P4- Atomic Structure Flashcards
developing the model of an atom:
-The plum pudding model
The plum pudding model was the first scientific model of the atom to describe an internal structure. It was first proposed by J. J. Thomson in 1904 following his discovery of the electron in 1897
-Rutherfords nuclear model
Ten years later, Rutherford proposed the nuclear model based on evidence from the alpha particle scattering experiment.
what are alpha particles?
1) Alpha radiation is when an alpha particle (o) is emitted from the nucleus.
An a-particle is two neutrons and two protons (like a helium nucleus).
2) They don’t penetrate very far into materials and are stopped quickly - they can only travel a few cm in air and are absorbed by a sheet of paper.
3) Because of their size they are strongly ionising.
what are beta particles?
Beta Particles are High-Speed Electrons
1) A beta particle (B) is simply a fast-moving electron released by the nucleus.
Beta particles have virtually no mass and a charge of -1.
2) They are moderately ionising. They penetrate moderately far into materials before colliding and have a range in air of a few metres.
They are absorbed by a sheet of aluminium (around 5 mm).
For every beta particle emitted, a neutron in the nucleus has turned into a proton (page 197).
amma Rays are EM Waves with a Short Wavelength
Gamma rays (v) are waves of electromagnetic radiation (p.220) released by the
) They penetrate far into materile t
what are gamma rays?
Gamma raye (7) are waves of electromagnetic radiation (p.220) released by the nucleus.
They penetrate far into materials without being stopped and will travel a long distance through sir.
what is alpha decay?
Alpha decay causes the mass number. of the nucleus to decrease by four and the atomic number. Also called the proton number.
Alpha decay ________ the charge and mass of the nucleus.
decreases
Beta decay ________ the charge of the nucleus.
increases
what is the half-life?
The half-life is the time taken for the number of radioactive nuclei in an isotope to halve.
what are the risks to using radiation?
lonising radiation can enter living cells and ionise atoms within them. This can damage the cells (which can cause things like gancer) or kill them off completely. That’s why He important that you know the precautions to take when working with any sources of radiation.
what happens if unwanted radioactive atoms get onto on into an object?
the object is said to be conteminated.
E.g. if you touch a radioactive source without wearing gloves, your hands would be contaminated.
2) These contaminating atoms might then decay, releasing radiation which could cause you harm.
Contamination is especially dangerous because radioactive particles could get inside your body.
what does the seriousness of harm from radiation depend on ?
the radiation type
