1. Periodicity & group 2

• Periodicity is the study of trends within the periodic table
• Along a period, atomic radius decreases

  • This is due to an increased nuclear charge
  • The outer electrons are pulled in closer to the nucleus as the increased charge produces a greater attraction
• Down a group, atomic radius increases

  • This is due to an added electron shell which increases the distance between outer electrons and the nucleus
• Along a period, ionisation energy increases

  • Stronger attraction due to smaller atomic radius so more energy required
• Down a group, ionisation energy decreases
• A higher charged ion will result in a higher melting point

  • This is because more electrons are released as free electrons so the attractive electrostatic forces increase from Na to Al
• Strong covalent structures have high melting points as the covalent bonds require a lot of energy to break
• Simple covalent molecules are held with weak van der waals forces which dont need much energy to overcome - low mp
• Noble gases are very stable and the vdw forces between them are weak - low mp
• Reactions with water

  • Reactivity increases down the group.
  • Beryllium doesn’t react.
  • Calcium, strontium and barium all react with cold water to give metal hydroxide and hydrogen. 
  • A white precipitate of hydroxide is formed.  
  • Less precipitate is formed down the group as the hydroxide gets more soluble down the group.
• Mg+ 2H2O(l) -> Mg(OH)2 + H2

  Mg + H20(g) -> MgO + H2O
• Magnesium reaction with steam

  Mg + H20(g) -> MgO + H2O

  • the hydroxide isn’t stable at higher temperatures and decomposes to give the oxide and water
• Solubility of sulfates

  • Less soluble in water as you go down the group.
  • The metal ion can be added to sodium sulfate.  White precipitates  are formed.  
  •  Adding barium ions can be used to test for sulfates
• When an atom loses an electron to form a cation, the other electrons are more attracted to the nucleus, and the radius of the ion gets smaller
• For group 2 metals, the melting point decreases as you go down the group
• With group 2, solubility of hydroxides increases down the group
• With group 2, solubility of sulfates decreases down the group
• The insolubility of barium sulfate means its very useful in medicine as barium meals
• The insolubility of magnesium hydroxide means its very useful in medicine as an antacid as it is alkaline and can neutralise acids
• Barium chloride is used as a test for sulfate ions as it reacts to form barium sulfate which forms as a white precipitate when sulfate ions are present
• Barium sulfate can be used in medicine to produce an X-ray image
• Magnesium is used in the extraction of titanium from titanium chloride via a displacement reaction

  TiCl4 + 2Mg -> 2MgCl2 + Ti
• Calcium oxide reacts with sulfur dioxide to remove it from factory pollutants and prevent it from being released into the atmosphere

  • This forms sulfite and water
• An element like nickel is ductile because layers of ions can slide over one another
• Metals conduct electricity because delocalised electrons flow through metal
• fill

  A) nuclear charge

  B) outer electrons

  C) charge

  D) attraction

  
• Flue gases are gases produced by power stations which are harmful to the environment
• Ca(OH)2 is used to neutralise soil
• fill in

  A) HCl

  B) acidify

  C) BaCl2

  D) White

  
• When magnesium reacts with steam there is a bright/white light and white powder produced
• Group 2 elements react with water to form bases
• Reactivity increases with water down the group
• As a general rule:

  If the negative ion has a double charge (eg SO4 2-), they become less soluble going down the group
• fill

  A) calcium hydroxide

  B) magnesium hydroxide

  
• Barium compounds are toxic - however because barium sulfate is insoluble, it can't be absorbed into the blood
• titanium ore is converted to titanium chloride by heating with carbon and chlorine gas
• purified titanium chloride is reduced using magnesium