inorganic - periodicity

Question 1

the elements

Answer 1

• Sodium (Na), Magnesium (Mg) and Aluminium (Al)
  they are metallic, shiny when exposed to air, conduct electricity and react with dilute acids to give hydrogen and salts
• Silicon (Si)
  is a semi-metal (metalloid), it conducts electricity to some extent
• Phosphorus (P), Sulphur (S) and Chlorine (Cl)
  they are non metals, they do not conduct electricity and have low melting+boiling points
• Argon (Ar)
  is a noble gas, chemically unreactive (inert) and exists as separate atoms

Question 2

redox reactions of the elements

Answer 2

• every element starts with an oxidation number of zero, and after it has reacted, ends up with a positive or negative oxidation number

Question 3

reaction with water - sodium

Answer 3

• reaction is vigorous - sodium floats on the surface then fizzes rapidly due to the heat energy released by the reaction
• a strongly alkaline solution of NaOH (Sodium Hydroxide) is formed - pH = 13-14
  0 +1 -2 +1 -2 +1 0
  2Na(s) + 2H2O(l) –> 2NaOH(aq) + H2(g)

Question 4

reaction with water - magnesium

Answer 4

• reaction is very slow at room temperature
• the resulting solution is less alkaline than in the case of sodium
• because magnesium hydroxide is less soluble - pH = 10
  0 +1 -2 +2 -2 +1 0
  Mg(s) + 2H2O(l) –> Mg(OH)2 (aq) + H2(g)
• but reaction is much faster with heated magnesium and steam
• resulting in magnesium oxide and hydrogen
  0 +1 -2 +2 -2 0
  Mg(s) + H2O(g) –> MgO(s) + H2(g)

Question 5

reaction with oxygen

Answer 5

• all period 3 elements, except Argon, react with oxygen
• it is an exothermic reaction
• oxidation state of period 3 elements increase moving across the period - except for sulphur
• and that of oxygen decrease 0 -> -2

Question 6

reaction with oxygen - sodium

Answer 6

• sodium burns slightly in air
• yellow flame
• white sodium oxide solid formed
  0 0 +1 -2
  2Na(s) + 1/2O2(g) –> Na2O(s)

Question 7

reaction with oxygen - magnesium

Answer 7

• a strip of magnesium ribbon burns in air
• white bright flame
• white powder of magnesium oxide produced
  0 0 +2 -2
  2Mg(s) + O2(g) –> 2MgO(s)

Question 8

reaction with oxygen - aluminium

Answer 8

• aluminium powder is heated, then lowered into a gas jar of oxygen - it burns brightly
• white powder of aluminium oxide
  0 0 +3 -2
  4Al(s) + 3O2(g) –> 2Al2O3(s)

Question 9

reaction with oxygen - silicon

Answer 9

• heated strongly in oxygen
• silicon oxide formed
  0 0 +4 -2
  Si(s) + O2(g) –> SiO2(s)

Question 10

reaction with oxygen - phosphorus

Answer 10

• red phosphorus heated
• it reacts with oxygen releasing white smoke of phosphorus pentoxide
• red and white phosphorus are allotropes of phosphorus
  the same element, with atoms arranged differently
  0 0 +5 -2
  4P(s) + 5O2(g) –> P4O10(s)

Question 11

if the supply of oxygen is limited when reacting with phosphorus, what is formed?

Answer 11

phosphorus trioxide P2O3

Question 12

reaction with oxygen - sulphur

Answer 12

• sulphur power is heated, then lowered into a gas jar of oxygen
• blue flame
• colorless gas sulphur dioxide formed
  0 0 +4 -2
  S(s) + O2(g) –> SO2(g)