electrons atoms and that Flashcards
what is an ion
same atom but gained or lost an electron
what is mass number
proton + neutrons (the bigger number )
what is the atomic number
proton number
if an atom looses an electron it has what charge overall
positive charge
what is an isotope
atom of the same element with the same number of protons but a different number of neutrons so a different mass number
if sodium atoms emit light what would cause light to be emitted from a sodium atom
electrons falling to a lower energy level
discovery of nucleus
1804: John Dalton agreed with Democritus that matter was made up of tiny atoms (spheres ) that couldn’t be broken up but he thought each element was made up of diff type of atoms
2) nearly 100 years later JJ Thomson discovered particles called electrons that could be removed from atoms. he suggested atoms were spheres of pistols charge with tiny electrons which duck to them like fruit in a plum (plum pudding model )
3) in 1909 - Ernest Rutherford tried firing beans of positively charged alpha particles at thin pieces of gold foil - alpha scattering experiment. he expected the particles to pass through the gold sheet and some be deflected only a few, however most of particles did go straight through some were deflected back the way they xame
4) Niels Bohr said that electrons orbiting the nucleus do so in certain distances called energy levels. his theorteitcal calculations agreed with experimental data.
5) in 1932 James Chadwick provided existence of neutron which explained imbalance between atomic and mass number
what is radioactive decay
the unstable isotope nuclei want to become stable. therefore decay into other elements and give out radiation.
what is beta particles in radiation
- fast moving electron
- penetrate moderately into materials
- every beta particle emitted neutron turns into proton
- travel a few meters in air and absorbed by a sheet of aluminum
what are gamma rays in radiation
- weakly ionizing
- waves of electromagnetic radiation
- penetrate far into materials
- travel a long distance through air. absorbed by thick sheets of lead / concrete
alpha particles in radiation
- strongly ionizing
- don’t penetrate very far into materials
- only travel a few cm in air and absorbed by a sheet of paper
- alpha particle emitter from the nucleus made of 2 protons and 2 neutrons
definition of ionizing
ability to knock electron off an atom. alpha is highly ionizing whereas gamma is least
what is half life
time it takes for the number of nuclei of the isotope in a sample to half
(half the y- axis)
what happens to structure of an atom when the atom is ionized
less electrons as they are dispersed in ionizing
a teacher sets up a demonstration of the penetration properties of alpha , beta and gamma radiation
what are rwo safety precautions the teacher should take in demonstration
don’t point it at direction of people
wear goggles
