Atomic Structure and Radioactivity Flashcards
JJ thompson’s plum pudding model
Introduced the idea of subatomic particles - the atom is a uniform, positively charged sphere containing electrons in the sphere that were negatively charged, balacing out the energy
Rutherfords Atomic model
a small, positively-charged nucleus surrounded by empty space and then a layer of electrons to form the outside of the atom
Rutherford - Bohr model
electrons orbit the nucleus in shells (energy levels)
Rutherford’s Gold Foil Experiment
Alpha-particles were directed at a thin sheet of gold foil; most passed through the foil, but a few were deflected - this led to the discovery of the atomic nucleus
what is an alpha particle
A helium nucleus
radius of an atom
1 x 10^-10m
basic structure of an atom
positively charged nucleus composed of both protons and neutrons surrounded by shells with electrons
where is the majority of the mass of an atom concentrated
the nucleus
How are electrons arranged
at different energy levels in different distances from the nucleus.
how can electrons move closer to the nucleus
emission of electromagnetic radiation, goes to a lower energy level
how can electrons move further away from the nucleus
absorption of electromagnetic radition, moves to a higher energy level.
Mass number
protons + neutrons
atomic number (proton number)
number of protons in atom. atoms of same element have same number of protons
Element
substance made of one type of atom
Isotope
atoms of same element with different amount of neutrons
proton relative mass
1
neutron relative mass
1
electron relative mass
approximately 1/2000
Nucleons
collective term for protons and neutrons. particles found in the nucleus of atoms.
proton relative charge
+1
neutron relative charge
0
electron relative charge
-1
how are atoms represented
Atomic symbol in the middle.
Mass number (A) in the top left
Atomic number (X) in the bottom left
how do atoms turn into positive ions
lose electron(s)
what were atoms thought of before the discovery of the electrons
tiny sphere that could not be divided
what did James Chadwick do
discovered the existence of neutrons within the nucleus
photon
Photons are particles that travel through the wide spaces between atoms
what does a photon represent
a particle representing a quantum of light or other electromagnetic radiation. A photon carries energy proportional to the radiation frequency
Energy associated with a single photon equation
Energy (E) = Planck’s constant (h) x frequency of radiation (f)
E = hf
What substances are said to be radioactive
substances that give out radiation from unstable nuclei all the time
Radioactive decay
Some atomic nuclei are unstable.Radioactive decay happens when the nucleus gives out radiation as it changes to be more stable.
Activity is:
rate at which a source of unstable nuclei decays.
What is activity measured in
becquerel (Bq)
Count rate is
the number of decays recorded each second by a detector
example of a count rate detector
Geiger-Muller tube
3 types of nuclear radiation
alpha particle
beta particle
gamma ray
alpha particle
consists of 2 neutrons and 2 protons, same as a helium nucleus
symbol:α
beta particle
high speed electron ejected from nucleus as neutron turns into proton
symbol:β
gamma ray
electromagnetic radiation from the nucleus
symbol:γ
properties of alpha particles
relative mass - 4
charge is +
helium nucleus
high ionisation
low penetrating power
stopped by paper or skin
short range in air
properties of beta particles
relative mass - 1/2000
charge is -
medium ionising power
medium penetrating power
stopped by aluminium
medium range in air
properties of gamma rays
relative mass - 0
no charge
type of em radiation
low ionisation
high penetrating power
stopped by lead or concrete
very long range in air
whats used to represent radioactive decay
Nuclear equations
Radioactive contamination
unwanted presence of materials containing radioactive atoms.
hazard of radioactive contamination
decay of contaminating atoms would emit radiation
Irradiation
exposing an object to nuclear radiation. Irradiated object does not become radiaoactive.
background radiation is not around us all the time. True or false
False, it is
natural sources of background radiation
rocks and cosmic rays from space
man made sources of background radiation
fallout from nuclear weapons testing and nuclear accidents
level of background radiation is affected by:
Occupation and or location
