Topic 4 - atomic structure

• Atomic theory


  The idea that everything is made up from tiny little particles that can't be broken down any further and that they're separated from each other by empty space
• Democritus proposed atomic theory

  Around 500 BC
• Atoms (according to Dalton)


  Solid spheres, different types of spheres make up different elements
• Plum pudding model (J.J. Thomson)


  Atom is a general ball of positive charge with discrete electrons stuck in it
• Rutherford's gold foil experiment

  1. Fired positively charged alpha particles at a thin sheet of gold

  2. Some alpha particles were deflected to the side or back, proving the plum pudding model wrong
• Rutherford's nuclear model


  Atom has a compact nucleus containing positive charge, with negative charge in a cloud around it
• Rutherford's nuclear model


  Had a flaw - the negative electrons should collapse into the nucleus
• Bohr's model


  Electrons orbit the nucleus in shells, preventing the atom from collapsing
• Further experiments by Rutherford found the positive charge in the nucleus is made up of protons
• Chadwick provided evidence for neutral particles in the nucleus, which we now call neutrons
• Atom


  The fundamental unit of an element, consisting of a nucleus containing protons and neutrons, and electrons that orbit the nucleus
• Nucleus


  • Contains protons and neutrons
  • Protons are positively charged
  • Neutrons are neutral
  • Protons and neutrons have a relative mass of 1
• Electrons


  • Orbit the nucleus
  • About 2000 times smaller than protons or neutrons
  • Have a negative charge of 1-
• Periodic table


  A tabular arrangement of the chemical elements, ordered by their atomic number, electron configuration, and recurring chemical properties
• Nucleus symbol


  A box on the periodic table that represents a particular element
• Nucleus symbol


  • Contains the elemental symbol
  • Atomic number (number of protons)
  • Mass number (total protons and neutrons)
• The number of protons and electrons in an atom is the same
• Isotopes


  Atoms of the same element with the same number of protons but different numbers of neutrons
• Generally only one or two of an element's isotopes are stable, the others are unstable and undergo radioactive decay
• Electrons


  • Arranged in a series of energy levels (shells)
  • Shells get progressively further from the nucleus and increase in energy level
  • Electrons can jump to higher energy levels if they gain enough energy (become excited)
  • Electrons will then fall back down and re-emit the energy as electromagnetic radiation
• Ionization


  When an electron completely leaves an atom, leaving the atom with more protons than electrons and a positive charge (a positive ion)
• Ionizing radiation is able to knock electrons off atoms and ionize them