What is matter made out of?
What is energy?
Why does the Sun shine?

It is made of atoms.

• There are 92 naturally occuring kinds of atoms. Eg
  1. H hydrogen
  2. He helium
  3. Li lithium
  4. Be beryllium
  5. B boron
  6. C carbon
  7. N nitrogen
  8. O oxygen
• Also
  • Fe iron (26)
  • the last is U uranium (92)
• Atoms are often stuck together in molecules. Eg.
  • H₂O water
  • CO carbon monoxide
  • H₂ hydrogen
• Atoms are small, about 10^-10 m in diameter for the smaller ones.

Atoms are made of electrons moving around a nucleus.

• Electrons are light particles with negative electric charge.
  • As far as one can determine by experiments, they have zero size.
• Nuclei are heavy particles with positive electric charge.
  • Experiments show that the size of a nucleus is about 10^-15 m in diameter for the smaller ones.
  • Nuclei are made of protons and neutrons.
• Positively charged particles attract negatively charged particles. That's what holds atoms together.
• In very hot places (eg. stars) the electrons can get ripped off of the atoms. An atom that is missing one or more of its electrons is called an ion.
• Here is a tour of the atomic world.

Energy is conserved.

With this knowledge about matter, we can discuss why it is a sunny day today.