chapter 8

• Group 2 elements have two electrons in the outer shell that are oxidised to form 2+ ions. They are known as reducing agents. They form metal oxides with oxygen, hydroxides with water, and salts with dilute acids
• Reactivity increases down the group and ionisation energies decrease. This is because increased shielding increases atomic radius, decreasing nuclear attraction, so the electrons required less energy to be lost and are lost easier, so they become more reactive
• group 2 hydroxides increase in solubility down the group and the solutions become more alkali
• group 2 bases are used in agriculture to neutralise the PH of soil in fields, such as calcium hydroxide. They are used in medicine to treat acid indigestion. This includes calcium and magnesium carbonates, and also magnesium hydroxide.
• The group 7 elements are also know as the halogens and have 7 electrons in their outer shells. They all exist as diatomic molecules at RTP
• Group 7 boiling points increase down the group, as more electrons cause stronger london forces which require more energy to break
• halogens are reduced usually in redox reactions and are called oxidising agents
• reactivity of halogens decrease down the group as the outer shell gets further from the nucleus, so its harder to gain an electron. Displacement reactions can be used to show the reactivity as cl2 can displace br- and I- out of halide compounds, and br2 can displace i- out of its halide compounds
• halogens in water

  chlorine= pale green

  bromine=orange

  iodine=brown

  halogens in cyclohexane

  chlorine=pale green

  bromine=orange

  iodine=violet
• reactivity decreases down group 7 as atomic radius increases, so shielding increases, weaking nuclear attraction to capture electrons
• a disproportionation reaction is when the same element in reduced and oxidised at the same time
• when chlorine reacts with water, it forms hydrochloric acid and chloric(I) acid, which is a weak bleach

  when chlorine reacts with cold dilute sodium hydroxide, it forms water sodium chloride and sodium chlorate, which is found in household bleach.
• chlorine kills bacteria in water to make it safe to drink but is extremely toxic in large amounts, and can be a respiratory irritant.
• qualitative analysis relies on observations and interviews to gather data, while quantitative analysis relies on numerical data
• carbonate test:

  carbonates react with nitric acid to form carbon dioxide

  the carbon dioxide is tested by being bubbled through limewater
• sulfate test:

  barium nitrate is reacted with compound, if a white precipitate forms its a sulfate. The precipitate is barium sulfate.
• halide tests:

  add silver nitrate and observe the precipitates

  white=cl cream=br yellow=I

  if the precipitate dissolves in dilute ammonia its a chloride, and if it dissolves in concentrated ammonia its a bromine.
• ammonium ion test

  sodium hydroxide is added to produce ammonia gas, which is tested with moist ph indicator paper, which turns blue