Topic One ~ Inside an Atom
Democritus in 440BC came up with a theory that if you continued to cut particles up into smaller and smaller pieces eventually you would come to a piece of that could no longer be divided. He called this piece "atom" meaning indivisible. Thousands of years later it was discovered that these atoms could still be divided into smaller pieces which we call the structure of the atom.
In 1909 Earnest Rutherford conducted the famous Gieger-Marsdon experiment in which he concluded that the atom was mostly empty space with more than 99% it's mass located in its centre. This model predicted that the centre (nucleus). This nucleus is not a single body but is made up of at least two kinds of particles; protons (positively charged) and neutrons (negatively charged). These two particles are responsible for the bulk of the mass of an atom and are held together by a strong nuclear force, which is necessary to overcome the repulsion force of the positive charges. Around the outside of the nucleus are what is commonly referred to as shells, sitting in the predominantly empty space. In each these shells electrons (negative charged particles) orbit the nucleus. While Junior Science generally focuses on the nature of the shell structure due to its importance to Chemistry and other areas of Physics, Nuclear Physics as the name suggests is the study of the nucleus, and so is mainly concerned with what happens to protons and neutrons in atoms. Atomic Number and Mass Number
The atomic number is the number of protons in an atom. In neutral atoms this will also correspond to the number of electrons, as there must be the same number of positive and negative charges to create the overall neutral charge.
The mass number is roughly calculated by adding the number of protons and neutrons together. Electrons are not counted as they are virtually massless. When writing this in shorthand we use this structure: |
Elements and Isotopes
When a substance consists of atoms with the same atomic number (protons), they called an element. This means that they all have the same chemical properties. This allows us to easily arrange the elements into the periodic table, which provides information about similarities in chemical and physical characteristics of atoms.
Despite having the same atomic number, each element however, does not have a unique mass number as the number of neutrons within the nucleus can vary. These variations are called isotopes. Isotopes have the same chemical properties, but can have different physical properties. These isotopes can be useful in applications such as carbon dating.
Despite having the same atomic number, each element however, does not have a unique mass number as the number of neutrons within the nucleus can vary. These variations are called isotopes. Isotopes have the same chemical properties, but can have different physical properties. These isotopes can be useful in applications such as carbon dating.