CC3 Atomic Structure

• • There is a nucleus at the centre of each atom.
  • This contains protons and neutrons.

  Electrons orbit the nucleus in energy shells.
• • All atoms are neutral overall as they have the same number of positive protons as negative electrons.

  Most of the mass is concentrated in the nucleus. Electrons have a very small mass.
• mass number - tells us the total number of protons and neutrons in the nucleus.
• atomic number - tells us the number of protons (AND the number of electrons).
• Atoms are so light they cannot be weighed in grams. So, we use the relative atomic mass (Ar).
• An isotope is an atom with the same number of protons and electrons, but has a different number of neutrons.
• isotope calculation = multiply atomic number with percentage, add to others, divide by 100
• electron = mass negligible, -1
• proton = mass 1, +1
• neutron = mass 1, charge 0 or neutral