Atomic Structure Flashcards
(37 cards)
Describe the plum pudding model.
It was a sphere of positive charge, with small negative charges distributed evenly within it.
Who was the lead scientist?When was it discovered?
JJ Thompson in 1897.
Who discovered atoms and when?
John Dalton in the early 1800s.
Who discovered the nucleus, when and how?
Ernest Rutherford in 1911. Through the gold foil experiment with alpha particles.
Who discovered orbitals and when?
Neils Bohr in 1913.
Who discovered neutrons and when?
Jame Chadwick in 1932.
What is the relative mass of an electron?
1/1840.
What is the mass number?
It’s the sum of the protons and neutrons in an atom.
What is the atomic number?
It’s the number of protons in an atom.
Define relative atomic mass.
The average mass of an atom of an element, divided by 1/12 of the mean mass of a carbon 12 isotope.
Define isotope.
Atoms of the same element with the same number of protons but with a different number of neutrons.
They react chemically int he same way but they will have different physical properties.
What are hydrogen isotopes?
Deuterium = 1 proton 1 neutron
Tritium = 1 proton 2 neutrons
What is an ion?
An ion is formed when an atoms loses or gains electrons meaning it’s no longer neutral and will have a charge.
What is mass spectrometry?
It’s an analytical technique used to identify different isotopes and find the overall relative atomic mass of an element.
What is Time of Flight (TOF) Mass spectrometry?
This records the time taken for ions of each isotope to reach a detector. Using this, spectra can be produced showing each isotope present.
Explain what happen in stage 1 - Ionisation in electron impact.
The sample is vaporised and then high energy electrons are fired at it with an ‘electron gun’ which is a hot wire filament with a current
running through it. This knocks off one electron from each particle forming a 1+ ion.
Explain what happen in stage 1 - Ionisation in electrospray ionisation.
The sample is dissolved in a volatile solvent (eg water or methanol) and injected through a fine hypodermic needle to give a fine mist. The tip of the needle is attached to the
positive terminal of a high-voltage power supply. The particles are ionised by gaining a proton from the solvent producing XH+ ions.
When do you use electron impact and when do you use electrospray ionisation?
Electrospray ionisation is used for molecules with higher molecular masses including biological molecules (eg proteins).
Electron impact is used for elements and substances with low formula mass (that can be inorganic or organic molecules).
Which type of ionisation is less prone to fragmentation?
Electrospray is known as a ‘soft’ ionisation technique where fragmentation rarely takes place. In electron impact, the molecular ion often breaks down into smaller fragments some of which are also detected
in the mass spectrum.
Explain stage 2 Acceleration.
The positive ions are accelerated using an electric field so that they all have the same kinetic
energy.
What equation would be used to calculate the velocity of the ions?
KE = 𝟏/𝟐𝒎𝒗^𝟐
KE = kinetic energy of particle (J)
m = mass of the particle (kg)
𝑣 = velocity of the particle (m s–1)
What variable does the velocity depend on?
As the kinetic energy is the same for all particles, the velocity of the ions depend on their mass. Lighter particles have a faster velocity, and heavier particles have a slower
velocity
Explain stage 3 – Flight tube
The positive ions travel through a hole in the negatively charged plate into a tube and are deflected by a magnetic field. The time of flight of each particle through this flight tube depends on its velocity which in turn depends on its mass.
What equation would you use for TOF flight tube?
𝒕 =𝒅/𝒗
t = time of flight (s)
d = length of flight tube (m)
𝑣 = velocity of the particle (m s–1)
