History

• 1897 - Thompson discovered the electron and the proton

• 1909 - Rutherford discoverd the void and a few years later the nucleous.

Structure

• atoms consist of 3 subatomic particles: protons, neutrons and electrons

• a single atom is so small that it cannot be weighted on a balance, therefore with the use of the mass spectometer relative atomic masses to the atom of Carbon can be found.

• Each atom is electrically neutral, it has no overall electric charge, in each atom infact there must be the same amount of protons and electrons.

• Proton/Atomic number (Z): number of protons in an atom (and number of electrons in an atom)

• Nucleon/Mass number (A): number of protons + neutrons in an atom

• Number of electrons is usually the same of the number of protons that never changes

• Number of electrons: nucleon number - proton number (A-Z)

• Relative Atomic Mass (Ar): this value is an average mass that takes into account the proportions of all the naturally occuring isotopes. This is also the reason why most relative atomic masses are not whole numbers. The only mass that is precise is the one of Carbon 12 that has the exact mass of 12 units. For example, the relative atomic mass of chlorine is 35.5 rather than a whole number. This is because chlorine contains two different isotopes, chlorine-35 and chlorine-37.

In the periodic table

• • The proton number increases by 1 when you go to the right

  • When you go one element down, you increase proton number by 8 in the first 3 periods (transition elements not included)

Isotopes

• atoms of same element with different number of neutrons. They have same chemical properties but different physical ones compared to normal atoms of an element. Some isotopes are unbalanced and therefore have an instable nuclei. This breaks up spontaneously and can emit certain types of radiations, these are called radioisotopes.

• • E.g. Carbon 12 and Carbon 14.

  • Two types: non-radioactive isotopes and radioactive-isotopes which are unstable atoms that break down giving radiations

  • Medical use: cancer treatment (radiotherapy) – rays kill cancer cells using cobalt-60

  • Industrial use: to check for leaks – radioisotopes (tracers) added to oil/gas. At leaks radiation is detected using a Geiger counter.