Chapter 8 REACTIVITY TRENDS

• What ions do group 2 atoms form?

  2+ ions from the s2 orbital
• Why does reactivity increase down group 2?

  Outer electrons further away from nucleus so less energy needed to remove them
• What is the link between first ionisation energy and reactivity in group 2?

  As ionisation energy decreases, reactivity increases because of decreases attraction between the nucleus and electrons from shielding
• What forms when group 2 metals react with water?

  Form metal hydroxides which act as bases
• What does magnesium form when reacted with water?

  Magnesium oxide, MgO
• Why are group 2 elements reducing agents?

  They cause another species to be reduced
• What properties of group 2 (hydr)oxides allow them to neutralise acids?

  They readily dissociate into OH- ions
• What are some uses of group 2 (hydr)oxides?

  Neutralise acidic soils (CaO)

  Neutralise excess stomach acid - antacid tablets (Mg(OH)2)
• What colour and state is Fluorine at room temperature?

  Pale yellow gas
• What colour and state is Chlorine at room temperature?

  Pale green gas
• What colour and state is Bromine at room temperature?

  Orange-brown liquid
• What colour and state is Iodine at room temperature?

  Grey solid
• Why are halogens oxidising agents?

  They cause another species to become oxidised
• Why does boiling point increase down group 7?

  Induced dipole-dipole forces increases because the size and Mr increases
• Why does electronegativity decrease down group 7?

  Atomic radius increases and the distance between the positive nucleus & negative electrons increases therefore the ability to attract another electron decreases (more shielding)
• What reactions take place between halogens & halide ions and how can this be observed?

  Displacement reactions take place and a colour change will be observed if it does
• What type of solvent is used commonly in displacement reactions and why?

  Non-Polar organic solvent (e.g. cyclohexane) to observe the colour change better as halogens dissolve in it more readily than water
• How does a displacement reaction happen?

  When a more reactive halogen displaces a less reactive halide ion

  e.g. Chlorine will displace bromide ions
• What is observed when Chlorine reacts with bromide ions?

  Colour change to orange as bromine is formed
• What is observed when Chlorine reacts with iodide ions?

  Colour change to violet as iodine is formed
• What is observed when Bromine reacts with chloride ions?

  No reaction
• What is observed when Bromine reacts with iodide ions?

  Colour change to voilet as iodine is formed
• What is observed when Iodine reacts with chloride ions?

  No reaction
• What is observed when Iodine reacts with bromide ions?

  No reaction
• What test can be carried out to confirm the presence of halide ions?

  Silver nitrate test and confirmed with ammonia solution
• What do chloride ions produce when tested with silver nitrate and how is it confirmed?

  White precipiate and confirmed if this dissolves forming a colourless solution with dilute ammonia
• What do bromide ions produce when tested with silver nitrate and how is it confirmed?

  Cream precipitate and confirmed if it dissolves forming a colourless solution with concentrated ammonia
• What do iodide ions produce when tested with silver nitrate and how is it confirmed?

  Yellow precipitate and confirmed if it remains when concentrated ammonia is added (silver iodide is insoluble)
• How do you test for ammonium containing compounds?

  Add sodium hydroxide, heat gently and ammonia gas is given off which turns damp litmus paper blue
• How do you test for the presence of hydroxides?

  Hydroxides are alkaline and will turn red litmus paper blue, however this isn't a pure test as another alkalis will turn it blue as well
• How do you test for carbonates?

  Add acid to the test tube and the mixture will effervesce. To confirm this is carbon dioxide, bubble it through limewater and it will turn cloudy
• How do you test for sulphates?

  Add HCl first to ensure no carbonates are present then add barium chloride (barium nitrate if halide test taking place after) and a positive result forms a white precipitate (barium sulphate) which is insoluble
• What is the correct sequencing for carrying out the qualitative tests and why?

  1. Carbonates

  2. Sulphates (using barium nitrate)

  3. Halides

  To ensure there are no false positives