Flashcards in Atomic Physics - Paper 1 Deck (62)
State the typical size of an atom
1 x 10 -10 m
Describe the structure of an atom
A positively charge nucleus containing protons and neutrons surrounded by negatively charged electrons
State the size of a nucleus compared to an atom
The radius of the nucleus is less than 1/10000 of the radius of an atom
How can electrons move to a higher energy shell/level
By absorbing electromagnetic radiation
How can electrons move to a lower energy shell/level
By releasing electromagnetic radiation
What is the charge on an atom why?
Atoms are neutral as the number of positive protons is equal to the number of negative electrons
What is an Ion?
A charged atom that has gained or lost electrons
The same element must always have the same number of...?
Define the atomic number
Number of protons = number of electrons for an atom
Define nucleon number
mass mummer = Number of protons + number of neutrons
Define an isotope
The same element with the same number of protons but with a different number of neutrons.
Describe how the model of the atom has changed with new experimental evidence
Atoms were originally though to be tiny spheres that couldn't be divided.
The discovery of the electron led to the plum pudding model of the atom.
The alpha particle scattering experiment led to the nuclear model of the atom - a positive nucleus which contained the majority of the mass.
Niels Bohr suggested that electrons orbited the nucleus in shells
James Chadwich discovered the neutron
Describe the plum pudding model of the atom
A positive sphere with negative electrons dotted throughout it.
Describe the alpha particle scattering experiment.
Alpha Particles were fired at thin gold in a vacuum.
Describe and explain the observations from the alpha particle experiment.
The majority of alpha particles went straight though the gold. so atoms are mainly empty space.
Some alpha particles were defected by the gold foil. there must be something positive which contained the majority of the mass in an atom (the nucleus)
A tiny fraction of alpha particles bounced back where they came from. the nucleus must be a tiny part of the atom
How can an unstable nucleus become more stable?
By giving out radiation (alpha, beta or gamma)
The rate at which a source of unstable nuclei decays
State the units of activity
Define count rate
The number of decays recorded by a detector (GM tube)
Describe a alpha particle
Two protons and two neutrons together. A helium nucleus
Describe a beta partice
A fast moving electron ejected from the nucleus. This happens after a neutron has decayed into a proton
Describe a gamma ray
An electromagnetic wave with no charge or mass.
State the penetrating power of alpha, beta and gamma radiation.
Penetrating power is what can stop the radiation.
Alpha - skin, paper 5 - 10 cm of air
Beta - mm's of aluminium, 1 meter of air
Gamma - reduced by cm's of lead or m's of concrete
State the ionising ability of alpha, beta and gamma radiation.
Ionising ability is the ability to do damage to our living cells and tissues.
Alpha - highly ionising
Beta - moderately ionising
Gamma - very weakly ionising
In decay equations what is the mass number and proton number for an alpha particle?
mass number = 4
proton number = 2
In decay equations what is the mass number and proton number for a beta particle?
mass number = 0
proton number = -1
In decay equations what is the mass number and proton number for a gamma wave?
mass number = 0
proton number = 0
how can the rate of radioactive decay be increased?
It can be affected by physics quantities such as temperature or pressure. it is completely random.
Define half life
The time taken for the number of radioactive nuclei in a sample to half.