Atomic Physics - Paper 1 Flashcards
To revise Atomic physics (paper 1)
State the typical size of an atom
1 x 10-10 m
Describe the structure of an atom
A positively charged nucleus containing protons and neutrons surrounded by negatively charged electrons in shells.
State the size of a typical nucleus?
1 x 10-15 m
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 energy in the form of electromagnetic radiation. This is called excitation.
How can electrons move to a lower energy shell/level
By releasing energy in the form of electromagnetic radiation. This is called relaxation.
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…?
Protons
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.
Neils 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)
Define activity
The rate at which a source of unstable nuclei decays
State the units of activity
Becquerel (Bq)
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.