The total number of protons and neutrons in the nucleus of an atom.
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Define 'isotope'
Atoms with the same atomic number but different mass numbers, ie. same number of protons, different number of neutrons.
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What happens to chemical properties in isotopes?
They remain the same as isotopes have the same number of electrons in their outer shell.
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What happens to physical properties in isotopes?
They are slightly different because isotopes have a different mass number.
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Define 'isotopic signature'
The percentage of each isotope to show how much of each different type there is.
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What will isotopes of an element with fewer neutrons have?
Lower masses, lower densities, a faster rate of diffusion, and lower melting and boiling points.
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What are radioactive isotopes?
Unstable isotopes, which decay by giving off radiation.
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What can radioactive isotopes be used for?
Tracers. Eg. Iodine-131 detects tumours.
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What two things is mass spectroscopy used for?
1) To measure the relative masses of isotopes. 2) To find the relative abundance of the isotopes in a sample of an element.
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What happens during ionisation in the mass spectrometer?
The gaseous sample is bombarded by a stream of high-energy electrons. These high-energy electrons can 'knock' an electron from an atom, producing a positive ion.
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What happens during acceleration in the mass spectrometer?
An electric field is used to accelerate the positive ions towards the magnetic field or electromagnet.
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What happens during deflection in the mass spectrometer?
Accelerated ions are deflected in the magnetic field.
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What happens during detection in the mass spectrometer?
A tiny current is produced when a positive ion reaches the detector. This signal is fed to a recorder which counts the number of signals for each setting of the magnetic field. All the counts together produce a mass spectrum.
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Define 'relative atomic mass'
The average mass of an atom, taking into account the abundances of all its isotopes, compared with 1/12 of the mass of one atom of Carbon-12.
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Define 'relative molecular mass'
The average mass of a molecule in relation to 1/12 of the mass of one molecule of Carbon-12.
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Define 'first ionisation energy'
The energy required to remove one electron from each of a mole of free gaseous atoms in that element.
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What is Hund's rule of maximum multiplicity?
Electrons organise themselves so that as far as possible they remain unpaired, occupying the maximum number of sub-level orbitals possible.
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What is the trend for first ionisation energies for group 2 elements?
There is a successive decrease. Mg is lower than Be because its outer electron is in a 3s sub-level (rather than a 2s) and so its outer electron can be more easily removed.
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What is the trend for first ionisation energies for period 3 elements?
There is a general increase - nuclear charge increases, so electrons are attracted more strongly to the nucleus and it takes more energy to remove one from the atom.
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Why is there a fall in first ionisation energy between Mg and Al?
Because the Al outer electron is in a p sub-level, which is higher in energy than the outer electron in Mg, which is in an s sub-level.
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Why is there a fall in first ionisation energy between P and S?
Because the 3p electrons in phosphorus are unpaired. In sulphur, one of the 3p electrons is paired, which causes some repulsion and therefore increases their energy, making them easier to remove.
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Why does the first ionisation energy of atoms generally increase across a period?
The number of electrons increases, however the shell size remains the same, so the nuclear charge increases and it is more difficult to remove the electrons - so the amount of energy required increases.
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Why do first ionisation energies decrease down a group?
Because the outermost electrons are increasingly shielded from the attraction of the nucleus, so they are easier to remove.
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Why does helium have the highest first ionisation energy of all the elements?
Because the sub-shell is completely filled and there is no shielding, so the electron is held closer than in other periods.
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Why is the second ionisation energy of an atom always greater than the first?
Because removing an electron from an ion requires more energy - there are fewer electrons, so outer electrons are more strongly held to the nucleus (so it takes more energy).
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How is the R.M.M of a covalent compound obtained from its mass spectrum?
Its Mr will be equal to the highest m/z value.
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Other cards in this set
Card 2
Front
Define 'mass number'
Back
The total number of protons and neutrons in the nucleus of an atom.
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