P1 - Atomic Structure Flashcards
What happened to the theory of the atom in 1804 ?
John Dalton theorised that atoms were tiny spheres, that couldn’t be broken, specific to different elements.
What happened to the model nearly 100 years after 1804 ?
JJ Thompson discovered removable electrons, and suggested atoms were balls of positive charge with electrons stuck in them. The plum pudding model.
What happened to the model in 1909 ?
Scientists in Rutherford’s lab fired alpha particles at thin gold foil - alpha scattering experiment.
What happened in the alpha scattering experiment ?
They were expecting the majority of alpha particles to pass straight through, however a larger than expected portion were deflected at greater angles than expected.
What happened as a result of the alpha scattering experiment ?
They realised most of the mass of an atom was concentrated at the centre in a positive nucleus, and also that the atom was mostly empty space - the nuclear model.
What did Niels Bohr refine in the nuclear model ?
He theorised electrons orbited the nucleus at fixed distances (energy levels), which matched experimental data.
How was the nucleus adapted after the discovery of electron shells ?
The proton was discovered through further experimentation.
Who discovered the neutron ?
In 1932 James Chadwick proved the existence of neutrons - explaining the imbalance between the atomic and mass numbers.
What does today’s model of the atom look like ?
Nucleus 10000 times smaller than the radius of the atom, it contains protons and neutrons; the rest is mostly empty space with negative electrons orbiting in shells. Radius of an atom is around 1 × 10^-10m.
What does the number of protons determine ?
The element that an atoms is, all atoms of an element have the same number of protons - this is the atomic number.
What is the mass number of an atom ?
Signifies the relative mass of the nucleus, number of protons + number of neutrons.
What is an isotope ?
Atoms of an element with the same number of protons but a different number of neutrons.
How many isotopes do atoms have ?
All atoms have different isotopes but there are usually only one or two stable ones.
What happens to unstable isotopes ?
They decay into other elements by giving out radiation to become more stable - radioactive decay.
What is ionising radiation ?
Radiation that knocks electrons off atoms creating positive ions, ionising power relates to how easily radiation can do this.
What do radioactive substances release ?
Ionising radiation (alpha,beta,gamma), and also sometimes neutrons when they decay.
What is an alpha particle ?
Comprised of two neutrons and two protons (helium nucleus).
What are the characteristics of alpha particles ?
Low penetration depth (few cm in air and absorbed by sheet of paper), large size means they’re highly ionising.
What are beta particles ?
A high speed electron, no mass and a charge of -1. And for every beta particle emitted a neutron in the nucleus turns into a proton.
What are the characteristics of beta particles ?
Moderately ionising, and moderate penetration depth (few meters in air and stopped by sheet of aluminium - 5mm)
What are gamma rays ?
They are EM waves with short wave lengths released by the nucleus.
What are the characteristics of gamma rays ?
Long penetration depth (stopped by thick lead or meters of concrete), weakly ionising as they can pass through rather than collide with atoms.
What are nuclear equations ?
A way of showing radioactive decay, written in the form: atom before decay –> atom after decay + radiation
How are alpha particles written in nuclear equations ?
Can be written as a helium nucleus.
How does emitting an alpha particle affect the original atom ?
Its atomic number is reduced by 2, and the mass number reduced by 4.
How does an emitted beta particle affect the original atom ?
The mass of the nucleus doesn’t change (1 neutron lost, 1 proton gained) and atomic number increased by 1.
How does emitting a gamma ray affect the original atom ?
They don’t change anything, they’re a way of getting rid of excess energy from a nucleus.
How can radiation be measured ?
With a geiger-muller tube and counter, which records the count rate.
What is count rate ?
The number of radiation counts per second.
What is a half-life ?
The time it takes for the amount of radiation emitted by a source to halve or the number of radioactive nuclei in an isotope to halve.
What is activity ?
The rate at which a source decays, measured in becquerels, Bq (1 Bq is 1 decay per second)
What does having a short half-life mean ?
Activity falls quickly - unstable nuclei rapidly decay, this is dangerous because of the high amount of radiation emitted at the start.
What does having a long half-life mean ?
Activity falls more slowly - releasing small amounts of radiation over a long time.
What is background radiation ?
The low-level radiation around us all the time.
Where can background radiation come from ?
Naturally occurring unstable isotopes, radiation from space (cosmic rays) mostly from the sun, and due to human activity (i.e nuclear waste).
What is the radiation dose ?
Tells you the risk of harm to body tissues due to exposure to radiation. Measured in Sieverts (Sv)
What affects your radiation dose ?
Where you live, if your jobs involves radiation, and other factors such as x-rays.
What is irradiation ?
Exposure to radiation, objects near to a radioactive source are irradiated. Irradiating something doesn’t make it radioactive.
How can you reduce irradiation ?
Keeping sources in lead lined boxes, standing behind barriers or handling sources remotely.
What is contamination ?
Where radioactive particles get onto the object
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