Period 3 Elements Flashcards
Between sodium and magnesium, which is more reactive?
sodium
less energy is required to remove an electron
Reaction of sodium with water
-sodium reacts vigorously with cold water
-forms ball and fizzing
2Na (s) + 2H2O(l) –> 2NaOH (aq) + H2 (g)
Reaction of magnesium with water
-magnesium reacts slowly with cold water
-Mg(OH)2 is sparingly soluble
-hence little OH- ions in solution
Mg (s) + 2H2O(l) –> Mg(OH)2 (aq) + H2 (g)
What do period 3 elements form when they react with oxygen?
Give equations for Na-P
What is the exception and why?
oxides
2 Na (s) + 1/2 O2 (g) –> Na2O (s)
Mg (s) + 1/2 O2 (g) –> MgO (s)
4 Al (s) + 3 O2 (g) –> 2 Al2O3 (s)
Si (s) + O2 (g) –> SiO2 (s)
P4 (s) + 5 O2 –> P4O10 (s)
sulfur forms SO2, but SO3 can be produced at higher temperatures with a catalyst
Describe the reactions of Period 3 elements with air
Na: very fast
Mg: very fast
Al: slow (fast if powdered)
Si: slow
p: spontaneously combusts
S: steadily burns
Which period 3 oxides have high melting points and why?
Na2O, Mgo and Al2O3
form giant ionic lattices
have strong attractive forces
large amount of energy required to break bonds
Why does MgO have a higher melting point than Na2O
Mg2+ ion is attracted more strongly to oxygen than Na+ ion
Why does Al2O3 have a lower melting point than MgO
Al3+ ions distort electron cloud of oxygen
means there is some covalent character, as well as the expected ionic bonds
hence less energy is required to break bonds
Which non-metal oxide has the highest melting point and why?
Which non-metal oxide has the lowest melting point and why?
SiO2
forms macromolecular (giant covalent) structure
has many strong, covalent bonds
large amount of energy needed to break
P4O10 and SO2
form simple molecular structures
weaker intermolecular forces
less energy required to break
What do ionic oxides form when added to water?
Why?
Give equations
form alkaline solutions when added to water
contain O(2-) ions which accepts protons from water molecules when dissolved in solution
Na2O (s) + H2O –> 2NaOH (aq)
-dissolves readily in water
-forms alkaline solution (pH: 12-14)
MgO (s) + H2O (l) –> Mg(OH)2 (aq)
-dissolves sparingly in water
-hence alkaline solution formed is not as strong (pH: 10-11)
Which period 3 oxides are simple covalent oxides
What do simple covalent oxides form when added to water
Give equations for these
P₄O₁₀ and SO₂
acidic solutions (pH: 0-2)
P₄O₁₀ (s) + 6 H2O (l) –> 4 H₃PO₄ (aq)
pH = 0-2
H₃PO₄ (aq) –> 3H+ (aq) + PO₄ 3- (aq)
SO₂ (g) + H2O (l) –> H₂SO₃ (aq)
pH = 2-3
H₂SO₃ (aq) –> 2H+ (aq) + SO₃ 2- (aq)
SO₃ (g) + H2O (l) –> H₂SO₄ (aq)
pH = 0-1
H₂SO₄ (aq)–>2H+ (aq) + SO₄ 2- (aq)
the acids formed dissociate in solution forming H+ and negative ions (aka conjugate bases)
Describe how silicon dioxide and aluminium oxide behave to other oxides added in water
Silicon dioxide
-giant covalent structure = many strong covalent bonds
-large amounts of energy needed to break
-water cannot supply enough energy to break lattice
-hydration enthalpy < bond enthalpy
-hence insoluble in water
-classed as an acid, as it reacts with a base to form a salt
Aluminium oxide:
-has both ionic and covalent character
-insoluble in water
-amphoteric (reacts with both acids and bases to form salts)
Reactions of basic oxides with acids (including equations)
2 HCl (aq0 + MgO (s) → MgCl2 (aq) + H2O (l)
H2SO4 (aq) + Na2O (s) → Na₂SO₄ (aq) + H₂O (l)
Reactions of acidic oxides with bases (including equations)
SiO₂ (s) + 2 NaOH (aq) →Na₂SiO₃ (aq) + H₂O (l)
P₄O₁₀ (s) + 12 NaOH (aq) → 4 Na3PO₄ (aq) + 6H₂O (l)
SO2 + NaOH → Na₂SO3 (aq) + H₂O (l)
SO₃ + NaOH → Na₂SO₄ + H₂O
Reactions involving amphoteric oxides
Al₂O₃ (s) + 2NaOH (aq) + 3H₂O (l) → 2Na[Al(OH)₄] (aq)
Al₂O₃ + H₂SO₄ → Al₂(SO₄)₃ + H₂O
Observation in reaction between sodium and oxygen
White solid and orange flame
Observation in reaction between magnesium and oxygen
White solid and white flame
Observation in reaction between aluminium and oxygen
White solid and white sparkles
Observation in reaction between silicon and oxygen
Burns brilliantly and white solid forms
Observation in reaction between phosphorus and oxygen
White or pink-white flame and white clouds of smoke
Observation in reaction between sulfur and oxygen
Blue flame
Why is the melting point of sulfur (IV) oxide lower than that of phosphorus (V) oxide?
-sulfur (IV) oxide is smaller
-has weaker VDW forces between molecules
-less energy is needed to separate molecules
Explain why SiO2 is classified as an acidic oxide
It reacts with a base
SiO2 + 2NaOH —> Na2SiO3 + H2O
Outline a simple experiment to demonstrate the type of bonding that magnesium oxide gas
-melt it
-molten oxides conduct electricity
-proves it has ionic bonding
