P4 Atomic structure

• In 1804, what did John Dalton and Democritus agree that matter was made up of?

  tiny spheres that couldn't be broken up
• what did he reckon each element was made up of?

  different types of 'atom
• nearly 100 years later, what did JJ Thompson discover?

  particles called electrons that could be removed from atoms
• what did Thompson suggest atoms were?

  spheres of positive charge with tiny negative electrons stuck in them - the plum pudding model
• in 1909, what did scientists in Rutherford's lab do?

  tried firing a beam of alpha particles at thin gold foil - the alpha scattering experiment
• what did they expect based off of the plum pudding model?

  the particles to pass straight through the gold sheet or slightly deflected
• although some particles did go straight through the sheet. what happened to the others?

  some were deflected more than expected and a few were deflected back the way they came
• because a few particles were deflected back, what did scientists realise?

  most of the mass of the atom must be concentrated at the centre of the nucleus, this nucleus must also have a positive charge since it repelled the positive alpha particles
• because nearly all the alpha particles passed straight through, what else did they realise?

  most of an atom is just empty space
• what model resulted from the alpha particle scattering experiment?

  the nuclear model
• what was the nuclear model?

  a positively charged nucleus surrounded by a cloud of negative electrons
• what did Niels Bohr state about electrons?

  electrons orbiting the nucleus do so at certain distances called energy levels
• what did evidence from further experiments change?

  the model to have a nucleus made up of a group of particles - protons - which all had the same positive charge that added up to the overall charge of the nucleus
• in 1932, what did James Chadwick prove?

  the existence of a neutron, which explained the imbalance between atomic and mass numbers
• In the current model of the atom, what does the nucleus contain?

  protons and neutrons
• what is the overall charge of the nucleus?

  positive
• How much smaller is the radius of the nucleus compared to the rest of the atom?

  about 10,000 times smaller
• What is the rest of the atom?

  mostly empty space
• what do the negative electrons do

  They whizz round the outside of he nucleus really fast.
• what is the radius of an atom?

  about 1 x 10^-10 metres
• TRUE OR FALSE: number of protons = number of electrons


  true
• what can electrons in energy levels do?

  move within or sometimes leave the atom.
• how could they gain energy?

  absorbing EM radiation
• what happens if they gain energy?

  they move to a higher energy level, further from the nucleus
• what happens if they release EM radiation

  they move to a lower energy level, closer to the nucleus
• what happens if one or more outer electrons leave the atom?

  the atom becomes a positively charged ion
• What is the atomic number?

  number of protons
• What is the atomic mass?

  Number of protons and neutrons
• what are isotopes of an element?

  atoms with the same number of protons but different number of neutrons
• all elements have different isotopes, but how many stable ones are there usually?

  one or two
• what do the other unstable isotopes tend to do?

  decay into other elements and give out radiation as they try to become more stable
• how do they become more stable?

  they try to balance the number of neutrons and protons in the nucleus or get rid of any excess energy
• what is this process called?

  radioactive delay
• what do radioactive substances do?

  spit out one or more types of ionising radiation from their nucleus
• what are the 3 types of ionising radiation you need to know?

  alpha, beta and gamma
• what else can radioactive substances do?

  release neutrons when they decay to rebalance the number of protons and neutrons
• what is ionising radiation?

  Radiation that knocks electrons off atoms, creating positive ions
• what is the ionising power of a radiation source?

  how easily it can knock electrons off atoms
• what is alpha radiation?

  When an alpha particle is emitted from the nucleus
• what is an alpha particle?

  2 protons and 2 neutrons