Module 3

• Periodicity


  Repeating, periodic pattern across a period
• First Ionisation Energy


  Energy required to remove one electron from one mole of gaseous atoms, forming one mole gaseous 1+ ions
• Factors Affecting Ionisation Energy

  1. Atomic Radius

  2. Nuclear Charge

  3. Electron Shielding
• Down a Group


  1. Atomic radius increases

  2. Shieling increases

  3. Nuclear charge decreases

  4. 1st ionisation energy decreases
• Across a Period


  1. Nuclear charge increases

  2. Similar shielding

  3. Atomic radius increases

  4. 1st ionisation energy increases (except period 2&3)
• Metallic Bonding


  Strong electrostatic attraction between cations and delocalised electrons (cations fixed, delocalised electrons mobile)
• Properties of Metallic Bonding

  1. Conducts electricity

  2. high melting & boiling point

  3. Insoluble
• Giant Covalent Lattice


  Many billions of atoms held together by a network of strong covalent bond (boron, carbon, and silicon)
• Properties of Giant Covalent Lattice's

  1. High melting & boiling points

  2. Insoluble in almost all solvents

  3. Conduct electricity depending on form of lattice
• Graphene


  1. Single layer of graphite

  2. Hexagonally arranged carbons

  3. Conducts electricity

  r. Thinnest and strongest material in existence
• Graphite


  1. Parallel layers of hexagonally arranged carbons

  2. Layers bonded by London Forces

  3. Spare delocalised electron between each layers
• Diamond


  Diamond is a giant covalent lattice of carbon atoms

  Each carbon is covalently bonded to four others in a tetrahedral arrangement with a bond angle of 109.5 degrees

  The result is a giant lattice structure with strong bonds in all directions
• Most Common Reactions of Group 2

  Redox (act as reducing agents)
• Group 2 Reaction with Oxygen


  Metal + Oxygen = Metal Oxide
• Group 2 Reaction with Water


  Metal + Water = Metal Hydroxide + Hydrogen
• Group 2 Reaction with Dilute Acids

  Metal + Acid = Salt +Hydrogen
• Salt


  The H+ ion in an acid has been replaced by a metal ion
• How a hydroxide ion in aquaeos solution acts as a base during neutralisation

  It accepts a proton or accepts H+
• Oxides Reaction with Water


  Metal Oxide + Water = Metal Ion + Hydroxide Ion
• Group 2 compounds in Agriculture

  Calcium hydroxide is added to fields as lime by farmers to increase pH of acidic soil

  
  

  Ca(OH)2 + 2H^+ = Ca^2+ + 2H2O
• Group 2 compounds in Medicine

  Group 2 basess are used as antacids for treating acid indegestion

  
  

  Mg(OH)2 + 2HCl = MgCl2 + 2H2O

  CaCO3 + 2HCl = CaCl2 + H2O + CO2
• Halogens at RTP


  Fluorine = Pale yellow gas

  Chlorine = Pale green gas

  Bromine = Red-brown liquid

  Iodine = Shiny grey-black solid
• Trend in B.P. Down Group 7

  1. More electrons

  2. Stronger London forces

  3. More energy needed to break intermolecular forces

  4. BPT increases
• Halogen-halide displacement reaction


  Bromine ions displace Chlorine

  Cl2 + 2Br^- → 2Cl^- + Br2

  Iodine ions displace chlorine

  Cl2 + 2I^- → 2Cl^- + I2

  Iodine ions displace Bromine

  Br2 + 2I^- → 2Br^- + I2
• Reaction of chlorine with water

  Cl2 + H2O → HClO + HCl
• Reaction of chlorine with cold, dilute aqueous sodium hydroxide

  Cl2 + 2NaOH → NaClO + NaCl + H20
• Reaction of chlorine with hot concentrayed sodium hydroxide


  3Cl 2 + 6NaOH → NaClO3 + 5NaCl + 3H2O
• Benefits and risks of chlorine use

  benefits - Disinfects water from bacteria

  risks - chlorine can react with organic hydrocarbons in water forming chlorinated hydrocarbons which are carcinogenic
• Halogens in Cyclohexane


  Cl = Pale green

  Br = Orange

  I = Violet
• Trend in Reactivity Down Group 7

  1. Atomic radius increases

  2. Shielding increases

  3. Reactivity decreases (become weaker oxidising agents down the group)
• Disproportionation


  Redox reaction where the same element is both oxidsed and reduced
• Carbonate Test


  1. Add dilute nitric acid to solution

  Na2CO3 + 2HNO3 → 2NaNO3 + CO2 + H2

  2. Test bubbles produced by bubbling through limewater

  3. CO2 is present if limewater turns cloudy

  CO2 + Ca(OH)2 → CaO + H2O
• Sulphate Test


  1. Add barium chloride/ barium nitrate

  2. White precipitate produced if present as barium sulfate is produced

  Ba^2+ SO4^2- → BaSO4
• Halide Test


  - Add AgNO3 to aqueous halide solution

  Ag+ + X- → AgX

  - Cl = white, Br = cream, I = yellow

  - Use aqueous dilute and concentrated ammonia to test solubility

  - Cl = soluble in dilute, Br = soluble in in conc, I = insoluble in dilute and conc
• Sequence of tests


  Carbonate, CO3^2-

  Sulfate, SO4^2-

  Halides, Cl-, Br-, I-
• Test for Ammonium Ion

  1. Add NaOH to solution

  2. Ammonia gas gets produced

  3. Warm mixture to release gas

  4. Moist indicator paper will turn blue if positive
• Enthalpy


  Measure of heat energy in a chemical system
• Chemical System


  The atoms, molecules, or ions making up the chemicals
• Enthalpy Change Equation


  EC = H(products) - H(reactants) (can be positive or negative)
• Exothermic


  System releases heat energy to surroundings (enthalpy change will be positive)