Properties of Period 3 elements and oxides

how does sodium react with water, what can be observed, what is made

• reacts vigorously with water

• forms a ball and fizzing

• produces hydrogen gas and an alkaline solution

equation for sodium and water

2Na (s) + 2H2O (l) → 2NaOH (aq) + H2 (g)

how to test for the presence of hydrogen gas produced in reaction between sodium and water

squeaky pop produced with a lighted splint

how to test for the alkaline solution formed in the reaction between sodium and water

litmus paper

universal indicator

which element is more reactive: sodium or magnesium

sodium

why is sodium more reactive than magnesium

• Na loses 1 electron to produce Na+

• Mg needs to lose 2 electrons, to form Na2+, which requires more energy to remove 2

how does magnesium react with water, what is produced

• reacts slowly with water

• Mg(OH)2 produced

• hydrogen gas produced

why does magnesium react slowly with water

weak alkaline solution produced, magnesium hydroxide, which is sparingly soluble, meaning little OH- ions in the solution,

equilibrium lies to the left

reaction between magnesium and liquid water

Mg (s) + 2H2O (l) → Mg(OH)2 (aq) + H2 (g)

how does magnesium react with steam

• reacts much faster with steam

• forms magnesium oxide, MgO

equation between magnesium and steam

Mg (s) + H2O (g) → MgO (s) + H2 (g)

magnesium OXIDE produced

difference between magnesium reacting with water and steam

• reacts slowly with water, produces a hydroxide

• reacts quickly with steam, produces an oxide

when period 3 elements react with oxygen, what is produced

oxides

exception in period 3 of reacting with oxygen to form an oxide

sulfur: it produces sulfur dioxide, or sulfur trioxide

under what conditions is sulfur trioxide produced when oxygen and sulfur react

under high temperature and a catalyst,

SO3, oxygens oxidation started is +6

equation between sodium and oxygen

2Na (s) + ½ O2 (g) → 2Na2O (s)

equation between magnesium and oxygen

Mg (s) + ½ O2 (g) → MgO (s)

equation between aluminium and oxygen

2Al (s) + 1 ½ O2 (g) → Al2O3 (s)

equation between silicon and oxygen

Si (s) + O2 (g) → SiO2 (s)

equation between phosphorus and oxygen

P4 (s) + 5O2 (g) → P4O10 (s)

two possible equations for reaction between sulfur and oxygen

S (s) + O2 (g) → SO2 (g)

2S (s) + 3O2 (g) → 2SO3 (g)

how does sodium react with air, what is produced

reacts quickly with air,

forms Na2O

how does magnesium react with air, what is produced

reacts very fast with air,

forms MgO

how does aluminium react with air, what is produced

slow reaction with air, unless powdered,

forms Al2O3

how does silicon react with air, what is produced

slow reaction with air,

forms SiO2

how does phosphorus react with air, what is produced

spontaneously combusts, any small amount of heat can trigger it,

forms P4O10

how does sulfur react with air, what is produced

steadily burns,

forms SO2

what does structure and bonding of oxides affect

melting point

why does Na2O, MgO and Al2O3, metal oxides, have the highest melting points

they form giant ionic lattices,

lots of strong electrostatic forces of attraction between oppositely charged ions, which require a lot of energy to break

which of the metal oxides has the highest melting points

magnesium oxide, MgO

why does magnesium oxide have the highest melting point compared to SODIUM

Mg2+ has a larger cation than Na+,

2+ ions attract more strongly to the oxygen

why does magnesium oxide have a higher melting point than aluminium oxide

Al2O3 has a lower melting point,

Al3+ ions distort the electron cloud of oxygen = a little covalent character (not purely ionic / less ionic characteristics) = less energy required to break bonds

how does Al3+ distort the electron cloud of oxygen

high cationic charge = pulls electrons towards itself

which non metal oxide has the highest melting point

sulfur dioxide, SiO2

why does sulfur dioxide have a higher melting point than P4O10 and SO2

SiO2 forms a macromolecular structure, meaning it has many strong, covalent bonds, which require a lot of energy to break

why does phosphorus oxide and sulfur dioxide have the lowest melting points in period 3

they form simple molecular structures = weaker intermolecular forces, which require less energy to break

order of period 3 oxides from highest melting point to the lowest

MgO > Al2O3 > SiO2 > Na2O > P4O10 > SO2

when ionic oxides, Na and Mg, react with H2O, what if formed

an alkaline solution

how is this alkaline solution formed

ionic oxides contain O 2- ion,

this ion accepts protons from water molecules when dissolved in solution

equation between sodium oxide and water

Na2O (s) + H2O (l) → 2NaOH (aq)

what is the pH of the solution formed when sodium oxide reacts with water

12-14

why is a strong alkaline solution formed when sodium oxide reacts with water

NaOH is a strong base, so dissolves readily = more dissociation = more OH- ions in solution

how does magnesium oxide, MgO, react with water, what is formed

dissolves sparingly in water,

forms magnesium hydroxide, Mg(OH)2 (aq)

pH of alkaline solution formed when magnesium oxide reacts with water

9-10

why is a weaker alkaline solution formed when magnesium oxide and water react

MgO dissolves sparingly in water, so less dissociation, so less OH- ions

equation of magnesium oxide and water

MgO (s) + H2O (l) → Mg(OH)2 (aq)

what is formed when simple covalent oxides, P and S, react with water

acidic solutions,

pH 0-2

what conditions are assumed for simple covalent oxides to form an acidic solution with the pH 0-2

assumed minimum concentration of moles used (1dm-3)

reaction between phosphorous oxide and water

P4O10 (s) + 6H2O (l) → 4H3PO4 (aq)

• phosphoric acid formed

dissociation equation of phosphoric acid

H3PO4 (aq) → 3H+ (aq) + PO4 2- (aq)

H+ and -ve ions produced = conjugate bases

how is phosphoric acid a triprotic acid

3 protons are produced per phosphoric acid molecule