewis structures connect counting electrons to 3D shape.

Check your understanding

Explain why carbon forms four covalent bonds (tetravalency) in terms of valence electrons.
What is the difference between electron-domain geometry and molecular shape? Give an example.
State the typical bond angle for a tetrahedral arrangement and outline (in words) why it arises.

C4.2 - Allotropes of Carbon

Many elements exist in more than one physical form called allotropes. Changes in stucture and bonding between atoms explain dramatic differences in properties such as hardness, conductivity, and stability.

Carbon allotropes are remarkable in their differences even though they all contain only carbon atoms.

Carbon allotropes

Model & Compare

Diamond – 3D network (each C is tetrahedral); very hard, electrical insulator.
Graphite – 2D layers (sp² trigonal planar) with delocalised electrons; soft, conducts along layers.
Graphene – single graphite layer; very strong, excellent conductor.
Fullerenes / nanotubes – curved cages/tubes with unusual mechanical/electronic properties.

Using the Molymods, build small lattice fragments (diamond tetrahedra; graphite hexagonal sheet). Sketch graphene, fullerene (C₆₀), and a nanotube.

Graphene

Graphene is considered a new substance even though its been around for many years. When a pencil makes a mark on a piece of paper the black line consists of layers of graphite, called graphene.

Recently researchers found that these graphene layers have remarkable properties and if large sheets of graphene could be manufactured then many technological innovations would become possible.

Graphene in batteries

Allotropy across other elements

Compare & Explain

Many elements have allotropes, the stability of which is dependent on the ambient pressure and temperature.

Oxygen: O₂ (stable) vs O₃ ozone .
Phosphorus has three common allotropes, white P (P₄ tetrahedra; strained, reactive) → red P (polymeric, more stable) → black P (layered, most stable).
Tin has two common allotropes, β-Sn (white, metallic, stable above ~13 °C) ⇄ α-Sn (grey, brittle, “tin pest”, stable below ~13 °C).

What does the term "stability" refer to in this context?

This is a fundamental concept in chemistry.

Case Study: Napoleon’s Buttons (Myth-busting)

The story claims tin buttons on uniforms crumbled in the 1812 Russian winter due to tin pest (β-Sn → α-Sn).

Evaluate the plausibility - fact check:

Did soldiers uniform buttons actually contain tin?
Were the temperatures low enough when Napoleon attacked Moscow?
What alternative explanations exist?

Summary

Allotropy shows how the same element can display radically different behaviours when its atoms connect in different ways.

Understanding structure helps to explain properties and stability trends across elements.

Check your understanding

Why does graphite conduct electricity while diamond does not?
Why is the formation of ozone in the upper atmosphere essential to life on our planet?
Why does tin undergo the α ⇄ β transition around 13 °C, and what consequence does this have in cold climates?

C4.3 Organic Nomenclature Basics (Part 1)

In this lesson you will learn the core language of organic chemistry: how to name simple molecules using roots and functional group suffixes. We focus on straight-chain compounds (C1–C6) before moving to branching and locants.

Roots and homologous series

Build the backbone

Using molymods, build methane → hexane (C1–C6). Say the names out loud as you build.
Record the general formula for the alkane homologous series.
Discuss: how does adding one CH₂ unit change properties (mass, b.p.)?

Functional group suffixes

Spot the group

Add a double bond to make an alkene (–ene). Add a triple bond for an alkyne (–yne).
Swap an H for –OH to make an alcohol (–ol). Swap an H for –Cl / –Br to make haloalkanes (chloro–, bromo–).
Extend the chain and add –COOH to make a carboxylic acid (–oic acid).

For each build, write the name and draw a condensed structural formula.

Examples

Ethane → Ethene → Ethyne; Propane → 1-propanol; Butane → Chlorobutane; Ethanoic acid.

Summary

You can now name straight-chain C1–C6 molecules and recognise common functional groups. This vocabulary prepares you for branching, locants, and isomerism next lesson.

Check your understanding

Name these: CH₃–CH₂–CH₃; CH₂=CH–CH₃; CH≡C–CH₃.
Which suffix would you use for an alcohol? For a carboxylic acid?
Give the general formula for alkanes and explain what “homologous series” means.

The nomenclature rules

C4.4 Organic Nomenclature Basics (Part 2): Substitution, Locants & Branching

This lesson adds precision to your naming: numbering the chain (locants), mono/di-substitution, and simple branching. You’ll practise rapidly with a Molymod Challenge.

