atomic structure/radiation

• 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
• 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
• Atomic theory originally proposed by Democritus


  Around 500 BC
• It took another 2,300 years, meaning the 1800s, before anyone really improved on Democritus' ideas
• John Dalton


  Described atoms as solid spheres and suggested that different types of spheres might make up the different elements
• J.J. Thompson came up with the plum pudding model


  1897
• J.J. Thompson's experiments showed that atoms simply couldn't be solid spheres and instead that they must have contained negatively charged particles which we now know to be electrons</b>
• Ernest Rutherford and his students made a big discovery


  1909
• Rutherford's experiment


  1. Took positively charged alpha particles and fired them at a thin sheet of gold

  2. Some alpha particles were deflected to the side and a small number were even deflected back
• Rutherford's nuclear model


  Proposed that the positive charge of the atom was concentrated in a compact nucleus, with the negative charge existing in a cloud around this central nucleus
• Rutherford's model had one important flaw - there didn't seem to be anything stopping the cloud of negative electrons from rushing in towards the positive nucleus, meaning the atom should just automatically collapse
• Niels Bohr suggested a solution to the flaw in Rutherford's model


  1913
• Bohr's model


  Suggested the electrons orbited the nucleus in a similar way to how the planets orbit the sun, and that they were held in shells
• Bohr's model of the atom, with the electrons orbiting the nucleus, is what prevents the atom from collapsing
• Further experiments by Rutherford found that the positive charge in the nucleus is actually made up of small discrete particles which we now know as protons
• A short while later, James Chadwick provided evidence for neutral particles in the nucleus which we now call neutrons
• This is how we understand the atom today
• 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


  Each box in the periodic table representing 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)
  • Electrons can jump to higher energy levels if they gain enough energy
  • Electrons will fall back down to lower energy levels and re-emit the energy as electromagnetic radiation
• Ionization


  When an outermost electron absorbs enough energy to completely leave the atom, leaving the atom with a positive charge (a positive ion)
• Ionizing radiation is able to knock electrons off atoms and ionize them
• Isotopes


  Different forms of an element, with the same number of protons but different numbers of neutrons
• Only one or two of an element's isotopes are stable, while the rest are unstable and undergo radioactive decay</b>
• Radioactive


  Consisting of unstable isotopes that can decay
• Types of nuclear radiation


  • Alpha particles
  • Beta particles
  • Gamma rays
  • Neutrons
• Alpha particles


  • Made up of two protons and two neutrons, like the nucleus of a helium atom
  • Don't have any electrons, so have an overall charge of two plus
  • Easily stopped by collisions with other molecules, can only travel a few centimeters in air and are absorbed by a single sheet of paper
  • Strongly ionizing, can easily knock electrons off any atoms they collide with
• Beta particles


  • Just electrons, with a charge of -1 and virtually no mass
  • Emitted when a neutron in an atom decays into a proton and an electron
  • Moderately ionizing and penetrate moderately far into materials, stopped by several meters of air or about five millimeters of aluminium
• Gamma rays


  • Waves of electromagnetic radiation, often emitted after alpha or beta radiation
  • Don't have any mass or charge, tend to pass straight through materials rather than colliding with atoms
  • Weakly ionizing, can penetrate long distances through air and require thick sheets of lead or multiple meters of concrete to stop
• Neutron emission


  • Occurs when a nucleus contains too many neutrons, making it unstable, and it throws out a neutron to increase stability
• Nuclear equations for alpha, beta, and gamma radiation


  1. Alpha particles consist of two protons and two neutrons

  2. Unstable nucleus undergoes alpha decay and emits alpha particle

  3. Subtract 4 from mass number and 2 from atomic number

  4. Resulting element is different, check periodic table

  5. Add emitted helium
• Beta decay


  1. Neutron turns into proton and emits fast moving electron (beta particle)

  2. Atomic number increases by 1, mass number stays the same

  3. Represent beta particle with beta symbol and charge of -1
• Gamma radiation


  1. Pure energy, no mass or charge

  2. Does not change anything in the nucleus

  3. Represent with gamma symbol