Drawing Diagrams in Chemistry Exams

Diagrams account for a significant portion of marks across 0620, yet many students treat them as optional extras rather than mark-earning answers. A correct diagram with clear labels can earn 3-4 marks in a single question. A missing or unclear diagram earns zero. This guide covers the five types of diagram the exam requires and the specific details each one must include.

Apparatus diagrams

Apparatus diagrams appear on Paper 4 (describing experiments) and Paper 6 (planning investigations). The marks are awarded for including the correct equipment, showing it connected correctly, and labelling it.

General rules

• Use a ruler for straight lines (flask walls, delivery tubes, clamp stands).
• Draw in 2D cross-section, not 3D. The exam expects the standard textbook style.
• Label every piece of equipment and every chemical. Use straight lines from the label to the apparatus, not arrows curving all over the diagram.
• Show the stopper or bung if the apparatus is sealed.
• Show water level in collection troughs, gas jars, and measuring cylinders.

Gas collection setups

Three methods, each suited to different gases:

Over water (downward displacement of water): Use for gases that are insoluble or only slightly soluble in water (hydrogen, oxygen). Draw a delivery tube from the flask into a trough of water, with an inverted measuring cylinder or gas jar filled with water collecting the gas.

Upward delivery (collecting a dense gas): Use for gases denser than air (carbon dioxide, chlorine). The gas jar sits upright with the delivery tube going to the bottom. Gas fills from the bottom, displacing air upwards.

Downward delivery (collecting a gas lighter than air): Use for gases less dense than air (hydrogen, ammonia). The gas jar is inverted with the delivery tube going to the top of the inverted jar.

The mark scheme checks that you have chosen the correct method for the named gas and drawn the apparatus in the right orientation.

Distillation apparatus

The key components, each worth a mark:

1. Flask containing the mixture, heated with a Bunsen burner or water bath.
2. Thermometer at the top of the flask (bulb at the side-arm level).
3. Condenser connected to the side arm, angled downwards.
4. Cold water flowing into the bottom of the condenser and out of the top.
5. Collecting beaker at the end of the condenser.

The water flow direction (in at the bottom, out at the top) is a specific mark. Drawing it reversed is a common error.

Dot-and-cross diagrams

These diagrams show how atoms bond by transferring or sharing electrons. The exam awards marks for specific features.

Ionic bonding diagrams

Marks awarded for:

• Correct number of electrons in the outer shell of each atom before transfer.
• Electrons shown transferring to the correct ion (dots for one element, crosses for the other).
• Square brackets around each ion.
• Correct charge on each ion (Na+, Cl-, Mg2+, O2-).

Common errors:

• Missing square brackets (loses 1 mark every time).
• Wrong number of electrons transferred (Mg loses 2, not 1; O gains 2, not 1).
• Showing inner shell electrons when only outer shell is required.

Covalent bonding diagrams

Marks awarded for:

• Correct number of electrons in the outer shell of each atom.
• Shared pairs shown in the bonding region between atoms.
• Correct number of bonds (O=O is a double bond, N is triple in N2).
• Lone pairs shown if requested.

Common errors:

• Drawing too many shared pairs (hydrogen shares one pair, not two).
• Not showing the lone pairs on oxygen or nitrogen when asked.
• Drawing bonds between atoms that should not be bonded (e.g., H-H bonds in water instead of H-O bonds).

Energy level diagrams

These show the energy changes during a reaction. The marks are:

1. Reactants and products labelled at the correct relative energy levels (1 mark).
2. Exothermic: products lower than reactants. Endothermic: products higher than reactants (1 mark).
3. Energy change labelled with an arrow showing the direction and the correct label (enthalpy change or delta H) (1 mark).
4. Activation energy (if asked): a hump above the reactants level, with the height from reactants to the top labelled as activation energy (1 mark).
5. Catalyst effect (if asked): a second, lower hump on the same diagram (1 mark).

Draw the diagram large enough to label clearly. A tiny sketch with cramped labels loses marks because the examiner cannot read it.

Particle diagrams

Particle diagrams show the arrangement and spacing of particles in solids, liquids and gases.

Solid: Equal-sized circles arranged in a regular, closely packed pattern. Neat rows and columns. Liquid: Equal-sized circles close together but arranged irregularly, no neat pattern. Gas: Equal-sized circles far apart with large, irregular spacing.

The marks: regular arrangement for solid (1), close but irregular for liquid (1), far apart for gas (1). The circles must be the same size for a pure substance.

Displayed formulae (organic chemistry)

A displayed formula shows every atom and every bond explicitly. No bonds are implied.

Rules:

• Every C-H bond is drawn as a line.
• Every C-C bond is drawn as a line.
• Double bonds are drawn as two parallel lines.
• Functional groups (OH, COOH, C=C) must be drawn correctly with all bonds shown.

Common errors:

• Drawing CH3 as a single unit without showing the three C-H bonds (acceptable in a structural formula but not a displayed formula).
• Drawing a single line for a double bond.
• Not drawing bonds to hydrogen atoms on oxygen (the O-H bond in alcohols must be shown).

Exam strategy for diagrams

1. Read the question to identify what type of diagram is required. “Draw the apparatus” is different from “draw a dot-and-cross diagram.”
2. Draw large. Small diagrams are hard to label and hard for the examiner to mark.
3. Label with straight lines, not arrows. Labels should be outside the diagram pointing in.
4. Use a pencil first if you are unsure. You can go over it in pen once you are confident.
5. Check your diagram against the mark scheme in your head. For apparatus: is every piece labelled? For dot-and-cross: are the brackets and charges there? For energy levels: is the arrow direction correct?

If diagram marks are being lost consistently, the fix is usually about knowing which details the mark scheme requires rather than about drawing skill. A trial lesson can identify the specific features you are omitting and drill them until they become automatic.