3.1.1.2 Mass number and isotopes Flashcards
What is the Atomic Number?
- The number of protons in the nucleus
- Represented by Z
What is the Mass Number?
- The total number if protons and neutrons in the nucleus
- Represented by A
What is an Isotope?
Atoms with the same number of protons but a different number of neutrons
What does a Time of Flight Mass Spectrometer do?
It gives us information about the relative atomic mass of an element and the relative abundance of its isotope
What are the 4 main steps of a ToF mass spectrometer?
Ionisation
Acceleration
Ion Drift
Detection
What are the two types of isonisation?
Electrospray and Electron Gun
How does Electronspray work?
- High Mr Substance
- Dissolved in volatile solvent and forced in a thin hypodermic needle
- Needle is connected to a positive voltage
- Due to the positive side, the substance gains a H+ ion making them positively charged
- Solvent removed, leaving a gas made up of positive ions
What is the equation for electrospray ionisation?
X + H+ –> XH+
How does Electron Impact work?
- Low Mr substance
- Sample is then vapourised
- ‘Electron gun’ fires high energy electrons at it
- Thiss knocks one electron off each particle so that they become positvly charged
What is the equation for electron impact?
X –> X+ + e-
What happens during the acceleration phase?
- The postivie ions are accelerated in the electrical field
- The field gives each ion the same kinetic energy
What happens during the ion drift phase?
- Ions enter an area where no electircal current is present so travel at a constant speed
- Lighter ions travel faster as they weigh less
- Heavier ions travel slower as they weigh more
What happens during the detection phase?
- The ion then gets detected due to the fact that a current gets induced when the ion hits the detector
