Atomic structure

• Atom


  The simplest particle of an element that can exist on its own
• Atomic structure


  • Atoms are made up of three subatomic particles - protons, neutrons and electrons
  • Protons and neutrons are found in the nucleus
  • Electrons orbit the nucleus in shells
• Electrons are very small compared with protons and neutrons
• Protons and electrons have equal number but opposite charge
• Neutrons do not have a charge
• Subatomic particles


  • Proton
  • Neutron
  • Electron
• Table 1.1 gives the relative masses and charges of the three subatomic particles
• An incomplete form of Table 1.1 is often given in exam questions
• The most common mistakes are giving 0 as the relative mass of an electron and writing the relative charge of a proton as +1 instead of +1 and of an electron as - instead of -1
• Atomic number


  The number of protons in the nucleus of an atom
• Mass number

  The total number of protons and neutrons in the nucleus of an atom
• Determining numbers of subatomic particles

  1. Number of protons = atomic number

  2. Number of neutrons = mass number - atomic number

  3. Number of electrons = number of protons (in a neutral atom)
• Isotopes


  Atoms that have the same number of protons (so they are atoms of the same element), but they have a different number of neutrons (so they have a different mass number)
• Isotopes of the same element have the same chemical properties because they have the same number of electrons in the outer shell
• Ion


  A charged particle
• Cation


  A positive ion
• Anion


  A negative ion
• Formation of simple ions

  1. An atom loses or gains electrons to achieve a full outer shell (the electronic configuration of the closest noble gas)

  2. The overall charge on an ion depends on the number of positive protons and the number of negative electrons
• Simple positive ions


  Have the same name as the atom from which they are formed
• Simple negative ions


  Change their ending to '-ide'
• There are two main types of examination question on ions: those that ask you to determine the number of each subatomic particle in an ion, and those that ask you to work out the formula of the ion, including its charge, from the number of subatomic particles