IB Chemistry - Topic 14

• The octet rule states that atoms like to have a full outer shell, which in the majority of cases is eight electrons.
• The predicted bond angle for Nitrite is 120 degrees (<120 degrees), but the actual bond angle is 115 degrees.
• Cyanide has an electron domain geometry of 2 and a molecular geometry of linear.
• The predicted bond angle for Hydrogencarbonate is 120 degrees, but the actual bond angle is 120 degrees.
• Hydronium has an electron domain geometry of 4 and a molecular geometry of trigonal pyrimidal.
• Hydrogencarbonate has an electron domain geometry of 3 and a molecular geometry of trigonal planar.
• Hypochlorite has an electron domain geometry of 4 and a molecular geometry of linear.
• Beryllium and boron both form compounds which are exceptions to the octet rule as they have less than eight electrons around them in their compounds.
• The predicted bond angle for Nitrate is 120 degrees, but the actual bond angle is 120 degrees.
• The predicted bond angle for Carbonate is 120 degrees, but the actual bond angle is 120 degrees.
• Nitrate has an electron domain geometry of 3 and a molecular geometry of trigonal planar.
• Ammonium has an electron domain geometry of 4 and a molecular geometry of tetrahedral.
• The predicted bond angle for Hypochlorite is None, but the actual bond angle is None.
• Boron Tri Fluoride has an electron domain geometry of 3 and a molecular geometry of trigonal planar.
• Nitrite has an electron domain geometry of 3 and a molecular geometry of bent (V-shaped).
• The predicted bond angle for Cyanide is None, but the actual bond angle is None.
• The predicted bond angle for Ammonium is 109.5 degrees, but the actual bond angle is 109.5 degrees.
• The predicted bond angle for Hydronium is 107 degrees, but the actual bond angle is 107 degrees.
• Beryllium Chloride has an electron domain geometry of 2 and a molecular geometry of linear.
• Carbonate has an electron domain geometry of 3 and a molecular geometry of trigonal planar.
• Conjugation occurs when a molecule has both double and single bonds.
• In the propagation step of the nitrogen oxides mechanism, ozone reacts with nitrogen oxides to form nitrogen dioxide and oxygen.
• The remaining p orbital is perpendicular to the hybrid orbitals and can form a pi bond with the neighbouring carbon due to sideways overlap between the p orbitals.
• These free radical oxygen atoms are very reactive and combine with more oxygen molecules to form ozone.
• The overall effect of the nitrogen oxides mechanism is that ozone reacts with oxygen to form two molecules of oxygen gas.
• Resonance and delocalisation occur in the sulfur dioxide molecule, where electrons are delocalised over the three atoms.
• Delocalisation occurs when electrons have some freedom of movement across a molecule as opposed to being localised between two atoms.
• Nitrogen oxides (released by aircraft at high altitude) can also catalyse the destruction of ozone molecules.
• These hybrid sp orbitals will form sigma bonds with other atoms and occupy positions 180 degrees apart to minimise repulsion.
• Ozone is destroyed by lower energy UV light which causes the ozone molecule to revert back to an oxygen molecule and an oxygen radical.
• Bond order can be used to give a measure of the amount of double bond character between atoms in a resonance hybrid.
• In the sulfur dioxide molecule, electrons are delocalised over the three atoms.
• An electron is promoted from the 2s orbital into the empty 3pz orbital.
• The radical may then react with another ozone molecule forming two oxygen molecules.
• In ethyne, each carbon of the triple bond is sp hybridized.
• The remaining two p orbitals perpendicular to the hybrid orbitals and can form two pi bonds with the neighbouring carbon due to sideways overlap between the p orbitals.
• Initiation in the nitrogen oxides mechanism involves nitrogen gas reacting with oxygen gas to form nitrogen oxides.
• Only one of the p orbitals mixes with the 2s orbital forming two new sp hybrid orbitals.
• Ozone is created when high energy UV light causes homolytic fission in oxygen molecules creating free radicals (contain an unpaired electron).
• The sum of the electrons in the Lewis structure will equal the sum of the valence electrons of all atoms present (group number).