Atomic Structure Flashcards
Electrospray Ionisation
Sample is dissolved in a volatile polar solvent
Injected through a needle at high voltage
each particle gains H+ proton to form 1+ ions
X(g)+H+->XH+(g)
Which elements deviate from full electron configuration
Cruc
Cu- 4s1 3d10
Cr-4s1 3d5
Ionisation energy down the groups
Decreases down the groups as the electron is removed from a higher principal energy level which is further from the nucleus so there is more electron shielding so less energy is required
electron impact ionisation
High energy electrons are fired from an electron gun.
These knock an electron off each particle to form 1+ ions
X(g)->X+ + e-
Velocity
D/T
Ionisation energy from group 5- group 6
goes from 3p3 to 3p4
ionisation energy decreases as 2 electrons share a p orbital
extra repulsion means less energy is required to remove the electron
Ionisation energy across the periods
Ionisation energy increases as the number of protons increases
shielding is constant
more energy is required to remove the electron
Ionisation energy from group 2 - group 3
2s2 -> 3p1
Ionisation energy decreases as electron is removes from the higher energy p sub-shell
less energy is required
How to find mass from kinetic energy
2KE/v^2
Equation when you are given time of flight for 1 ion and told to find it for the next
m1/(t1)^2 = m2/(t2)^2
Why is the second ionisation energy higher than the first?
The electron is being removed from a positive ion so more energy is required
the electron being removed is closer to the nucleus
Do heavier or lighter isotopes travel faster in a time of flight where they have constant kinetic energy
heavier isotopes have a lower velocity so they travel slower
how many decimal points for mass number?
0
mass numbers are whole numbers
define relative atomic mass
average/mean mass of 1 atom of an element compared to 1/12 mass of one carbon 12 atom.
Why are successive ionisation energies increase always
-positive charge increases
-ionic radius decreases
-shielding is constant
-nuclear attraction on electron increases
Mass spectra for chlorine ions, 2 isotopes 3:1
35-35 most common
37-37 least common
9:6:1
Mass spectra for Br2
2 isotopes
79-81 is most common as it is both 79-81 and 81-79
1:2:1
Mass spectra and electron impact ionisation
covalent bonds can be broken into fragments
this happens to just some molecules so some just gain a positive charge
these give peak m/z with the highest value
small peak above this is from isotopes of hydrogen and carbon
Data analyses in time of flight
-detector linked to an amplifier then to a recorder which converts the current into a peak and shown then in a mass spectrum
-height of the peak is proportional to the size of the current so is proportional to abundance
m/z mass/charge ratio is usually the same as the mass number
if it gains a proton its one higher
detection in time of flight
-positive ions hit detector and pick up an electron
-this causes a current to flow
-greater the abundance the bigger the current
current directly proportional to the abundance
acceleration in time of flight
positive ions are accelerated by an electric field to a constant kinetic energy
ion drift in time of flight
-ions separate
-drift in flight tube of known distance
-time to reach detector is measured
-lower mass less time to reach detector
