A2 - Periodicity Flashcards
What is Periodicity?
The repeating patterns / trends of physical or chemical properties or reactions.
Reaction of Sodium with cold water What pH?
- vigorous reaction - floats on surface pH of 12-14
Equation for reaction of Sodium with cold water
2Na (s) + 2H2O (l) —> 2NaOH (aq) + H2 (g)
Reaction and equation of Magnesium with Cold water. Give pH value
- very slow - partially soluble pH of 9/10 Mg (s) + 2H2O (l) —> Mg(OH)2 (aq) + H2 (g)
Reaction and equation of Magnesium with Hot water (steam). Give observation.
- faster reaction - white solid formed Mg (s) + H2O (g) —> MgO (s) + H2 (g)
Why is the solution produced from when magnesium reacts with cold water weakly alkaline?
- Magnesium is not very soluble in water as its lattice is stronger
- it’s sparingly soluble so few hydroxide ions are produced
When Period 3 elements react with oxygen, what do they form?
Oxides
Are group 1 ions more acidic or alkali?
More alkali because they are very soluble in aqueous solution so release more OH- ions so are more alkali
Reactions with Oxygen
State which Period 3 element isn’t oxidised to their highest oxidation state & state its oxidation state
- Sulfur forms SO2
- Which has a +4 oxidation state
When Period 3 elements react with oxygen, they are usually oxidised to their _____ oxidation states, same as their _____ _____
When Period 3 elements react with oxygen, they are usually oxidised to their highest oxidation states, same as their group numbers
Reactions with Oxygen
Explain why sulfur isn’t oxidised to its highest oxidation state
A high temperature and catalyst is needed to make SO3, where sulfur has an oxidation state of +6
Reactions with oxygen
Sodium and oxygen
4Na (s) + O2 (g) —-> 2Na2O (s)
White solid of Na2O
Reactions with oxygen
Magnesium and oxygen
2Mg (s) + O2 (g) —-> 2MgO (s)
White solid of MgO
Reactions with oxygen
Aluminium and oxygen
2Al (s) + 1.5O2 (g) —> Al2O3 (s)
White solid of Al2O3
Reactions with oxygen
Silicon and oxygen
Si + O2 (g) —> SiO2 (s)
Sand
Reactions with oxygen
Phosphorus and oxygen
P4 (s) + 5O2 (g) —> P4O10 (g)
White solid of P4O10
Reactions with oxygen
Sulfur and oxygen
S (s) + O2 (g) —> SO2 (g)
Reactions with oxygen
Sulfur dioxide and oxygen
SO2 (g) + 1/2O2 (g) —> SO3 (g)
More ____ metals (Na, Mg) and _____ (P, S) react readily in air, while ___ and ___ react slowly
More reactive metals (Na, Mg) and non-metals (P, S) react readily in air, while Al and Si react slowly
Explain why Na2O, MgO & Al2O3 have high melting points
- Giant ionic lattices
- Strong forces of attraction between ions = lots of energy needed to break bonds
Why does MgO have a higher melting point than Na2O?
- Mg forms 2+ ions
- So bonds more strongly than 1+ Na ions in Na2O
Why does Al2O3 have a lower melting point than MgO?
- ∵ of difference in electronegativity between Al and O isn’t as large as between Mg and O
- Means oxygen ions in Al2O3 don’t attract electrons in metal-oxygen bond as strongly MgO
- Makes bonds in Al2O3 partially covalent
Why does P4O10 and SO2 have low melting points?
- ∵ form simple molecular structure
- Have weak intermolecular forces (dipole-dipole and van der Waals)
- Take little energy to break
Why does SiO2 have a higher melting point than non-metal oxides
- ∵ has giant macromolecular structure
- Have to break strong covalent bonds = lots of energy
Graph of melting points of period 3 oxides
What do ionic compounds exert?
- Non-directional electrostatic attraction forces
- Size of ion decreases across period so can pack more O2- ions around aluminium ion than sodium ion as it is non-directional
Ionic oxides are
Alkaline
Covalent oxides are
Acidic
Explain why covalent oxides (e.g. oxides of phosphorus and sulfur) are acidic
They dissociate in solution forming hydrogen ions and negative ion (called conjugate base)
Explain why ionic oxides are alkaline
- Ionic oxides (of Na and Mg) contain oxide ions (O2-)
- When they dissolve in water, O2- ions accept protons from water molecules to form hydroxide ions
What are the 2 assumptions the perfect ionic model is based on:
- Bonding in compounds is 100% ionic
- Ions are regarded as point charges or perfect spheres and are not distorted
100% Non polar covalent drawing
Polar covalent drawing
100% ionic
Ionic with covalent character drawing
Describe the meanings of values in tables in relation to the perfect ionic model
- If there is no/ little value differences then it is ionic
- If there is a difference and the larger the difference means the greater the covalent character
Simple covalent oxides of non-metals phosphorus and sulfur form acidic solutions that are ___ so the pH is around ___
Simple covalent oxides of non-metals phosphorus and sulfur form acidic solutions that are strong so the pH is around 0-2 (for at least 1 mol dm-3)
Reactions of oxides with water
Sodium oxide and water and give the pH of the product
Na2O (s) + H2O (l) —> 2NaOH (aq)
pH 13/14
Reactions of oxides with water
Magnesium oxide and water and give the pH of the product
MgO (s) + H2O (l) —> Mg(OH)2 (aq)
pH 10/12
Reactions of oxides with water
Aluminium oxide and water
No reaction
Reactions of oxides with water
Silicon dioxide and water
No reaction
Reactions of oxides with water
Phosphorus oxide and water and give pH of the product
P4O10 (s) + 6H2O (l) —> 4H3PO4 (aq)
pH 0/1
Reactions of oxides and water
Sulfur dioxide and water and give the pH of the product
SO2 (g) + H2O (l) —> H2SO3
pH 3
Reactions of oxides with water
Sulfur trioxide and water and give the pH of the product
SO3 + H2O —> H2SO4
pH -1/+1
Phosphoric acid drawing
Can draw the H next to O
Phosphate ion drawing
What happens in the reactions of acids with bases?
Give the word equation
Metal oxides are bases so will react with acids and non-metal oxides
- Metal oxide + acid —-> salt + water
Reactions of acids and bases
Sodium oxide and hydrochloric acid equation
Na2O (s) + 2HCl (aq) —> 2NaCl (aq) + H2O (l)
Reactions of acids and bases
Magnesium Oxide and nitric acid
MgO (s) + 2HNO3 (aq) —> Mg(NO3)2 (aq) + H2O (l)
Reactions with acids and bases
Sodium oxide and sulfuric acid
Na2O (s) + H2SO4 (aq) —> Na2SO4 (aq) + H2O (l)
What symbol would NO3- ions have and why?
They are all soluble in water so would have aqueous symbol
Non metal oxide reactions
Sodium oxide and phosphorus oxide
6Na2O (s) + P4O10 (s) —> 4Na3PO4 (s)
Non metal oxide reactions
magnesium oxide and phosphorus oxide
6MgO (s) + P4O10 (s) —> 2Mg3(PO4)2 (s)
Non metal oxide reactions word equation
Non metal basic + non-metal acidic —> salt
(In the absence of water)
What are amphoteric oxides
They can react with both acids and bases
Amphoteric oxides
Aluminuim oxide + hydrochloric acid
Al2O3 (s) + 6HCl (aq) —> 2AlCl3 (aq) + 3H2O (l)
Amphoteric oxides
aluminium oxide and sulfuric acid
Al2O3 (s) + 3H2SO4 (aq) —> Al2(SO4)3 (aq) + 3H2O (l)
Ionic equation Aluminium oxide with hydrochloric acid or sulfuric acid
Al2O3 (s) + 6H+ (aq) —> 2Al3+ (aq) + 3H2O (l)
Amphoteric oxides
Aluminium oxide + sodium hydroxide + water
Al2O3 (s) + 2NaOH + 3H2O —> 2NaAl(OH)4
Non-metal oxides react with bases give the word equation
Acidic non-metal oxide + base —> salt + water
Non-metal oxides react with bases
Silicon dioxide and sodium hydroxide
SiO2 + 2NaOH (aq) —> Na2SiO3 + H2O
Non-metal oxides react with bases
Phosphorus oxide and sodium hydroxide
P4O10 (s) + 12NaOH (aq) —> 4Na3PO4 + 6H2O
Non-metal oxides react with bases
Sulfur dioxide and sodium hydroxide
SO2 (g) + 2NaOH (aq) —> Na2SO3 + H2O
Non metal oxides react with bases
Sulfur trioxide + sodium hydroxide
SO3 + 2NaOH —> Na2SO4 (aq) + H2O
What colour does universal indicator go for non-metal oxides?
Red e.g. SiO2
What colour does universal indicator go for metal oxides?
Blue / purple
