Atoms

Atoms

1. The nucleus of an atom

   • In the middle of the atom
   • contains protons and neutrons
   • has a positive charge because of the protons
   • almost the whole mass is concentrated in the nucleus

2. The electrons in an atom

   • Move around the nucleus in electron shells
   • Negatively charged
   • Are tiny but cover a lot of space
   • The volume of their orbits determines the size of the atom
   • Have virtually no mass

3. Protons, neutrons and electrons

   • Protons are heavy and positively charged
     • The number of protons equals the number of electrons
   • Neutrons are heavy and neutral
   • Electrons are tiny and negatively charged

4. The mass number and atomic number

   • Mass number = total no. protons and neutrons
     • This is always the biggest number
   • Atomic number - number of protons