Atomic structure (1) Flashcards
History of the atom:
John Dalton Billiard ball-
JJ Thompson Plum pudding-
Ernest Rutherford Nuclear model-
Bohr-
Rutherford-
Chadwick-
John Dalton Billiard ball- atoms where solid spheres
JJ Thompson Plum pudding- positively charged spheres with electrons in them
Ernest Rutherford’s Nuclear model- positive alpha particle scattering, when electrons fired through gold foil, showed that the atom was mostly empty space with a small positive nucleus surrounded by electrons
Bohr- electrons orbit on fixed energy levels
Rutherford- discovered protons
Chadwick-discovered neutrons
What is an isotope
a form of an element with a different number of neutrons
there are normally only a few stable forms
what is radioactive decay
an unstable isotope emitting particles in order to become stable
Alpha-
Beta-
Gamma-
Alpha- two neutrons and two protons, mass of 4, charge of +2
travel a few cm in air, stopped by skin and paper
highly ionising
Beta- high-speed electron, no mass, charge of -1
moderately ionising
travel a few metres in the air, stopped by aluminium
for every beta particle emitted, a neutron has turned into a proton
Gamma- electromagnetic radiation, doesn’t change the atoms charge or mass
can travel extremely long distances
partially stopped by thick lead or concrete
mildly ionising
What is the half-life of an isotope
time taken for the number of radioactive nuclei in an isotope to halve
how can radiation be measured
unit for rate of decay
using a Geiger counter, the rate of decay is measured in becquerels
examples of background radiation (4)
space- cosmic rays from the sun
radiation from nuclear bombs and waste
rocks with radon gas (granite)
hospitals
what is exposure to external radiation called
irradiation
how can radioactive objects be contained
lead-lined boxes
what is contamination
radioactive particles getting onto/into objects, which can be damaging as radioactive sources can ionise body cells
uses of radiation (2)
gamma sources can be used as medical tracers, as they don’t cause harm to the person
radiotherapy- using radiation to treat cancer by firing a weak source from multiple directions at the tumour
what is nuclear fission
what is released
what is it used for
How is it controlled
-splitting a large, unstable nucleus into smaller nuclei by firing a slow speed neutron at it, which releases a lot of energy
-3 neutrons are released by fission, which can be absorbed by another nucleus causing a chain reaction
-the energy that isn’t transferred to the kinetic stores of products is carried away by gamma rays
-this energy can be used to heat water, turning turbines to generate power
-the amount of energy released can be controlled by boron control rods
-These are lowered into the nuclear reactor to absorb neutrons and slow down the chain reaction
nuclear fusion
two smaller nuclei colliding at high speed to create a larger nucleus
the larger nucleus loses mass in the form of energy
fusion releases a lot of energy, but is unsafe currently
