1.1 Atomic Structure (part 1) Flashcards
What subatomic particles are atoms made up of
Protons, neutrons and electrons
What is the charge, mass and location of a proton?
Charge: +1
Mass: 1
Location: nucleus
What is the charge, mass and location of a neutron?
Mass: 1
Charge: 0
Location: nucleus
What is the charge, mass and location of an electron?
Mass: 1/2000
Charge: -1
Location: shells
Atomic number definition
Number of protons in the nucleus of an atom
Mass number definition
Number of protons and neutrons in the nucleus of an atom
Isotope
Atoms of the same element with a different number of neutrons
Why do isotopes have the same chemical properties?
Same no of elections> same electron configuration> dictates chemical behaviour
What is formed when an atom loses electrons
Positively charged ion (cation)
What is formed what an atom gains electrons?
A negative ion (anion)
What is mass spectrometry used for?
Determining information about elements and compounds, it can be used to calculate relative atomic mass of an electrons or relative molecular mass of a compound
What are the four stages of mass spectrometry
- ionisation
- acceleration
- separation of ions
- detection
What two methods of ionisation are there
Electron impact and electrospray ionisation
What are the 3 stages of electron impact ionisation
- sample injected into spectrometer and vaporised
- high energy electrons from electron gun fired at sample
- high energy electrons knock off an electron from each particle to form positive ions
What would the equation be if gaseous sodium was ionised by electron impact ionisation
Na (g) -> Na+ + e-
What are the 4 stages of electrospray ionisation?
- sample dissolved in polar solvent
- injected through a fine hypodermic needle to give a fine mist
- tip of needle is attached to the positive terminal of a high voltage supply
- particles gain a proton (H+ ion) from the solvent to form positive ions
What would the equation by if methane was ionised by electrospray ionisation
CH4 + H+ -> CH5+
What is the mass of the ion after electron impact ionisation
Mass of ion= mass of element/compound
What would the mass of an ion be if it was ionised by electrospray ionisation?
Mass of ion = mass of element/compound +1
What happens in acceleration?
An electric field is applied to accelerate the positive ions. This gives all the ions with the same charge the same kinetic energy
Do lighter or heavier ions travel faster
Lighter
What happens in seperation?
Lighter ions reach the detector first
Heavier ions reach the detector last
Why is the spectrometer kept under a vacuum?
To prevent other molecules in air colliding with the sample ions
What does a detector do
Records the different ions as they arrive at the detector
Why can ions be detected
They gain an electron at the detector to produce a current. The more ions of one type, the greater the current and bigger the peak
How is mass spectra plotted
Relative abundance against mass to charge ratio
Why is there never a peak at the relative atomic mass of an isotopic element?
The relative atomic mass is an average
Why must the sample be ionised?
So it can be accelerated and detected
Isotopic mass
The mass of an isotope relative to 1/12th the mass of an atom of carbon 12
Relative atomic mass
Weighted average mass of all the isotopes relative to 1/12th the mass of a carbon-12 atom
How to calculate the relative atomic mass
(Massxabundance of each isotope)/total abundance
How to calculate the relative atomic mass from mass spectra
Multiple each m/z by relative abundance and add them up, divide the whole thing by 100
What is molecular ion peak of CH3OH (electron impact)
M/z = 32 (CH3OH+)
Why would there be a peak at 33 in methanol (electron impact)
Small amount of carbon 13 present
Why would there be peaks below 32 in methanol (electron impact)
Molecule fragments until electron impact
Which peak in mass spectra shows the complete molecule (electron impact ionisation)
The peak furthest to the right
How does mass spectra from electrospray ionisation differ from electron impact
Does not cause fragmentation of the molecular ion so fewer peaks are present
Why would there be a peak at m/z 265 C12H24O6 (electrospray)
Gains hydrogen ion
C12H25O6+
Why would there be a peak at m/z 266 in mass spectra for C12H24O6 (electrospray)
Carbon 13= C13H25O6
Why would there be no peaks below 265 in mass spectra of C12H24O6 (electrospray)
No fragmentation
Ion in electron impact
M+
Ion in electrospray ionisation
MH+