Locants and substitution

Number it right

Choose the longest continuous carbon chain as the parent (e.g. butane, pentane).
Number the chain to give the lowest set of locants to double/triple bonds and substituents.
Apply mono-/di- prefixes (e.g. 1-chloropropane vs 1,2-dichloroethane).

Write names for teacher-provided structures, then swap: build each other’s named molecules to check accuracy.

Branching (alkyl substituents)

Branching is when the carbon chain forks into two different chains. A branch may have as few as one carbon atom.

The longest unbroken chain provides the root of the name of the compound.

Add side chains

Introduce methyl– and ethyl– substituents. Example: 2-methylpropane, 3-methylpentane.
Alphabetise different substituents; use di-/tri- for repeats (e.g. 2,3-dimethylbutane).
Redraw neatly as condensed structural formulae after checking with molymods.

Examples

1-chloropropane; 2-chloropropane; 1,2-dichloroethane; 2-methylpropane; 2,3-dimethylbutane.

Let's go over nomenclature basics again

Molymod Challenge

Name ↔ Build Race

Round A (Name → Build): Teacher calls “2-methylbutane”, “1-bromopropane”, “2-butanol”. Teams build fast, then hold up.
Round B (Build → Name): Teacher shows a model; teams write the IUPAC name with correct locants.
Round C (Isomer Sprint): “Make a different isomer of C₅H₁₂.” Bonus for neat, unambiguous condensed formulas.

Summary

You can now number chains, position functional groups, and name simple branched molecules accurately. Next, you’ll measure boiling points and connect structure to intermolecular forces.

Check your understanding

Give correct names (with locants): CH₃–CH(Cl)–CH₃ and CH₃–CH₂–CH₂Cl.
Name a different isomer of C₅H₁₂ than pentane, and draw its condensed formula.
Explain what “lowest set of locants” means and apply it to 2,3-dimethylbutane.

Activity - The Nomenclature Olympics

Each student starts with:

8 carbon atoms (black - four holes)
18 hydrogen atoms (white - one hole)
4 oxygen atoms (red - two holes)
4 chlorine atoms (green - one hole)
18 short (single) bonds
4 long (double) bonds.

Use the link below to open up the application. Enter the agreed time and click "next molecule" to start the race.

Students will go head-to-head to build the molecules displayed on the screen.

To turn off the alarm, click on the timer.

Winners go through to the next round.

The Nomenclature Olympics

C4.5 Experimental Determination of Boiling Points

This lesson introduces experimental techniques for measuring boiling points of small organic molecules. Students use the Siwolobov micro-method to measure methanol and ethanol. The data will later be extended to a homologous series of alkanes.

The Siwolobov micro-method

Practical setup

A small capillary tube, sealed at one end, is inverted into the liquid sample inside a thin-walled melting point tube.
The tube is heated gently in a water bath until a continuous stream of bubbles emerges.
The temperature is recorded when the last bubble escapes and the liquid begins to be drawn back.

Work in pairs, and record careful temperature readings for methanol and ethanol.

Accuracy and safety

Ensure steady heating — avoid superheating or rapid boiling.
Both methanol and ethanol are flammable; keep open flames away, use a hot water bath.
Compare results with literature values (methanol 65 °C, ethanol 78 °C).

Worked example

If a student records methanol b.p. as 63 °C, the % error compared to literature is:
(|63–65| ÷ 65) × 100 = 3.1 %.

Summary

You have learned how to use the Siwolobov micro-method to measure boiling points of small organic molecules. This technique provides accurate results with only a small volume of liquid and is safer than bulk boiling experiments.

Check your understanding

Explain why the capillary tube is sealed at one end in the Siwolobov method.
What is the literature boiling point of ethanol, and how does it compare to your measured value?
Suggest two possible sources of error when using this method to determine boiling points.

C4.6 Boiling Points of Alkanes and Intermolecular Forces

This lesson extends the boiling point investigation from PS7.5 to a homologous series of alkanes (C1–C8). Students collect literature values, plot a graph in Excel, and use the trend to introduce London dispersion forces (LDF).

Data collection

Student activity

Work in groups to collect boiling point data for alkanes from methane (C1) to octane (C8).
Enter values into Excel as a table: “Relative mass” vs. “Boiling point (°C)”.
Create a scatter plot with a best-fit line.
Ensure the graph has correctly labelled axes and a descriptive title.

