atomic structure Flashcards
(46 cards)
what was john Dalton idea of the atom?
ohn Dalton suggested that atoms where solid spheres
- he also suggested that the different types of spheres made up the different elements
what was jj Thompson theory
- discorvered particles called electrons that could be removed from atoms to daltons theory wasnt quite right
- made the plum pudding model - spheres of positive charge with tiny negitive electrons stuck in them
what happened in the alpha scattering experiment
- rutherford fired beam of alpha particles at a thin gold foil
- for plum pudding model atoms had to pass straight through.
- although most did go straight through, more were dflected than expected and some went backwards - which was something the plum pudding kodel couldnt explain
what did rutherford find out as a result of alpha scattering experiment
- that most of the mass of the atom was concentrated at the centre in a tiny nucleus - nucleus must also have positve charge as it deflected the positive alpha particles
- also realised most of the atom was just empty space as nearly all of the alpha particles whent straight through - first nuclear model
what did niels bohr suggest
there was nothing stopping the cloud of negative charge rushing into the nucleus which would make the atom collapse
he suggested that negativity charged electrons orbit the nucleus in shells.
the orbiting of the electrons prevents the atom from collapsing
what did Rutherford suggest for the second time
- Rutherford suggested that the nucleus was made up of small discrete particles know as protons
what did James Chadwick suggest
- he provided evidence that the nucleus also contained neutral particles which we know as neutrons
what is the order of the history of the atom
- atomic theory - Democritus
- solid spheres - dalton
- plum pudding model - jj
- nuclear model - Rutherford
- niels Bohr - electrons orbiting
- protons - Rutherford
- neutrons - chadwick
how can electrons move within the atom
if they gain energy by absorbing EM radiation they move to a higher energy level, further from the nucleus
if they release EM radiation then they move to a lower energy level,closer to the nucleus
what happens to the unstable isotopes
they tend to decay into other elements and give radiation as they try to become more stable - this is called radio active decay
what do radioactive substances release
- one or more types of ionising radtion from their nucleus
- they can also release nuetrons when they decay
what is ionising radition
is radiation that knocks electrons off atoms, creating positive ions
- the ionising power of a radition source is how easily it can do this
what are alpha particles
helium nuclei
they are two protons and two neutrons ( same as helium nuclei)
what is alpha radiation
when alpha particles are emitted from the nucleus
what do aplha particles do
they dont penetrate very far into materials and are stoppd quickly - they can only travel a few cm in the air and are absorbed by a sheet of paper
- becuase of teh size they are strongly ionising
how is alpha radiation used in the home
- used in smoke detectors - ionises air particles causing a current to flow. if there is smoke in the air it binds to the ions which disrupts the current a signals the alarm
what are beta particles
fast moving electrons released by the nucleus.
they are virtually no mass and a charge of -1
what do beta particles do
- moderately ionising due to their size
- they penerate moderatley far into materials before colliding
- a range in the air of a few metres
- they are absorbed by a thin sheet of aluminum
- for every beta particle emitted a neutron in the nucleus turns into a proton
how can beta radition be used in teh real world
beta emitters are used to test the thickness of sheets of metal as the particles are not immediately absorbed by material like alpha radiation adn do not penetrate as far as gamma rays
- so slight variations in thickness affect teh amount of radition passing through them
what type of rays are gamma rays
they are waves of electromagnetic raidtion released by the nucleus
what do gamma rays do
they penetrate for into materials without being stopped and will travel a long distance in the air
- this means they are weakly ionising as they tend to pass through rather than collide with atoms - eventually they hit something and cause damage
- they can be absorbed by thick sheets of lead or metres of concrete
what happens to a atoms mass number and atomic number when they release alpha particles
its atomic number reduces by two and its mass number reduces by 4 as alpha particles are made up of 2 neutrons and 2 protons
what does alpha decay do
decreases the charge and mass of the nucleus
what does beta decay do
increase the charge of the nucleus
