1.1 Atomic Structure Flashcards
Relative charge and mass of a proton?
Charge: +1
Mass: 1
Relative charge and mass of an electron?
Charge: -1
Mass: 1/1840
Relative charge and mass of a neutron?
Charge: 0
Mass: 1
If an element is described as an atom what is significant?
It has the same amount of electrons as the protons
Why are there decimals numbers for some of the atomic mass numbers?
There are can be many isotopes of an element therefore an average is taken to acquire the number
What are the properties of an isotope?
Same number of protons and electrons
Different number of neutrons
Identical chemical properties because of the same electron configuration
How do you identify an element?
Using the atomic number/proton number
What is mass spectrometry?
It can identify relative isotopic mass
The relative abundance of isotopes
It can be used to identify elements
It can be used to determine relative molecular mass
What kind of mass spectrometer do we learn about?
Time of Flight
TOF
What must be present within the mass spectrometer?
Kept under vacuum to reduce the possibility of intermolecular collisions
E.g between the sample and the air
This is because it would interfere with the accuracy of the process
What are the stages of mass spectrometry?
Vaporisation Ionisation Acceleration Ion Drift Detection Data Analysis
What happens in vaporisation?
The sample has to be turned into a gas if it isn’t already
What does ionisation do to the sample in mass spectrometry?
Mass spectrometry can only work if the particles are charged and usually positive ions are generated
This is so you can control the particles much easier
What are the types of Ionisation?
Electron Impact
Electrospray
How does electron impact work?
It is the traditional method for producing ions in MS
It involves bombardment of the sample with a high energy beam of electrons
When the electrons hit the sample they sometimes remove another electron
The electrons fired are not absorbed
M + e- ——> M+ + 2e-
What can happen with electron impact?
It can often result in fragmentation
How does ionisation by Electrospray work?
Sample is dissolved in a volatile solvent
Forced into a fine hollow needle
This is connected to the positive terminal of a high voltage supply
The mixture is sprayed as a fine mist of droplets with the solvent evaporated
The sample picks up a proton (H+ ion) or sometimes ammonium salts are used
M + H+ ——> MH+
Which of the two ionisation techniques are better for larger molecules? Why?
Electrospray
It is considered a ‘soft’ ionisation technique as it is less likely to fragment the sample
What happens during acceleration?
The positive ions are attracted towards a negatively charged plate
The speed they reach is dependent on their mass to charge ratio
They are forced into a thin beam
What happens in ion drift?
They ions are separated according to how fast they travel through a ‘drift chamber’
They have different velocities because of their different masses
The ions are accelerated with the same kinetic energy because of the electric field they are in
Atoms with a lower mass have a higher velocity so arrive at the detector before those with a higher mass
What is the equation for kinetic energy?
KE = 1/2 mv^2
What happens at detection?
Ions hit a negatively charged plate and a current is generated when an electron is accepted and the positive ion is discharged
The time of flight of the ion is recorded
In detection what is the size of the current related to?
The number of ions hitting the detector
What is acquired in data analysis?
The mass to charge ratio of the ions and their relative abundance
How do you calculate RAM from mass spectrometry?
(Mass to charge ratio x relative abundance) + (repeat for as many)
Divided by total number of ions
What is the highest peak on a mass spectrum in Electrospray ionisation? What do you have to remember?
Protonated molecular ion peak
You have to take one away as a hydrogen was absorbed in the ionisation
What is the benefit of low resolution spectrometry?
It is cheaper
What is the benefit of high resolution spectrometry?
You can see more detail and distinguish between substances with a similar RAM
