Atoms

Atoms

1. What does atoms contain

   • Nucleus
     • It is in the middle of the atom
     • It contains protons and neutrons.
     • The nucleus has a radius of around 1 x 10 -14 m.
     • It has a positive charge because of the protons
     • Almost the whole mass of the atom is concentrated in the nucleus
   • Electrons
     • Move around the nucleus in the electron shells.
     • They're negatively charged and thin, but they river a lot of space.
     • The volume of their orbits determines the size of the atom.
     • Electrons have virtually no mass

2. Number of protons equals number of electrons

   • Atoms are neutral - they have no charge overall (unlike ions)
   • This is because they have the same number of protons as electrons
   • The charge on the electrons is the same size as the charge on the protons, but opposite - so the changes cancel out
   • in an ion the number of protons doesn't equal the number of electrons. This means it has an overall charge. For example, an ion with a 2-charge, has two more electrons than protons.

3. Atomic number and mass number

   • The nuclear symbol of an atomic (proton) number and mass number