1.01 Atomic Structure

• Define relative atomic mass.

  Average mass of all isotopes of an element relative to 1/12 the mass of an atom of Carbon-12
• What are isotopes of an element?

  Different forms of the same element, containing the same number of protons but different numbers of neutrons. They still have the same chemical properties
• How many orbitals and electrons do these shells have?

  1s - 1 orbital, 2 electrons

  2p - 3 orbitals, 6 electrons

  3s - 1 orbital, 2 electrons

  3d - 5 orbitals, 10 electrons

  4s - 1 orbital, 2 electrons
• Does 3d or 4s have a higher energy?

  3d
• What is an orbital?

  A region around the nucleus that can hold up to 2 electrons.
• What would be the relationship between 2 electrons in the same orbital in terms of their spin?

  Have opposite spin as they repel eachother due to both being negative
• Explain why chromium does not fit the trend for electronic configuration

  It only has one electron in its 4s orbital before filling 3d

  1s2... 3p6, 4s1, 3d5
• Explain why copper does not fit the trend for electronic configuration

  It only has one electron in its 4s orbital before filling in 3d

  1s2... 3p6, 4s1, 3d10
• What is a type of ionisation for a mass spectrometer? (electron impact)

  1. Electron impact: electron gun (hot wire filament with current through it emitting electrons) knocks off one electron from each particle to form 1+ molecular ions (ions end up fragmenting)
• What is a type of ionisation for a mass spectrometer? (electrospray)

  • Electrospray: sample dissolved in a volatile solvent e.g water, and injected through a fine hypodermic needle to give it an aerosol. Needle attached to positive terminal of a high voltage power supply and particles gain a proton from the solvent as they leave the needle, producing XH+ ions (ions rarely fragment)
• When would you use the different types of ionisation in a mass spectrometer?

  Electron impact is used for organic/inorganic molecules with a lower formula mass

  Electrospray is used for substances with a higher molecular mass including biological molecules e.g proteins
• Describe how a time of flight mass spectrometer works


  Acceleration - positive ions attracted towards a negatively charged plate

  Ion drift - ions pass through a hole in the plate, form a beam with constant kinetic energy and travel along the tube to the detector. Time of flight is therefore d.p to the square root of mass

  Detection - positive ions pick up electrons, current flows, m/z value and time of flight recorded. Largest current generated by most abundant ions
• Define first ionisation energy


  The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+
• How does the distance from the nucleus affect ionisation energy?


  Attraction falls rapidly with distance. An electron close to the nucleus will be much more strongly attracted rather than an electron that is further away.
• How does nuclear charge affect ionisation energy?

  The more protons there are in a nucleus, the more positively charged the nucleus is, and the more strongly the electrons are attracted to it, as protons pull electrons inwards
• How does shielding affect ionisation energy?


  Electrons within inner orbits shield outer electrons from the electrostatic pull of the nucleus, reducing its effect. Therefore it is easier to knock out e-. The higher amount of e- in inner shells in relation to outer = more shielding
• What is the trend in ionisation energy across a period?


  Increases due to a decrease in atomic radius and stronger electrostatic forces between nucleus and electrons
• What is the trend in ionisation energy down a group?


  Ionisation energy decreases due to an increasing atomic radius and shielding which reduces effect of electrostatic forces between nucleus and electrons
• Why is there a decrease in ionisation energy between Mg to Al?

  The outer electron in aluminium is in a higher level (3p compared to 3s), so less energy is needed to remove it.
• Why is there a decrease in ionisation energy between P to S?


  In phosphorus, all the outer shell electrons are unpaired. In moving into sulfur, the next electron goes into a half filled orbital and the extra repulsion makes it easier to remove (1s2 2s2 2p6 3s2 3p3 [half full orbital] into 3p4 [1 full orbital and 2 half full orbitals])
• how do you calculate the mass of one atom/ion using avogadro's constant?

  molar mass/avogadro's constant