3.1.2

Atom Size

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Atoms and Sub-Atomic Particles

An atom is made up of a positively charged nucleus surrounded by negatively charged electrons. Atoms are tiny and very light. They are made up of sub-atomic particles (protons, neutrons, and electrons), which are even smaller and lighter than an atom.

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How big are atoms?

  • The radius of atoms is approximately 0.1 nanometres, or 1x10-10 m.
    • About 5 million hydrogen atoms could fit into a pinhead.
  • The nucleus of an atom is 10,000 times smaller than the atom. Most of an atom's mass is concentrated in the nucleus.
    • If an atom was the size of Wembley Stadium, then the nucleus would be the size of a garden pea.
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Relative mass

  • Sub-atomic particles:
    • Relative mass of protons and neutrons = 1.
    • Relative mass of electrons = 0.0005 (this gets rounded to zero).
  • Atoms:
    • Relative mass = number of protons + number of neutrons.

Jump to other topics

1States of Matter

2Elements, Compounds & Mixtures

3Atomic Structure

4The Periodic Table

5Chemical Formulae, Equations & Calculations

6Bonding

7Electrolysis

8Groups of the Periodic Table

9The Atmosphere

10Reactivity Series

11Metal Extraction

12Acids & Alkalis

13Chemical Tests

14Physical Chemistry

15Organic Chemistry

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