Atomic Structure Flashcards
as chem
Summary of the steps in Time of Flight Mass spectrometer?
1) Vaporisation
2) Ionisation
3) Acceleration
4) Ion drift
5) Detection
What happens during vapourisation?
The sample is vaporised so it can travel through the TOF mass spectrometer.
What happens during ionisation?
(electron impact) and (electron spray)
Electron impact:
an electron gun fires high energy electrons at the sample
This knocks out an outer electron
Forming positive ion.
Ti(g)–> Ti+ (g) +e-
Electron spray:
The sample is pushed through a nozzle making a high pressure jet. A high voltage is passed through causing the loss of an electron.
The sample gains a proton (h+) from solvent forming MH+
M(g) + H+ –>MH+ (g)
What happens during acceleration?
The positive ions are passed through an electric field. Particles with lower mass/charge (m/z) ratio will accelerate quicker.
What happens during ion drift?
Particles travel through with a constant speed and kinetic energy. They drift through and particles with lower mass/charge (m/z) ratios travel faster.
What happens during detection?
lons are detected as electrical current is made when particle hits the plate.
Particles with lower m/z reach the detector first as they travel fastest.
Meaning of relative atomic mass?
The average mass of an atom of an element when measured on scale on which the mass of an atom of 12C is exactly 12.
Meaning of relative molecular mass
The average mass of a molecule when measured on scale on which the mass of an atom of 12C is exactly 12.
Meaning of relative isotopic mass
The mass of an atom of an isotope of an element measured on scale on which the mass of an atom of 12C is exactly 12.
What does m/z refer to on a mass spectra graph?
The mass of an isotope divided by charge.
(as most isotopes have a 1+ charge this often is the same as the isotopic mass)
What is always on the y axis of a mass spectra graph and how is it presented?
It can be presented as a percentage or nominal value.
If it is % percentage abundance then all isotopes must add to give 100%.
How to work out relative atomic mass?
Total abundance
What do peaks show in mass spectra’s?
Fragments of the original molecule.
What does the last peak show ?
It’s referred to as the m+1 peak / molecular ion peak.
This is the same as the relative molecular mass of the molecule
What are the 4 sub shells and how many electrons can fit into each one?
S - (1 orbital) 2 electrons
P - (3 orbitals) 6 electrons
D - (5 orbitals) 10 electrons
F - (7 orbitals) 14 electrons
Why are orbitals filled up singly and then paired?
Due to electron repulsion
How do chromium and copper behave differently?
- An electron from 4s orbital moves into 3d orbital to create a more stable half full pr full 3d sub-shell.
cr–> 3d5, 4s1
cu–>3d10- 4s1
Ionisation energy meaning?
Ionisation energy is the minimum amount of energy required to remove 1 mole of electrons from 1 mole of atoms in the gaseous state.
What is the effect of shielding on ionisation energy?
The more electron shells between positive nucleus and negative (outermost) electron that is being removed the less energy is required. There is a weaker attraction.
What is the effect of nuclear charge on ionisation energy?
The more protons in the nucleus the bigger the attraction between nucleus and outer electrons. This means more energy required to remove the electron. (number of protons increase along period)
What is the effect of atomic size on ionisation energy?
The bigger the atom the further away the outer electrons are from the nucleus. The attractive force between nucleus and outer electrons reduces - easier to remove electrons.
Why does successive ionisation change?
As more energy is required to remove electron from sub shell closer to the nucleus of an atom due to stronger attraction.
How does ionisation energy change going down a group?
IE decreases down groups as atomic size increases so the attractive force between nucleus and outermost electron is weaker.
Shielding also increases going down groups this also makes the attractive force weaker.
How does ionisation energy vary going across a period?
It generally increases due to increasing number of protons in the nucleus which increases nuclear attraction but shielding stays the same.
What are the exceptions going across period 3?
- decrease at aluminium ( the outer electron in aluminium sits in a higher sub-shell 3p1 compared to mg 3s2 so slightly easier to remove electron)
- decrease at sulfur (evidence for electron repulsion as sulfur has 2 electrons in one orbital its easier to remove due to electron repulsion)
