Atomic Structure Flashcards
What are the 3 sub-atomic particles?
Protons, neutrons, electrons
What are the relative masses of sub - atomic particles?
P-1
N-1
E-0.0005
What is the relative charge of each subatomic particle?
P - +1
N - 0
E - -1
Typical radius of an atom?
1 x 10*-10 metres
Size of nucleus compared to atom?
10,000 times smaller
Where is most of the mass of an atom concentrated?
The nucleus
When might electron configuration change?
When they interact with EM radiation
What is an isotope?
All atoms of the same element that have the same number of protons but different neutrons
What is the mass number?
neutrons and protons
What is the atomic/proton number?
Number of protons
What happens if an electron gains enough energy?
It can leave the atom to form a positive ion
Order of scientists in particle model discoveries?
1800 - John Dalton
1897 - JJ Thomson
1911 - Rutherford
1913 - Bohr
Dalton
Said everything was made of tiny spheres that couldn’t divide
JJ Thomson
Discovered the electron - plum pudding model
Rutherford
Realized most of the atom was empty space - gold foil experiment
Rutherford model
Positive nucleus at centre of atom with negative electrons around
Bohr
Electrons exist in fixed ‘orbitals’ and nucleus is made of protons and neutrons
Why do some nuclei give out radiation?
To become more stable - radioactive decay
What does radioactive activity mean?
The rate at which a source of unstable nuclei decays.
What is count rate?
number of decays recorded by a detector per second
Forms of decay?
Alpha, beta, gamma, neutrons
Alpha decay
Helium nucleus, Highly ionising, weakly penetrating 5cm of air
Bate decay
Electron, medium ionising, medium penetration 50 cm of air, sheet of paper
Gamma decay
Radiation, low ionising, highly penetrating, few cm of lead.
What is half life?
The time taken for half the nuclei of a sample to decay or count rate to half
When a nucleus decays cannot be
predicted
Equation for net decline?
(initial number - number after x half lives)/ initial number
What is contamination?
The unwanted presence of radioactive atoms on other materials and lasts for a long time
What is irradiation?
Exposing an object to nuclear radiation, but doesn’t make it radioactive lasts a short time
What is background radiation?
weak radiation that can be detected from natural / external sources.
What are some sources of background radiation?
Cosmic rays, underground rocks, nuclear fallout, medical rays
What are some uses of radiating atoms?
Medical tracers (technetium), chemotherapy to kill cancerous cells.
What is nuclear fission?
the splitting of a large and unstable nucleus
Spontaneous fission is rare
Usually, the unstable nucleus must absorb a neutron
What is the process of fission?
Unstable nuclei absorbs a neutron, it splits into two smaller nuclei, roughly equal in
size and it then emits two or three neutrons and gamma rays.
- Energy is released by the fission reaction.
- This neutron may collide with another radioactive nucleus.
- This nucleus absorbs the neutron and becomes unstable
- This nucleus splits, releasing another neutron and produces more energy
- This is a chain reaction, as energy is being released and one ‘split’ causes another to occur
What happens if the fission chain reaction is not controlled?
It will exponentially increase causing nuclear weapons
What is nuclear fusion?
when 2 small nuclei fuse to form a heavier nucleus, this releases lots of energy
Name a natural fusion reactor?
The sun
