1.1 Atomic Structure

• How do you calculate the actual mass of an atom/species?

  Add together the weight of total protons, neurons and electrons.
• What does the mass number reprosent?

  The number of protons and neutron.
• What does the atomic number represent?

  The number of protons.
• If a halogen is negatively charged, what do you replace the end of the name with? E.g. Chlorine -> Chlor___

  'ide' E.g. Chlorine -> Chloride
• Why is it impossible to distinguish between 20Ne^+ and 40Ca^2+ isotopes?

  When using a mass spectrometer 20Ne^+ will show 20 in the m/z ratio and 40Ca^2+ will also show 20 as 40/2 is 20.
• Why is removing the second electron harder than removing the first?

  Once one electron is removed, the force of attraction between the protons and the electrons is greater, so losing a second electron is harder.
• Why does the whole process of mass spectrometry occur in a vacuum?

  To prevent ions formed colliding with the air.
• What are the 2 methods of ionisation?

  Electron impact and electro spray ionisation.
• Describe the process of electron impact ionisation. [3]

  The sample is vaporised and high energy electrons are fired at the particle from an 'electron gun'. This knocks off one electron from each particle, forming a 1+ ion.

  X(g) --> X^+(g) + e-
• What kind of elements or substrates are used in electron impact?

  Ones that have low formula masses. This includes inorganic or organic molecules.
• Why can't high formula mass elements or substrates be used with electron impact? [2]

  The molecular ion often breaks down into smaller fragments. Some of which are also detected in the mass spectrum.
• Describe the process of electrospray ionisation.

  The sample is dissolved in a volatile solvent. It is then injected through a hypodermic needle attached to a positive terminal of a high voltage power supply. The particles are ionised by gaining a proton producing XH^+ ions.

  X(g) + H^+ --> XH^+ (g).

  This produces ions with a single positive charge and a mass of Mr + 1.
• What kind of substances are used in electrospray ionisation? And what rarely takes place during this process?

  Substances with high molecular mass, including many biological molecules such as proteins. This is known as a soft ionisation technique and fragmentation rarely takes place.
• Which process of ionisation occurs in the gaseous state?

  Electron impact ionisation.
• What is the advantage of using electrospray ionisation over electron impact when trying to find the molecular mass of a molecule.

  When using electron impact, the particle fragments, which is not useful when trying to determine the molecular mass of a particle, this does not occur in electrospray ionisation.
• What happens during the acceleration stage of mass spectrometry?

  The positive ions are accelerated by attraction to a negatively charge plate using an electric field.
• During the acceleration stage of mass spectrometry, do all ions have the same kinetic energy?

  Yes
• What is the equation for kinetic energy?

  KE (J) = ½ x m (kg) x v^2 (ms^-1)
• Given that all particles have the same kinetic energy, what does the velocity of the particle depend upon?

  The mass of the particle, the lighter the particle the higher its velocity
• What is the next stage after the negatively charged plate during mass spectrometry.

  The positive ion will travel through a hole in the negatively charged plates into a time of flight tube.
• What does the time flight of a particle depend upon during mass spectrometry?

  The time of flight of each particle through this flight tube depends on its velocity, which in turn depends on its mass.
• What is the expression given for the time of flight across the flight tube?

  t = d/v

  t = time of flight (s)

  d = length of flight tube (m)

  v = velocity of particle (ms^-1)
• What happens during the detection phase of mass spectrometry?

  The positive ions hit a negatively charged electric plate. The positive ions gain electrons from the plate.
• During the data analysis of mass spectrometry how is a mass spectrum produced?

  A computer uses the data measured from the plate to produce a mass spectrum
• During the data analysis stage of mass spectrometry, how can you tell what the molecular ion is when observing the mass spectrum data produced by electronic impact?

  The signal with the greatest m/z value is the molecular ion and its m/z value gives the relative molecular mass. There may be some other small peaks present around the molecular ion, which are due to molecular ions that contain different isotopes. Peaks present roughly ½ or ¼ of the molecular ion m/z are due to fragmentation.
• What is the calculation for relative atomic mass?

  Avg mass of an atom of an element / number of atoms
• What state does first ionisation energy always occur in?

  The gaseous state
• Define ionisation energy

  The energy required to remove one mole of electrons from one mole of atoms in the gaseous state. It's measured in kJmol^-1
• The ionisation energy decreases as you go down group 1, Why is this?

  This is due to increased shielding, as a new shell is added each time this causes the valance electron to be at a greater distance from the nucleus. Therefore the valance electron is less attracted and can be lost easier.
• Ionisation energy generally increases across a period, give three reasons why the valance electron would be harder to remove.

  Firstly, there's an increased nuclear charge due to the presence of more protons.

  Secondly, there's a smaller distance from the nucleus.

  Both of these cause the valance electron to be more attracted and harder to remove.
• How do ionisation energy values provide evidence for the existence of principle energy levels?

  Due to dips in certain elements which can be explained by energy levels which are further from protons and thus have a weaker force of attraction and so can be lost easier
• How does the variation in ionisation energy across a period provide evidence for the existence of sub-levels?

  Due to certain dips in the period, the only explanation for them is that they're sublevels because, if there are sublevels present then electrons can be lost from it easier.
• Why does the first electron need the least ammount of energy to be removed in successive ionisation energies?

  Because it's being removed from a neutral atom
• Why does the second electron being removed require more energy to be removed than the first?

  Because it's being removed from a +1 atom. Which has the same number of protons but less electrons so the force of attraction between the two will be greater.
• How is data recorded from the detection plate during mass spectrometry?

  When the positive ions gain electrons from the plate a movement of electrons is generated casing an electric current to be produced. The size of the current produced gives a measure of the number of ions hitting the plate.
• How is relative abundance determined in mass spectrometry?

  As ions hit the detector each ion gains an electron, generating a current. This current is proportional to abundance.
• When calculating the mass number of an ion never include decimals in your answer. Your answer must be a whole number.
• Place these stages into the order that they happen in a time of flight (TOF) mass spectrometer:

  Acceleration, Data-analysis, Ionisation, Ion-drift and Ion-detection.

  Ionisation, Acceleration, Ion-drift, Ion-detection and Data-analysis
• Which of these elements will have the largest jump between second and third ionisation energies? Why?

  Aluminium, Magnesium, Chlorine, and Phosphorus.

  Magnesium as it's in group 2. Due to this the first two electrons are being removed from the outer shell, however, the third electron will be being removed from a shell closer to the nucleus. Requiring more energy to remove the electron.
• When writing ionisation's always include state symbols, gaseous.