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B1.1.1—Carbon atom properties

Carbon forms four strong covalent bonds, allowing chains, rings, branches, multiple bonds, and functional groups that produce diverse biological molecules.

Syllabus
First assessment 2025
Objective
B1.1.1
Level
HL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceMay 2018
Most common paperPaper1
Typical marks1

Common command terms

  • Outline
  • Identify

Recent exam appearances

May 2018Paper1 ["HL"] · TZ15[ 1 ]B1.1.1—Carbon atom properties
Practice this objective

Coverage 2018–2018 · Updated 15 Jul 2026

Carbon's Four Bonds Create Biological Variety

Carbon is central to biological molecules because one carbon atom can form four covalent bonds, allowing stable chains, branches and rings.

Its four outer-shell electrons can be shared with carbon, hydrogen, oxygen, nitrogen or sulfur. Changing the carbon skeleton or attached groups changes shape and chemical behaviour, so structure can produce different biological functions.

Useful consequences:

  • carbon atoms link into chains, branches and rings
  • single and double bonds change shape and reactivity
  • large molecules can contain many different carbon arrangements

Glycogen and cellulose both contain glucose units, but their bonding arrangement gives glycogen a compact storage form and cellulose strong fibres.

Four bonds explain carbon's versatility; they do not make every carbon compound chemically identical. Always connect the particular structure to the claimed function.

Carbon atom properties

Assessment in practice

1–4 marks
How it is assessed

This objective is assessed through structured response, commonly using Outline / Identify.

Command terms

Outline / Identify

What earns marks

Build the answer around this relationship: Carbon can form four covalent bonds with carbon and other non-metal elements.

Representative question

Question 1

[Maximum number: 4]

Outline the chemical properties of carbon that allow it to form diverse compounds.

Structure To Function

B1.1 becomes easy when every answer follows structure -> property -> function. Carbon skeletons and functional groups create molecular diversity. Condensation builds larger molecules and hydrolysis breaks them. Alpha-glucose stores energy as starch and glycogen; beta-glucose forms strong cellulose. Surface carbohydrates enable recognition. Lipids are hydrophobic, triglycerides store energy, phospholipids self-assemble into bilayers, and steroids cross membranes because they are mostly non-polar.

  • Carbon bonding and functional groups explain molecular diversity.
  • Condensation releases water; hydrolysis uses water.
  • Carbohydrates can store energy, build cell walls, and mark cell surfaces.
  • Lipids are hydrophobic and not true polymers.
  • Triglycerides store energy; phospholipids form membranes; steroids signal across membranes.

Concept essentials

  • Carbon can form four covalent bonds with carbon and other non-metal elements.
  • Carbon skeletons may form chains, branches and rings.
  • Single and double bonds change molecular shape and properties.
  • Functional groups attached to carbon skeletons give biomolecules distinctive chemical behaviour.