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