Comparing nano scale to atoms and molecules

Bonding, structure, and the properties of matter • Bulk and surface properties

Flashcards

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Can a single molecule ever be larger than 1 nm?

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Yes; large molecules and macromolecules such as proteins or long polymers can measure several nanometres across.

Key concepts

What you'll likely be quizzed about

Definition of the nanometre and comparable units

The nanometre equals 1 × 10^-9 metres. The ångström (Å) equals 1 × 10^-10 metres and often appears when quoting atomic dimensions. Converting between units clarifies scale: 1 nm = 10 Å and 1 Å = 0.1 nm. Using these units provides appropriate resolution for atoms (Å) and nanoparticles (nm).

Typical sizes of atoms and molecules

Atomic radii typically range from about 30 pm to 200 pm (0.03–0.20 nm), depending on element and bonding. Small molecules, such as diatomic gases and simple organic molecules, usually measure about 0.1–1 nm across. Larger molecules, such as polymers and proteins, can reach several nanometres in size. Size variation depends on atomic composition, bond lengths and molecular geometry.

Definition and size range of nanoparticles

Nanoparticles commonly describe particles with at least one dimension between 1 nm and 100 nm. Because nanoparticles contain many atoms, they are larger than single atoms or simple molecules but remain too small to see with visible light. The 1–100 nm range defines when bulk material properties begin to change due to surface-dominated effects.

Cause → effect: how size affects properties

Surface area to volume ratio increases as particle size decreases. Cause: shrinking linear dimensions increase exposed surface relative to internal volume. Effect: higher fraction of atoms at the surface changes reactivity, melting point and catalytic behaviour compared with bulk material. Optical properties also change because particle size approaches the wavelength of interacting electrons or photons.

Limiting factors and measurement considerations

Measurement techniques impose limits on reported sizes. Electron microscopy and atomic force microscopy resolve down to sub-nanometre scales, while light microscopy cannot resolve individual nanoparticles. Effective size can differ from core size because of adsorbed layers, charge clouds or hydration shells, which cause measured diameters to exceed the bare atomic or core dimensions.

Key notes

Important points to keep in mind

1 nm equals 10^-9 metres; 1 Å equals 10^-10 metres.

Atoms typically measure about 0.1 nm (10^-10 m) in diameter.

Nanoparticles range from 1–100 nm; size defines when surface effects dominate.

Higher surface area to volume ratio at smaller sizes increases reactivity and alters melting points.

Effective measured size can exceed core size because of coatings or hydration shells.

Light microscopy cannot resolve nanoparticles; electron/AFM methods provide nanoscale resolution.

Large molecules can span several nanometres and overlap the lower end of the nanoparticle range.

Aggregation reduces surface area per mass and shifts behaviour toward bulk properties.

Quantum confinement affects optical and electrical behaviour in the smallest nanoparticles.

Unit choice (nm vs Å) improves clarity when describing atoms versus nanoparticles.