ATOMIC STRUCTURE

• What are the three sub-atomic particles of an atom?

  Protons, neutrons, electrons
• Protons are located in the nucleus
• Protons have a relative mass of 1 and a relative charge of +1
• Where are neutrons located in an atom?

  Nucleus
• Neutrons have a relative mass of 1 and a relative charge of 0
• Electrons are located in orbitals and have a relative charge of -1
• What is the relative mass of an electron?

  1/1840
• The atomic number (Z) represents the number of protons
• What does the mass number (A) represent in an atom?

  Protons and neutrons
• The number of neutrons in an atom can be calculated as A - Z
• Isotopes are atoms with the same number of protons but different numbers of neutrons
• Why do isotopes have similar chemical properties?

  Same electronic structure
• Isotopes may have slightly different physical properties due to their varying masses
• Arrange the essential steps of a time of flight mass spectrometer in the correct order.

  1️⃣ Ionisation

  2️⃣ Acceleration

  3️⃣ Flight tube

  4️⃣ Detection
• Two methods of ionisation in a mass spectrometer are electron impact and electrospray ionisation
• In electron impact ionisation, a vaporised sample is injected at low pressure
• What type of solvent is used in electrospray ionisation?

  Volatile, polar
• In electrospray ionisation, a sample molecule gains a proton (H+) from the solvent to form MH+
• The MH+ ions in electrospray ionisation move towards a negatively charged plate
• The mass spectrometer must be under a vacuum
• What type of molecules is electron impact ionisation best suited for?

  Low formula mass
• Electrospray ionisation is preferred for larger organic molecules because it avoids fragmentation
• Positive ions in a mass spectrometer are accelerated by an electric field
• What distinguishes ions in the flight tube of a mass spectrometer?

  Different flight times
• The size of the current generated in the detector is proportional to the abundance of the species
• The relative atomic mass (R.A.M) is a weighted average of all the isotopes
• Calculate the relative atomic mass of tellurium using the following data: 124-Te relative abundance 2; 126-Te relative abundance 4; 128-Te relative abundance 7; 130-Te relative abundance 6.

  127.8
• Mass spectrometers have been used in planetary space probes to identify elements with different isotopic compositions
• The peak in a mass spectrum with the largest m/z is called the parent ion or molecular ion
• What must be subtracted from the MH+ peak to find the Mr of a molecule in electrospray ionisation?

  1
• The 160 peak in the mass spectrum of bromine isotopes has double the abundance because there are two possible combinations
• The Bohr model of the atom places electrons in spherical orbits
• Which principal energy level is closest to the nucleus?

  1
• The s sub-level can hold up to 2 electrons
• Orbitals are regions of space that hold up to 2 electrons with opposite spin
• Which sub-levels are present in the second principal energy level?

  2s, 2p
• Arrange the sub-levels in order of increasing energy.

  1️⃣ 1s

  2️⃣ 2s

  3️⃣ 2p

  4️⃣ 3s

  5️⃣ 3p

  6️⃣ 4s

  7️⃣ 3d
• Spin diagrams use arrows to represent electrons, with opposite directions indicating different spins
• The s sub-level has a spherical shape
• What is the rule for filling sub-levels with multiple orbitals?

  Fill each singly first