topic 04 - period 3 and their oxides

• which row are the period 3 elements?

  3rd row
• what trends occur across period 3?

  • trends in reactivities of the elements with oxygen and water
  • trends in the reactivities of their oxides with watrer
• which are the only period 3 elements to react with cold water?

  sodium and magnesium
• what occurs when solid sodium is added to water at room temp?

  • there is an immediate reaction
  • produces aqueous sodium hydroxide and gaseous hydrogen
  • the aqueous sodium hydoxide is strongly alkaline
• what observations are made when sodium is added to water?

  • sodium would dissolve and float on the water's surface
  • fizzing and effervescence seen in the solution as hydrogen gas released
• what would happen when adding universal indicator to the solution of aqueous sodium hydroxide?

  the solution would turn a dark blue/purple colour
• what would happen when we use a pH probe on the solution of sodium hydroxide?

  pH probe would show the solution has a pH between 13.00 and 14.00
• what would happen if we add magnesium to water?


  • produces aqueous magnesium hydroxide and gaseous hydrogen
  • rate of reaction is very slow so only a few bubbles of hydrogen may be produced over a few days
  • this shows magnesium is less reactive than sodium
  • magnesium hydroxide is sparingly soluble so very few of the hydroxide ions are released into the solution so the aqueous magnesium hydroxide made is weakly alkaline.
• what is the equation showing the reaction of sodium with water?


  2Na (s) + 2H2O (l) --> 2NaOH (aq) + H2 (g)
• what is the equation showing the reaction of magnesium with water?

  Mg (s) + 2H2O (l) --> Mg(OH)2 (aq) + H2 (g)
• what observations can be made when magnesium is added to water?

  • magnesium dissolving and floating on the surface of the water
  • fizzing or effervescence seen in the solution as hydrogen is released
• what would happen as a pH probe is placed into the solution of magnesium hydroxide?

  • pH probe will show a pH of 9.00 to 10.00
• what happens when solid magnesium is heated and reacted with steam?

  • a much faster reaction occurs
  • produces solid magnesium oxide and hydrogen gas
• what is the equation of solid magnesium reacted with steam?

  Mg (s) + H2O (g) --> MgO (s) + H2 (g)
• what observations can be made when solid magnesium reacts with steam?

  • magnesium dissolving and floating on the surface of the water
  • a white powder being formed (the magnesium oxide)
  • fizzing or effervescence being seen in the solution as hydrogen gas is released
• all the reactions (magnesium w/ water, sodium w/ water and magnesium w/ steam) are examples of what?

  all are examples of redox reactions