he believed
the model and
expected the
alpha particles
to go through
the gold foil
results - atoms are composed mainly of empty space
have an extremely positive centre
thought that there was an electron
cloud surrounding the nucleus
the arrangement of electrons
Neils Bohr - believed electrons existed
in 'energy levels' this was proofed by
the emission spectrum
types of spectra
Continuous produced by a
liquid or solid a continuous
spectrum is emitted unable to
detect the element stic
a line spectrum is produced by gaseous
matter, it is charateristic
Emission spectrum
every element gives out its own unique emission spectrum
LASERS- Light amplification by stimulated emission of radiation
Produce an intense beam of light, the
electrons recive energy and go to the same
energy level and then emit the same
wavelength photon
used to treat eye problems
used for telecommunication in optical fibers
used in welding and cutting
used in target designation
E2-E1=hxf
E2-E1 (difference in energy
levels) h= planks constant
f=frequency
c= f x ^
Bohrs theory
Radioactivity
Henri Becquerel
discovered that a
crystal of uranium was
emitting some kind of
light. Marie Curie later
went on to research
more and name this
occurance as radiation.
natural radiation - the spontaneous
decay of a nucleus, with the
emission of some form of radiation
artificial radioactivity- radioactivity from atoms
caused b nuclear bombardment
The activity of the radioactive nucleus
the number of nuclei of a radioactive sample decaying per
second= activity (A) / Becquerel (Bq)
The law of radioactive decay
no. of nuclei decaying at that
moment is proportional to the
no. undecayed @ that instant
RATE OF DECAY= ^ x N
N- the no. of undecayed atoms
^ - decay constant
each isotope has its own decay constant
the rate decreases as time goes on
Half- life (T 1/2) - the time taken for half of the undecayed atoms in an sample of the element to decay
Detecting nuclear radiation and uses
Geiger-Muller tube or solid state detector
- radiation passes through the
window of the tube and ionises
the gas - the e- are accelerated
towards the anode causing
more ionization -this induces a
small current which measures
the pulse time for each ionizing
particle -it cant tell the type of
radiation