4- Atomic Structure Flashcards
What did J.J. Thompson do to develop the atom model
Came up with the plum pudding model.
Which suggests that atoms are spheres of positive charge with tiny negative electrons stuck in them
What experiment did Rutherford do in 1909
The alpha scattering experiment- firing alpha particles at a thin sheet of gold foil
What happened in the alpha scattering experiment
Most particles went straight through, some were deflected and some came straight back
What was concluded from the alpha scattering experiment
Most of the mass must be concentrated at the centre in a tiny nucleus which must also be positive. Most of the atom is just empty space
What atom model was made due to the alpha scattering experiment
The nuclear model which had a positively charged nucleus surrounded by a cloud of negative electrons
What did Neils Bohr in the development of the atom
Said that electrons orbiting the nucleus were at certain distances called energy levels.
How did James Chadwick develop the atom
Proved the existence of the neutron which proved the imbalance between the atomic and mass numbers
What is radius of the nucleus
1 x 10*-14 m
About 10,000 times smaller than the radius of the atom
What is the radius of an atom
About 1 x 10*-10
What is an isotope
Atoms with the same number of protons but a different number of neutrons
What is radioactive decay
Unstable isotopes can decay into other elements and give out radiation as they try to become more stable
What is ionising radiation
Radiation that knocks electrons off atoms, creating positive ions
What is ionising power
How easily a radiation source can knock electrons off atoms
What is an alpha particle
Two neutrons and two protons
Like a helium nucleus
What r the characteristics of alpha particles
Poor penetrating power, stopped quickly, absorbed by a sheet of paper, only travel a few cm in air
Strongly ionising
What r beta particles
A fast moving electron released by the nucleus
What r the characteristics of beta radiation
Penetrate moderately far in materials, absorbed by sheet of aluminium, travel a few meters in air
Moderately ionising
What r gamma rays
Waves of electromagnetic radiation released by the nucleus
What r the characteristics of gamma rays
Penetrate far into materials, absorbed by thick lead or metres of concrete, travel long distances in air.
Weak ionising power as they pass through rather than hitting atoms
How r nuclear equations written
Atom before decay —> atom after decay + radiation emitted
What is a key rule when writing nuclear equations
The total mass and atomic number must be equal on both sides
What happens to an atom when it emits an alpha particle
The atomic number reduces by 2 and the mass number reduces by 4
What happens to the atom in beta decay
A neutron in the nucleus turns into a proton
What happens to the atom when gamma rays are released
Nothing as it is just a way of getting rid of excess energy
What can measure the count rate of a radioactive substance
A Geiger-Muller tube and counter
What is count rate
The number of radiation counts reaching the Geiger-Muller tube per second
What is half life
The time it takes for the amount of radiation emitted by the source (count rate) to half
What is activity
The rate at which a source decays
What is activity measured in
Becquerels, Bq
1Bq is 1 decay per second
What is half life in terms of radioactive nuclei
The time taken for the number of radioactive nuclei in an isotope to halve
What does a short half life mean
Activity falls very quickly because the nuclei r very unstable and decay rapidly
What does a long half mean
Activity falls more slowly because most of the nuclei don’t decay for a long time
What graph is used to measure half life
Activity against time graph
How is half life found in a graph
Finding the time interval on the bottom axis corresponding to a halving of the activity in the vertical axis
What is background radiation
Low level radiation that is around us all the time
What does background radiation come from
Naturally occurring unstable isotopes,
Space- cosmic rays mostly from the sun,
Human activity- nuclear waste or fallout
What is radiation dose
The risk of harm to body tissues due to exposure to radiation
What is radiation dose measured in
Sieverts
The dose from background radiation is small so often measured in millisieverts
What r ways to reduce the effects of irradiation
Keeping sources in lead lined boxes, standing behind barrier or being in a different room and using remote-controlled arms
What is contamination
Unwanted radioactive atoms getting onto an object
What can be worn to reduce chance of contamination
Use gloves and tongs, protective suits
What is the most damaging radiation on the outside of the body
Gamma and beta as they penetrate the skin and can get to organs
Alpha can’t penetrate skin
What is most damaging to the inside of the body
Alpha r most dangerous because they damage a very localised area.
Beta is less damaging as it absorbed over larger area and some passes out.
Gamma goes straight out
What do low doses of radiation cause in the body
Can make cells mutate and divide uncontrollably- cancer
What do high doses of radiation cause on the body
Kills cells causing radiation sickness
What can gamma radiation be used for
Medical tracers,
Radiotherapy,
Leaky pipes locating
What is nuclear fission
Used to release energy from large and unstable atoms by splitting them into smaller ones
What is formed and released in fission
Two new light elements and two or three neutrons
How do nuclear weapons work
Uncontrolled fission chain reactions that lead to lots of energy being released as an explosion
What is nuclear fusion
Two light nuclei collide at high speed and join to create a larger, heavier nucleus.
Releases a lot more energy than fission
Why haven’t scientists made fusion reactors
The temperatures and pressures needed are so high that the reactors would be very expensive and hard to build
