Nuclear Notation

• Nuclear Notation

  Properties of Atoms

  • The atom is made up of:
  • Protons - positively charged particles with a relative atomic mass of one unit, found in the nucleus
  • Neutrons – no charge, and also with a relative atomic mass of one unit, found in the nucleus
  • Electrons – negative charge with almost no mass (1/2000 the mass of a proton or neutron)
• • The properties of each of the particles are shown in the table below:

  
• • Although atoms contain particles of different charge, the total charge within an atom is zero
  • This is because the number of electrons is equal to the number of protons
  • For example, the following table sets out the calculation of the total charge in the Lithium atom:

  
• Atomic Number

  • The number of protons in an atom is called its atomic number (it can also be called the proton number)
  • Elements in the periodic table are ordered by their atomic number
  • Therefore, the number of protons determines which element an atom is
  • The atomic number of a particular element is always the same
  • For example:
  • Hydrogen has an atomic number of 1. It always has just one proton
  • Sodium has an atomic number of 11. It has 11 protons
  • Uranium has an atomic number of 92. It has 92 protons
• Atomic Number

  • The atomic number is also equal to the number of electrons in an atom
  • This is because atoms have the same number of electrons and protons in order to have no overall charge
• Mass Number

  • The total number of particles in the nucleus of an atom is called its mass number
  • The mass number is the number of protons and neutrons in the atom
  • The number of neutrons can be found by subtracting the atomic number from the mass number

  Number of Neutron = Mass Number - Atomic Number

  • For example, if a sodium atom has a mass number of 23 and an atomic number of 11, then the number of neutrons would be 23 – 11 = 12
• Nuclear Notation

  • The mass number and atomic number of an atom are shown by writing them with the atomic symbol
  • This is called nuclear notation
  • Here are three examples:

  
• Nuclear Notation

  • The top number is the mass number
  • This is equal to the total number of particles (protons and neutrons) in the nucleus
  • The lower number is the atomic number
  • This is equal to the total number of protons in the nucleus
  • The atomic and mass number of each type of atom in the examples above is shown in this table: