3.2.4 Properties of Period 3 elements and their oxides

• Reactions of period 3 elements with water

  Only Sodium, magnesium and Chlorine react with water. Aluminium and silicon do not react with water

  > Both elements are covered with a thin layer of their oxides Aluminium oxide / silicon dioxide

  > the oxide prevents water from reaching the inner atoms as the oxide is insoluble
• Reactions of period 3 elements with water

  Sodium reacts violently with water

  observations: orange flame, fizzing, melts into a ball , skates across surface

  2Na + 2H2O -> 2NaOH + H2

  Magnesium reacts slowly with water

  Mg + 2H2O -> Mg(OH)2 + H2 Mg(OH)2 has a ph of 8 - 10

  however reacts violently with steam

  Mg + H2O -> MgO + H2

  observation bright white flame and solid
• Reactions of period 3 with oxygen

  Chlorine and Argon do not react with Oxygen
• Reactions of period 3 with oxygen

  Sodium, Na

  Word: Sodium+ oxygen -> Sodium oxide

  Symbol: 4 Na + O2 → 2 Na2O

  Observation: Yellow flame , white sodium oxide

  Magnesium, Mg

  word: Magnesium + oxygen→ Magnesium oxide

  Symbol: 2 Mg + O2 → 2 MgO

  Observation: bright White flame, white solid (Mgo)

  Aluminium, Al

  word: Aluminium + Oxygen → Aluminium oxide

  Symbol: 4 Al + 3 O2 → 2 Al2O3

  Observation: White solid (Al2O3) / White flame
• Reactions of period 3 with oxygen

  Silicon, Si

  Word: Silicon + Oxygen → Silicon dioxide /Silicon(IV) oxide

  Symbol: Si + O2 -> SiO2 (empirical formula)

  Observation: White flame , White solid

  Phosphorus, P

  Word: Phosphorus + Oxygen → phosphorus (V) oxide

  Symbol: 4 P + 5 O2 → P4O10

  Observation: White solid, bright white flame.

  Sulfur, Si

  Word: Sulfur + oxygen → sulfur dioxide

  Symbol: S + O2 → SO2. Leads to acid rain

  observation: blue flame

  another equation

  word: Sulfur + Oxygen -> Sulfur (VI) oxide / trioxide

  Symbol: 2 S + 3 O2 -> 2 SO3
• Phosphorus Oxide is represented by P4O10 rather than P2O5

  > This is because one molecule of phosphorus (V) oxide is made up of 4 phosphorus and 10 oxygens atoms.
• Melting point of period 3 oxides

  The melting points of the oxides increase from Sodium oxide (Na2O) to magnesium oxide (MgO) and then decreases
• Na2O, MgO , Al2O3

  Type of bonding: lonic bonding

  Type of Structure: Giant ionic lattice

  Explaination. They have high melting point because there are strong electrostatic force of attraction between oppositely charged ions therefore a lot of energy is needed to break the ions .
• Why does MgO have a higher melting point than Na2O

  Mg2+ are smaller and highly charged compared to Na+ ions.

  Therefore there is stronger attraction between the Mg2+ ions and the O2- ions compared to Na+ and O2- ion.

  Therefore more energy is required to break the ion
• Al2O3

  Type of banding: lonic with covalent character

  Al3+ ions are smaller and highly charged compared to Mg2+ ions. The Al3+ ions polarise the oxide ions. Therefore aluminium oxide has ionic bonding with covalent character
• SiO2

  Type bonding: covalent bonding

  Type Structure: Giant Covalent

  > SiO2 has a giant covalent Structure

  > Silicon dioxide has a high melting point as a large number of strong covalent bonds needs to be broken
• P4O10

  Type bonding: Covalent bonding

  Type Structure: Simple molecular

  QOL: Weak intermolecular Van der Waals forces between the molecules

  > As phosphorus oxide is a large molecule there are lots of weak Van der Waals forces between molecules and therefore it is a solid at room temp
• SO2 /SO3

  Type of bonding: Covalent bonding

  Type of structure: simple molecular structure

  The van der Weals forces between the SO3/SO2 molecules are weaker between molecule as they are smaller. Therefore Van der Waals force is weaker so SO3 is a liquid and SO2 is a gas at room temperature
• Electrical conductivity

  Na2O ,MgO, Al2O3 can conduct electricity when molten.

  Na2O will dissolve in water so ions are free to move and will conduct electricity.

  MgO, Al2O3 are insoluble in water and won't conduct electricity
• Electrical conductivity

  > SiO2 is also insoluble and covalent compound and doesn't conduct electricity.

  > P4O10, SO2, SO3 are covalent compounds and do not conduct electricity.

  > P4O10, SO2 , SO3 → When added to water reacts to form an acid, H+, which conduct electricity.
• How would you distinguish SO2 and SO3

  Reagent: Dissolve SO2 and SO3 in water separately. test the pH of the solution formed using a pH meter.

  Observation: SO2 forms H2SO3 sulfurous acid which has a pH between 2 - 3

  SO3 forms H2SO4 sulfuric acid which has a pH between 1 - 0
• Reactions of Period 3 oxides with water

  Aluminium oxide (Al2O3) and silicon oxide (SiO2) are insoluble and so pH remains 7
• Reactions of Period 3 oxides with water (Metals -> metal hydroxides)

  > Na2O, Sodium oxide

  Word: Sodium oxide + Water → Sodium hydroxide

  Symbol: Na2O + H20 -> 2 NaOH ( pH : 12 - 14 )

  > MgO, Magnesium oxide ( sparingly soluble )

  Word: Magnesium oxide + water → Magnesium hydroxide

  Symbol: MgO + H2O -> Mg(OH)2 ( pH : 9 - 10 )
• Reactions of Period 3 oxides with water ( non-metals -> acids)

  > P4O10 Phosphorus (V) oxide

  Word: Phosphorus (v) oxide + water → phosphoric acid

  Symbol: P4O10 + 6H20 → 4H3PO4 ( pH: 0 - (-1) )

  > SO2, Sulfur (IV) oxide / sulfur dioxide

  Word: Sulfur (IV) oxide + water -> Sulfurous acid

  Symbol: SO2 + H20 -> H2SO3 ( pH: 2 - 3 )

  > SO3 , Sulfur (VI) oxide

  Word: Sufur (VI) oxide + water → Sulfuric acid

  Symbol: SO3 + H2O -> H2SO4 ( pH: 0 - 1 )
• Reactions with acids and bases

  Sodium oxide

  Word: Sodium oxide + Hydrochloric acid -> Sodium Chloride + Water

  Symbol: Na2O + 2 HCl → 2 NaCl + H2O

  Word: Sodium oxide + Sulfuric acid → Sodium Sulfate + Water

  Symbol Na2O + H2SO4 → Na2SO4 + H2O

  Magnesium oxide

  Word: Magnesium oxide + hydrochloric acid -> Magnesium chloride + water

  Symbol: MgO + 2 HCl -> MgCl2 + H2O

  Word: Magnesium oxide + phosphoric acid → magnesium phosphate + water

  Symbol : 3 MgO + 2 H3PO4 -> Mg3(PO4)2 + 3 H2O
• Reactions with acids and bases

  Aluminium oxide is amphoteric so can react with acids and bases

  Al2O3 as a base

  Word: Aluminium Oxide + hydrochloric acid -> Aluminium chloride + water

  Symbol: Al2O3 + 6 HCl -> 2 AlCl3 + 3 H2O

  Al2O3 as an acid

  Symbol: Al2O3 + 2 NaOH + 3 H2O -> 2 NaAl(OH)4
• Reactions with acids and bases

  Silicon (IV) oxide

  Symbol: SiO2 +2 NaOH → Na2SiO3 + H2O

  Phosphors (V) oxide

  step 1: P4O10 + 6 H2O -> 4 H3PO4

  step 2: 4 H3PO4 + 12 NaOH -> 4 Na3PO4 + 12 H2O

  overall : P4O10 + 12 NaOH -> 4 Na3PO4 + 6 H2O

  Sulfur (IV) oxide

  step 1: SO2 + H2O -> H2SO3

  step 2: H2SO3 + 2 NaOH → Na2SO3 + 2 H2O

  overall: SO2 + 2 NaOH → Na2SO3 + H2O

  Sulfur (VI) oxide

  step 1: SO3 + H2O → H2SO4

  step 2: H2SO4 + 2 NaOH → Na2SO4 + 2 H2O

  overall: SO3 + 2 NaOH → Na2SO4 + H2O
• Acids and Anions Structure

  Phosphoric(V) acid, H3PO4

  A) H2PO4 -

  B) HPO4 2-

  C) PO4 3-

  
• Acids and Anions Structure

  Sulfurous acid, H2O3

  A) H2SO3

  B) HSO3 -

  C) SO3 2-

  
• Acids and Anions Structures

  Sulfuric acid, H2SO4

  A) H2SO4

  B) HSO4 -

  C) SO4 2-