atomic structure PMT Flashcards
Q11d Give two reasons why it is necessary to ionise the isotopes of chromium before they can be analysed in a TOF mass spectrometer.
ions will interact with and be accelerated by electric field
ions create a current when hitting the detector
Q13a Describe how the molecules are ionised using electrospray ionisation.
sample is dissolved in a volatile solvent
injected through needle at high voltage
each molecule gains a proton
Q14 The first ionisation energies of the elements in Period 2 change as the atomic number increases.
Explain the pattern in the first ionisation energies of the elements from lithium to neon.
first ionisation energy increases because proton number/nuclear charge increases. sheilding is similar so there is stronger attraction between nucleus and outer electron
deviation Be -> B
B is lower than Be as outer electron in Be is in 2P which is higher than 2S (B)
deviation N -> O
O is lower than N as there is 2 electron in 2P as a pair, pair causes electron repulsion
Q26e State and explain the trend in the first ionisation energies of the elements in Group 2 from magnesium to barium.
decrease
ions get bigger so more energy shells
weaker attraction of ion to lost electron
Q27b Describe how ions are formed in a time of flight (TOF) mass spectrometer.
the sample is bombarded by high energy electrons
the sample molecule loses an electron forming M+
Q27c A TOF mass spectrometer can be used to determine the relative molecular mass of molecular substances.
Explain why it is necessary to ionise molecules when measuring their mass in a TOF mass spectrometer.
Ions, not molecules, will interact with and be accelerated by an electric field
Only ions will create a current when hitting the detector
Q28b Outline how the TOF mass spectrometer is able to separate these two species to give two peaks.
Positive ions are accelerated by an electric field To a constant kinetic energy
The positive ions with m / z of 104 have the same kinetic energy as those with m / z of 118 and move faster
Therefore, ions with m / z of 104 arrive at the detector first
