Atomic Structure Flashcards
What is the mass number of an element?
Protons + neutrons
What is the atomic number of an element
Number of protons
What are the relative charges for a proton neutron and electron?
Proton = +1
Neutron =0 neutral
Electron =-1
What is the structure of an atom?
Central nucleus with protons and neutrons surrounded by shells of orbiting electrons
What is an isotope?
An element with the same number of protons and electrons it different mass number as there are a different number of neutrons
What is mass spectrometry? And how does it generally work?
Form of molecular chemical analysis.
- Forms ions
- Ions are separated according to their mass/charge ratio
- Ions are detected
What are the uses of mass spectrometry?
Provide structural information
Identify unknown compounds
To determine the relative abundance of each isotope of an element
How would you do an isotopic mass and abundance calculation for chlorine?
Isotope 35 =75%
Isotope 37= 25%
Therefore
(35 x 75) + (37 x 25) / 100 gives the average mass number
=35.5
Why is a time of flight mass spectrometer in a vacuum?
Prevents ions colliding with air.
What are he steps in a time of flight mass spectrometer?
- Ionisation
- Acceleration
- Ion drift
- Detection
- Data analysis
What happens during ionisation in a ToF?
An electron gun fires high energy electrons at the sample causing an electron to be knocked off forming a positive ion
What happens during the acceleration stage in a ToF
The ions are attracted to a negatively charged plate
This causes the ions to accelerate towards the plate so all ions have the same kinetic energy.
Therefore the larger, heavier particles have a lower velocity.
What happens during the ion drift stage of a ToF?
The ions pass through a hole in the negatively charged plate forming a beam of ions. This then travels along a tube (flight tube).
What happens during he detection stage in a ToF?
When the ions arrive at the detector their flight times are recorded.
Positive ions pick up an electron causing a current to flow.
Since the ions have a different mass some with arrive at a different time and therefore have a different mass spec reading.
What happens during the data analysis stage of a ToF?
The detector passes a signal to a computer once the current is available.
This generates a mass spectrum for that particular ion which then can be collated forming the overall structure of the element/ compound.
