Atomic Structure

• What is the mass and charge of a proton?

  1
• What is the mass and charge of a neutron?

  Mass = 1 Charge = 0
• What is the mass and charge of an electron?

  Mass = 1/2000 Charge = -1
• What is the mass number?

  Total number of protons and neutrons in nucleus of an atom.
• What is the atomic (proton) number?

  Number of protons in nucleus of an atom.
• What are isotopes of an element?

  Atoms with same number of protons but different number of neutrons.
• Why do isotopes have same chemical properties?

  Number and arrangement of electrons decides chemical properties. Isotopes have same configuration of electrons, so have same chemical properties.
• Why do isotopes have slightly different physical properties?

  Physical properties depend more on mass of atom. E.g, different densities and diffusion rates.
• What was Dalton's model of the atom?

  Atoms are solid spheres. Different spheres made up different elements.
• What was J.J Thomson's model of the atom?

  Atom must contain even smaller, negatively charged particles (electrons). Plum pudding model. Positively charged, 'pudding'.
• What was Rutherford's gold foil experiment?

  Fired alpha particles (positively charged) at very thin sheet of gold. Expected most of alpha particles to be deflected slightly by positive, 'pudding' that made up most of atom. Most alpha particles passed straight through the gold atoms and very small number deflected backwards.
• What was Rutherford's nuclear model of the atom?

  Tiny, positively charged nucleus at centre, surrounded by a, 'cloud' of negative electrons. Most of atom is empty space.
• What was Bohr's model of the atom?

  Electrons only exist in fixed orbits and not anywhere in between. Each shell has a fixed energy. When an electron moves between shells, electromagnetic radiation is emitted or absorbed. As energy of shells is fixed, radiation will have a fixed frequency. Later refined model to include sub-shells.
• What was the issue with Rutherford's model of the atom?

  Electrons in, 'cloud' around nucleus would quickly spiral down into nucleus, causing atom to collapse.
• What is the relative atomic mass (Ar)?

  Average mass of an atom of an element on a scale where an atom of carbon-12 is exactly 12.
• What is the relative isotopic mass?

  Mass of an atom of an isotope of an element on a scale where an atom of carbon-12 is exactly 12.
• What is the relative molecular mass (Mr)?

  Average mass of a molecule on a scale where an atom of carbon-12 is exactly 12.
• What is the relative formula mass?

  Average mass of a formula unit on a scale where an atom of carbon-12 is exactly 12. Used for compounds that are ionic or giant covalent.
• What are the 4 steps in time of flight mass spectrometry?

  Ionisation, acceleration, ion drift and detection.
• What is electron impact ionisation?

  Sample vaporised and electron gun used to fire high energy electrons at it. This knocks 1 electron off each particle, becoming 1+ ions.
• Why do particles need to be ionised in TOF spectrometry?

  So they can be accelerated by electric field and detected by ion detector.
• What is electrospray ionisation?

  Sample dissolved in solvent and pushed through a small nozzle at high pressure. High voltage applied to it, causing each particle to gain an H+ ion. Solvent then removed, leaving a gas made up of positive ions.
• What happens during acceleration?

  Positive ions accelerated by electric field- gives same kinetic energy to all ions. Lighter ions experience greater acceleration as they're lighter, so accelerate more.
• What happens during ion drift?

  Ions enter region with no electric field. Drift through it at same speed as they left electric field-lighter ions will be drifting at higher speeds.
• What happens during detection?

  As lighter ions travel through drift region at higher speeds, they reach detector in less time than heavier ions. Detector detects current created when ions hit it and records how long they took to pass through spectrometer. Data used to calculate mass/charge values needed to produce mass spectrum.
• What is a mass spectrometer?

  Machine used to analyse elements or compounds. Gives info about relative atomic mass of an element and relative abundance of its isotopes or relative molecular mass of a molecule. Can be used to identify unknown compounds.
• What is fragmentation?


  Molecular ion breaks up, producing smaller peaks.
• What is the first ionisation energy?

  Energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions. KJ mol-1
• What factors affect ionisation energy?

  Nuclear charge, distance from nucleus and shielding.
• What happens when transition metals become ions?

  They lose their 4s electrons before their 3d electrons.
• Why are copper and chromium exceptions to electronic configuration?

  They donate 1 4s electron to their 3d sub-shell to be more stable.
• What is the second ionisation energy?


  Energy needed to remove an electron from each ion in 1 mole of gaseous 1+ ions.
• Why does first ionisation energy drop at Al?

  Its outer electron is in a 3p orbital rather than 3s. 3p orbital has slightly higher energy than 3s, so electron is further from nucleus. 3p orbital has additional shielding by 3s electrons.
• Why does first ionisation energy drop at sulphur?

  Electron repulsion.
• Why do successive ionisation energies increase within each shell of an atom?

  Electrons being removed from an increasingly positive ion- less repulsion amongst remaining electrons, so they're held more strongly by nucleus.
• Which method is more likely to result in ion fragmentation?

  electron impact
• What happens at the detector?

  Detection plate is negatively charged. Positive ions gain electron here to produce current. Amount of current produced is proportional to abundance of species.