Observing the trend

Boiling point increases with chain length.
This is due to stronger London dispersion forces as the number of electrons increases.
Branching reduces surface contact and lowers boiling point.

Worked example

Compare butane (C₄H₁₀, b.p. –0.5 °C) with octane (C₈H₁₈, b.p. 126 °C). Octane has twice as many carbons, more electrons, and stronger dispersion forces → higher boiling point.

Summary

You have observed how boiling points of alkanes increase with chain length and decrease with branching. This reflects the role of intermolecular London dispersion forces, which are stronger in larger, more extended molecules.

Check your understanding

Why do boiling points increase as the alkane chain length increases?
How does branching affect the boiling point of alkanes, and why?
Explain why London dispersion forces are stronger in octane than in methane.

C4.5 - Isomerism and Molecular Design

In this lesson you will explore how molecules with the same molecular formula can have different structures (isomers). You will use molymods to build and compare isomers, and discover how small changes in structure affect physical properties.

Structural isomers

Isomers are compounds with the same molecular formula but different structural arrangements.
Example: Butane (C₄H₁₀) exists as n-butane (straight chain) and isobutane (branched chain).
Even though the formula is the same, their boiling points differ due to branching.

Molymod challenge

In pairs, race to build all possible isomers of C4H10 (butane) and C5H12 (pentane).
Check your models against classmates — are there duplicates or missed structures?
Discuss how branching changes surface area and affects boiling points.

Designing molecules

Chemists design molecules by altering chain length, branching, and functional groups.
This structural control allows tuning of properties like volatility, solubility, and reactivity.
Isomerism is a foundation for drug design, fuels, and materials science.

Worked example

Pentane (C₅H₁₂) has three isomers: pentane, methylbutane, and dimethylpropane. Their boiling points are 36 °C, 28 °C, and 9 °C respectively. Increased branching → lower boiling point.

Summary

You have learned that isomers share the same molecular formula but differ in structure. Branching changes physical properties such as boiling point, and molecular design is a key tool in applied chemistry.

Check your understanding

What is the difference between butane and methylpropane?
Why does dimethylpropane have a much lower boiling point than pentane?
How does isomerism provide opportunities for molecular design in industry?

C4.5 - Unsaturation

Although the term suggests something to do with water, it only refers to compounds containing either double or triple carbon - cartbon bonds.

They are said to be "unsaturated" in that they are able to bond more hydrogen (or other atoms) by opening the double or triple bonds.

We have seen in the section on nomenclature that carbon carbon double bonds give molecules the suffix "-ene", and triple bonds "-yne".

The displayed structure of ethene

Physical properties

The alkenes have very similar physical properties to alkanes. The smaller members of the homologous series are volatile compounds that are gases at room temperature and after C₅H₁₀, pentene they are liquids. The alkenes do not dissolve in water to any great extent, but dissolve in non-polar solvents.

Chemical properties

Alkenes are more reactive than alkanes due to the presence of the double bond. This can be used to differentiate the two families of compounds.

Activity - Testing for unsaturation

Pour a few cm³ of bromine water into a clean test tube.

Add a few drops of hex-1-ene. Place a bung in the test tube and shake. Observe any change

To a second clean test tube with bromine water, add a few drops of hexane. Place a bung in the test tube and shake. Observe any change

How do the hexane and hex-1-ene behave with the bromine water?

Repeat the tests above using potassium manganate(VII) instead of bromine water

How do the hexane and hexene behave with potassium manganate(VII)?

Tesing for unsaturation

Activity - Making ethyne

Place a small spatula of calcium carbide into a clean boiling tube (large test tube).

Using a water bottle add a few drops of water.

Rest a rubber bung on top of the test tube (do NOT push it into the tube)

Test the gas using a lighted splint - CARE

Add a few cm³ of water to the remaining calcium carbide. Allow the reaction to subside and filter the liquid into a clean test tube.

Test the pH of the filtrate by placing one drop onto a piece of indicator paper.

Carefully use a clean straw to breathe exhaled air gently (no splashing) through the filtrate. Observe.

Now test yourself

Click on the button below to access the self-tests for MYP9 and MYP10.

MYP Self-test

Physical Science Enhancement - Chemistry 4 - Carbon the element of life

Content

Scheme of work