Flashcards in module 4 Deck (21):
What did John Dalton Dalton and Democritus agree on?
matter was made up of tiny spheres (atoms) that couldn't be broken up, be Dalton thought each element was made from different types of atoms.
What did J.J. Thomson discover?
electrons, these could be removed from charge. Dalton's theory wasn't quite right. Thomson suggested atoms were spheres of positive charge with tiny negative electrons stuck in them-plum pudding model
What did Rutherford discover?
he fired alpha particles at thin gold foil-alpha scattering experiment. From plum pudding model expected them all to go through sheet or slightly deflected. Most went through some more deflected more than expected, few deflected back the way they came. Plum pudding model proved wrong.
How did Rutherford's experiment change the shape of the atom?
due to some alpha particles coming back scientist knew most mass of atom was concentrated in centre in tiny nucleus. Nucleus had positive charge since repelled positive alpha particles. Because nearly all went through most of atom was empty space-first nuclear atom
How did the atom look after Rutherford?
positively charged nucleus surrounded by cloud of negative electrons.
What did Niels Bohr discover?
electrons orbiting nucleus do it in certain distances called energy levels. His theoretical calculations agreed with experimental data. After Bohr further experiments found protons subatomic particle to make the nucleus positively charged.
What did James Chadwick discover?
proved existence of proton explained imbalance between atomic and mass numbers.
What does the current model of an atom look like?
the nucleus' radius is 10,000 times smaller than the atom. radius of atom is 1*10 to the power of -10 m. if electrons gain energy by absorbing EM radiation have to move to higher energy level far from nucleus (oppsite with other way round).
What is the atomic number?
number of protons.
What is an isotope?
an atom with different number of neutrons, all elements have different isotopes usually 1 or 2 stable ones. unstable decay and try to become stable by emitting radiation=radioactive decay. spit out 1 or more types of ionising radiation form nucleus, also release neutrons when decay. ionising radiation=radiation that knocks off electron-positive charged.
What is ionising power?
of radiation source is how easily it can knock off electrons.
How do alpha particles work?
emitted from nucleus. 2 protons and 2 neutrons. Don't penetrate far into materials stopped quickly. Can only travel a few CMs in air can be absorbed by paper. Large-most ionising. Used in smoke detectors. ionises air particles causes current to flow. Smoke-binds to ions, current stops and alarm sounds.
How do beta particles work?
fast moving electron. moderately ionising, penetrate moderately far into materials before colliding-range=few Meters. absorb by aluminium (5 mm thick). Per beta particle neutron turns to proton in nucleus. Used to test thickness of sheets of metals.
How do gamma rays/EM waves work?
electromagnetic radiation released by nucleus, penetrate far, have long range. weak at ionising tend to pass through than collide, eventually hit and do damage. Absorbed by thick sheets of lead or meters of concrete.
What are nuclear equations?
showing radioactive decay by using element symbols written: atom before decay=atom after decay+radiation emitted. Total mass and atomic numbers must be equal on both sides.
What is alpha decay?
atomic number reduces by 2 and mass number reduces by 4. proton is positive neutron is neutral so charge decreases. equation wirtten as helium nucleus top:4 bottom:2 He
When are gamma rays sometimes emitted?
When a nucleus decays by alpha or beta decay.
What is beta decay?
protons increase by 1-increase positive charge by 1. Nucleus lost electron but gained proton so no mass changes.
How does gamma decay work?
Gamma rays are a way of getting rid of excess energy from a nucleus. There is no change of the atomic mass or atomic number of an atom.
What is a radioactive substance and how do you measure radiation?
A substance that gives out radiation from nuclei of their atoms. Measured with Geiger-Muller tube and counter, records count-rate, number of radiation counts reaching per second.