3 - periodic table and energy

• activation energy is the minimum energy required for a reaction to occur
• properties of graphite

  1. planar arrangement of C atoms in layers so malleable so they can slide over each other
  2. delocalised electrons between layers so good conductor as they can move throughout the structure
• the boiling points of the halogens increase down the group as

  1. the number of electrons increase
  2. the size of the molecule increases
  3. size of induced dipole-dipole interactions between the molecules increase
• heterogeneous catalysts are in a different phase to the reactants and products
• homogeneous catalysts are in the same phase as the reactants and products, so they are not affected by the reaction
• le chatelier's principle states when a system in dynamic equilibrium is subject to change, the position of equilibrium will move to minimise the effects of the change
• melting points down group 2 decrease as

  1. metallic bonding weakens as atomic size increases
  2. distance between the nucleus and outer electrons increases
  3. electrostatic attractive forces between positive ions and delocalised electrons weaken
• metallic bonding is the electrostatic force of attraction btween positive metal ions and a sea of delocalised electrons
• periodicity is a repeating pattern across different periods
• pressure on equilibrium

  1. increase - equilibrium will move to the side with fewer moles of gas by reducing the pressure
  2. decrease - equilibrium will move to the side with more moles of gas by increasing the pressure
• helium has the largest first ionisation energy because

  1. it's first electron is in the first shell closest to the nucleus
  2. it has no shielding effects from inner shells
  3. bigger first IE than H as it has one more proton
• ionisation energies decrease down a group because

  1. outer electrons are found in shells further from the nucleus
  2. more shielded so attraction of nucleus becomes smaller
• ionisation generally increases across a period because

  1. electrons are being added to the same shell which has the same distance from the nucleus and same shielding effect
  2. the number of protons increase, making effective attraction of the nucleus greater
• Na has a lower first IE than Ne because

  1. Na will have it's outer electron in a 3s subshell further from the nucleus and is more shielded
  2. Na's outer electron is easier to remove and has lower IE
• there is a small drop in IE from Mg to Al because

  1. Al is starting to fill a 3p subshell whereas Mg has it's outer electrons in the 3s subshell
  2. electrons in the 3p subshell are easier to remove because they are higher in energy
  3. also slightly shielded by 3s electrons
• there is a small drop in IE from P to S because

  1. S has 4 electrons in the 3p orbital and its 4th is starting to doubly fill the first 3p orbital
  2. when the second electron is added to 3p orbital there is a slight repulsion between the two negatively charged electrons which makes the second electron easier to remove
• standard enthalpy of combustion is the enthalpy change when 1 mole of a substance is burnt in excess oxygen under standard conditions with all species in their standard states
• standard enthalpy of formation is the enthalpy change when 1 mole of a substance is formed from its constituent elements under standard conditions with all species in their standard states
• standard enthalpy of neutralisation is the enthalpy change when an acid and base react to form 1 mole of water under standard conditions with all species in their standard states
• standard enthalpy of reaction is the enthalpy change that accompanies a reaction in the molar quantities shown in the chemical equation
• temperature on equilibium

  1. increase - moves in endothermic direction and tries to reduce temperature by absorbing heat
  2. decrease - moves in exothermic direction to try and increase the demperature by giving out heat
• factors making a reaction less exothermic include

  1. heat released to the surroundings
  2. incomplete combustion
  3. non-standard conditions
• factors affecting ionisation energy

  1. nuclear attraction - more protons = greater attraction to electrons
  2. atomic radius - bigger atom = greater distance of nucleus and outer electrons = weaker attraction of nucleus
  3. shielding - electrons in outer shells are repelled by electrons in complete inner shells = weaker attraction of nucleus
• factors affecting IE are nuclear attraction, atomic radius and shielding
• Cl in drinking water

  1. kills bacteria
  2. reduced growth of algae
  3. toxic
  4. can form chlorinated hydrocarbons
• concentration on equilibrium

  1. increasing reactants - products
  2. decreasing reactants - reactants
  3. increasing products - reactants
  4. decreasing prducts - products
• endothermic

  1. energy is transferred from surroundings to system
  2. bond breaking
  3. positive enthalpy change
• exothermic

  1. energy is transferred from system to surroundings
  2. bond making
  3. negative enthalpy change
  4. eg combustion, oxidation of carbohydrates (glucose in respiration)
• factors affecting strength of metallic bond

  1. more protons = stronger as stronger nuclear attraction
  2. more delocalised electrons per atom = stronger as outer shell electrons are delocalised
  3. smaller ion = stronger as closer to nucleus
• first ionisation energy is the energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms H(g) → H+(g) + e-
• observations from the displacement reactions of the halide ions by halogens if organic solvent is added

  A) colourless

  B) iodine

  C) purple

  D) yellow

  E) displaced

  
• observations from the displacment reactions of the halide ions by halogens

  A) brown

  B) yellow

  C) brown

  D) no reaction

  E) green

  
• ionisation energies down group 2 decrease because

  1. takes less energy to remove the electrons as they become further away from the positive nucleus
  2. nucleus is more effectively shielded by more inner shells of electrons
• Sr's second ionisation is greater than the first as it requires more energy to remove an electron from a cation than it is from a neutral atom
• properties of group 2 elements

  1. giant metallic structure - high mpt
  2. going down the group, electrons in the sea of delocalised electrons are further away from the positive nuclei therefore the strength of metallic bonds decreases
• formation of hydroxides

  1. with liquid Mg + 2H2O → Mg(OH)2 + H2 (effervescence)
  2. with steam Mg + H2O → MgO + H2 (white solid)
  3. extraction of titanium  Mg + TiCl4 → 2MgCl2 + Ti
  4. Mg is expensive and high temperature is needed
• solubility of hydroxides and sulphates

  1. hydroxides - slightly soluble Mg → Ba soluble (solubility increases)
  2. sulphates - soluble Mg → Ba insoluble (solubility decreases)
• uses of magnesium

  1. extract titanium
  2. Mg(OH)2 can be used to neutralise stomach acid for indegestion because its sparingly insoluble (antacids)
• uses of calcium

  1. Ca(OH)2 is partially soluble in water and will appear as a white precipitate
  2. used in agriculture to neutralise acid soils 
  3. Ca(OH)2 (aq) is limewater which will turn cloudy in a solution with carbon dioxide as white calcium carbonate is produced
  4. can be used to remove SO2 from the waste gases from furnaces by flue gas desulfurisation (neutralisation)
• uses of barium

  1. BaCl is used as a test for sulphates: add dilute HCl then white precip forms