Atomic Structure Flashcards
describe how molecules are ionised in electrospray ionisation:
- sample dissolved in highly volatile substance
- sample injected into hypo needle at a high voltage
- sample is vaporised and molecules gain H+ ions, forming 1+ ion
chemical properties are determined by
(number of) outer electrons
ions are accelerated by
attraction to an electromagnetic field
outline how TOF mass spec is able to seperate two species m/z 104 and m/z 118 to give 2 peaks
- +ve ions accelerated by electric field
- to a constant kinetic energy
- +ve ions w/ m/z 104 have same kinetic energy as the 108 m/z and move faster
- ions with m/z of 104 arrive at detector first
state if Al or Mg have lower first ionisation energy
- Al
- outer electron in 3p subshell
- further from nucleus so easier to remove
first ionization energy
energy needed to remove one mole of electrons from one mole of atoms (in gaseous state) to form one mole of monopositive ions (also in gaseous state)
Why does FIE generally increase across a period? (4)
- nuclear charge increases
- atomic radius decreases
- attraction betw/ nucleus and outer electrons increase
- more energy required to remove outer electron
chemical properties depends on
electronic configuration
define relative atomic mass
explain how RAM of an element w/ 3 isotopes can be calculated from data obtained from mass spectrum of the element
- average mass of an atom relative to mass of one atom of 12C
- spectrum gives relative abundance
- and mass number
- multiply mass number by relative abundance
- sum these values
- divide by the sum of relative abundances
name the shape, and bond angle, and explain, for AlCl4 -
- tetrahedral
- bond angle 109.5
- equal repulsion betw/ 4 bonding pairs
Explain why perfume is volatile and cools the skin when it evaporates (4)
- solvent has weak intermolecular forces betw/ molecules
- solvent needs energy to evaporate
- takes energy from skin, cooling it
- perfume slowly spreads by diffusion
name strongest type of bonding betw/ HF and why HI doesn’t contain this bonding
- hydrogen bonding
- (diagram w/ partial charges and 3 lone pairs on F)
- dipoles result from large difference in electronegativity
- difference in electronegativity betw/ I and H is too little
- HI dipole weaker
atomic radius gets:
- smaller across period
- larger down group
describe time of flight: electron impact
1. inject
2. ionise
3. accelerate
4. drift
5. detect
- inject liquid sample into machine
-sample gets vaporised into gas - sample gets bombarded by high energy e-, e- gets knocked off from sample turning it +ve
- +ve ions attracted to -vely charged plate
- sample enters flight tube, all ions have same KE
- lower Mr ions detected first
- ion gains e-
- relative abundance is proportional to the size of the current
describe time of flight: electron spray
- sample dissolved in highly volatile solvent
- sample injected out as aerosol, at a high voltage
- sample gains a proton becoming 1+ ion
write an equation for detection of M: electron impact, electrospray ionisation
- M+(g) + e- ➜ M(g)
- MH+(g) + e- ➜MH(g)
what are the limitations to electron impact?
high energy e- can cause fragmentation
what could cause different peaks to be shown on mass spectrum:
fragments
method to ionise sample in electrospray
- sample dissolved in volatile substance
- injected through hypodermic needle coming out as aerosol
- tip of needle has high voltage
- sample gains a proton as it leaves needle
method to ionise using electron impact
- vaporise sample
- sample gets bombarded by high energy electrons
- from electron gun
- knocks off e-
Why do samples need to be positively charged in a mass spectrometer?
so they can be ACCELERATED and DETECTED.
Also so an m/z exists, because without charge, there cannot be an m/z ratio, so the different masses cannot be differentiated in the ion drift.
When is relative molecular mass used instead of relative fomula mass?
RFM is used for compounds that are ionic or giant covalent
Chromium and copper have the following electron configurations:
Cr is [Ar] 3d5 4s1 not [Ar] 3d4 4s2
Cu is [Ar] 3d10 4s1 not [Ar] 3d9 4s2
This is because the [Ar] 3d5 4s1 and [Ar] 3d10 4s1 configurations are energetically stable
The Ionisation Energy (IE) of an element
the amount of energy required to remove one mole of electrons from one mole of gaseous atoms of an element to form one mole of gaseous ions
