-10 Atoms are very small, having a radius of about 0.1 nm (1 x 10 m).

The idea

Atoms are the fundamental building blocks of matter, but they are incredibly small. The typical radius of an atom is about 0.1 nanometres (nm). Since 1 nm = 1 × 10⁻⁹ m, this means an atomic radius is about 1 × 10⁻¹⁰ m. To visualise this, imagine lining up atoms across a 1 mm gap: because the diameter is about 0.2 nm, you would need roughly 5 million atoms to span the distance. This scale explains why we use standard form and nanometres when discussing atomic dimensions. Understanding the size of atoms is essential for appreciating why they cannot be seen with ordinary microscopes and why models are used to represent them. It also underpins concepts like atomic structure and the scale of the nucleus compared to the whole atom.

What earns the marks

• State that the typical radius of an atom is approximately 0.1 nm.
• Convert 0.1 nm to metres: 0.1 nm = 1 × 10⁻¹⁰ m.
• Recognise that atoms are extremely small, with diameters around 0.2 nm.
• Use standard form to express atomic dimensions, e.g., 1 × 10⁻¹⁰ m.
• Compare the size of an atom to everyday objects to appreciate its scale.

Common mistakes and how to put them right

• Writing the radius as 0.1 m instead of 0.1 nm.

  Put it right by remembering that nm stands for nanometre, which is 10⁻⁹ m.

• Confusing the exponent when converting.

  Put it right by multiplying 0.1 by 10⁻⁹.

• Forgetting to include units when stating the radius.

  Put it right: Include nm or m as appropriate.

Exam tips

• Memorise the approximate atomic radius in both nanometres and metres to save time in exams.
• When converting between nm and m, remember that 1 nm = 1 × 10⁻⁹ m, so multiply the number of nm by 10⁻⁹.
• Practise writing very small numbers in standard form to avoid errors with exponents.