Atom Size
Chemistry: Edexcel IGCSE, topic 3.1.2
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.
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.
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.
Test yourself on Atom Size
What is the relative mass of an electron?
What is the average radius of atoms?
Which sub-atomic particle does NOT have a relative mass of 1?
Can you remember the 2 analogies that helped show how small atoms and sub-atomic particles are?
In what environment would the relative mass of an atom change?