Atomic Structure Flashcards
What are the three sub-atomic particles and their properties?
- Proton: Found in the nucleus, relative mass = 1, relative charge = +1
- Neutron: Found in the nucleus, relative mass = 1, relative charge = 0
- Electron: Found in orbitals, relative mass = 1/1840, relative charge = -1
What is the atomic number (Z)?
The number of protons in the nucleus of an atom.
What is the mass number (A)?
The total number of protons and neutrons in an atom.
How do you calculate the number of neutrons in an atom?
Number of neutrons = Mass number (A) - Atomic number (Z)
What are isotopes?
Atoms with the same number of protons but different numbers of neutrons.
Why do isotopes have similar chemical properties?
Because they have the same electronic structure.
What are the four main steps in a time-of-flight (TOF) mass spectrometer?
- Ionisation
- Acceleration
- Ion drift (flight tube)
- Detection
What are the two types of ionisation in mass spectrometry?
Electron impact ionisation and Electrospray ionisation
Describe electron impact ionisation.
- A vaporised sample is injected at low pressure.
- High-energy electrons are fired at the sample from an electron gun.
- This knocks out an outer electron, forming positive ions.
When is electron impact ionisation used?
For elements and substances with low formula masses.
Why is electrospray ionisation used for larger organic molecules?
It occurs under softer conditions, preventing fragmentation.
Describe electrospray ionisation.
- The sample is dissolved in a volatile, polar solvent.
- It is injected through a fine needle with high voltage.
- The sample gains a proton (H⁺) to form MH⁺ ions.
What happens during the acceleration step in TOF mass spectrometry?
- Positive ions are accelerated by an electric field to a constant kinetic energy.
- Lighter ions travel faster than heavier ones.
What happens in the flight tube (ion drift area) of a mass spectrometer?
- Ions with smaller m/z values move faster.
- Heavier ions take longer to travel through the drift region.
How does the detector in a mass spectrometer work?
- Ions hit the detector and generate a small current.
- The current is proportional to the abundance of the isotope.
What is the equation for time of flight in a TOF mass spectrometer?
t = \frac{d}{v}
where
- t = time of flight
- d = length of flight tube
- v = velocity of the ion
What happens if a 2+ ion is formed in mass spectrometry?
The mass-to-charge ratio (m/z) is halved. Example: ( 24Mg^{2+} ) has an m/z of 12 instead of 24.
What is the mass of one ion of ( ^{59}Ni^+ ) in kg?
\frac{59}{6.022 \times 10^{23}} = 9.797 \times 10^{-26} \text{ kg}
How do you calculate the time of flight for ( ^{59}Ni^+ ) in a 0.8000 m flight tube?
t = 0.8000 \times \sqrt{\frac{9.797 \times 10^{-26}}{2 \times 1.000 \times 10^{-16}}}
√ 5 ∫
t = 1.771 \times 10^{-5} \text{ s}
What are the properties of a proton?
- Found in the nucleus
- Relative mass = 1
- Relative charge = +1
What are the properties of a neutron?
- Found in the nucleus
- Relative mass = 1
- Relative charge = 0
What are the properties of an electron?
- Found in orbitals
- Relative mass = 1/1840
- Relative charge = -1
What is the equation for time of flight in a TOF mass spectrometer?
t = d / V
where t = time of flight, d = length of flight tube, V = velocity of the ion
What happens if a 2+ ion is formed in mass spectrometry?
The mass-to-charge ratio (m/z) is halved.
Example: 24Mgt* has an m/z of 12 instead of 24.
What is the mass of one ion of Nit in kg?
9.797 x 10^-23 kg
The mass is calculated using 59/6.022 x 10^23.
