Physical 1 Section 1 - Unit 1: Atomic Structure
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Explain why sulphur has a lower ionisation energy than phosphorus (2 marks)
• Sulphur’s outer 3p orbital is full so there is repulsion between the electrons • Meaning that less energy is needed to remove one of these paired electrons
State any differences and similarities (if any) in the atomic structure and chemistry of the isotopes of an element. (4 marks)
• Different number of neutrons • Same atomic number • Same chemical properties • Because same electron configuration
Explain why magnesium has a higher melting point than sodium (2 marks)
• Magnesium has more protons - So it attracts the delocalised electrons more strongly
Explain why metals are malleable (2 marks)
• The attractive forces are the same throughout the metal lattice • So the ions in the lattice can slide over each other
Explain why S8 has a higher melting point than P4 (2 marks)
• Sulphur has a greater Mr - So there are stronger Van der Waals forces
Explain why the boiling points of Hydrogen Halides increases down a group (2 marks)
• The size of the Van der Waals forces - Increases with the increasing size of the electron cloud
State whether aluminium or magnesium has a lower ionisation energy and explain why (3 marks)
• Aluminium • Because the outer electron is in a higher 3p subshell • Which is higher in energy and further away from the nucleus meaning that less energy is needed to remove the electron
Explain why the melting point decreases down group 2 (2 marks)
• Atomic radius increases down a group - So there is weaker metallic bonding (due to the weaker force on delocalised electrons)
Explain what is meant by the term relative isotopic abundance (2 marks)
• Ratio abundance of each isotope - Present in a sample of the element
Explain why silicon has a high melting point (3 marks)
• Silicon is macromolecular • Meaning that the covalent bonds need to be broken • And these bonds are very strong and require a lot of energy to be broken
Describe what change occurs to the motion of the ions in sodium chloride when it is heated from room temperature to a temperature below its melting point (1 mark)
• The ions vibrate faster
Explain why O-H is polar (2 marks)
• Oxygen is more electronegative than hydrogen - And this causes a higher electron density around oxygen atom
Explain why it is necessary to ionise molecules when measuring their mass in a TOF mass spectrometer (2 marks)
• Only ions will be accelerated by an electric field - Only ions will create a current when hitting the detector
Describe how ions are formed by electrospray in a TOF mass spectrometer (2 marks)
• Sample is dissolved in a polar solvent and passed through a positive terminal with a high voltage • Molecules gain a proton
Explain what accelerates the ions before they are deflected in mass spectrometry (1 mark)
• Electric field
Explain what deflects the moving ions round a curved path in mass spectrometry (1 mark)
• Magnet
State what is adjusted in a mass spectrometer in order to direct ions with different m/z values onto the detector (2 marks)
• Electric/ magnetic field - So that the deflection of ions onto the detector generates an electric current
Explain how ions are detected and relative abundance is measured in a TOF mass spectrometer (2 marks)
• Ion hits the negative plate and gains an electron - And relative abundance is proportional to the size of the current produced
Explain the increase in melting point from sodium oxide to magnesium oxide (2 marks)
• Greater charge density on magnesium ion - So there’s stronger ionic bonding
Explain why the melting point of the oxide of silicon is much higher than that of the highest oxide of phosphorus (3 marks)
• SiO2 is macromolecular • P4O10 is simple molecular • Covalent bonds of SiO2 are much stronger than the intermolecular forces in P4O10
Explain why silicon dioxide has a higher melting point than sulphur trioxide (4 marks)
• Covalent bonds in SiO2 • Van der Waals forces in SO3 • Covalent bonds are stronger than van der Waals forces • And so they require more energy to be overcome/broken
Explain the process of a mass spectrometer (6 marks)
• The sample is dissolved in a volatile, polar solvent • And passed through a positive terminal with a high voltage • This causes the sample to gain a proton and become positively charged • Positive ions are accelerated by an electric field • To a constant kinetic energy • The positive ions with smaller m/z values will have the same kinetic energy as those with larger m/z and will move faster • The ions hit the negative plate and gain an electron • And relative abundance is proportional to the size of the current produced
Define the term relative atomic mass (2 marks)
• Average mass of one atom compared to one twelfth of the mass of one atom of carbon-12
In a mass spectrometer, the relative abundance of each isotope is proportional to the current generated by that isotope at the detector. Explain how this current is generated (1 mark)
• Electrons transferred - From the detector to the positive ion