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

A2 - Periodicity Flashcards by Jonny Billinton

What is Periodicity?

The repeating patterns / trends of physical or chemical properties or reactions.

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Reaction of Sodium with cold water What pH?

vigorous reaction - floats on surface pH of 12-14

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Equation for reaction of Sodium with cold water

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

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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)

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Reaction and equation of Magnesium with Hot water (steam). Give observation.

faster reaction - white solid formed Mg (s) + H2O (g) —> MgO (s) + H2 (g)

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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

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When Period 3 elements react with oxygen, what do they form?

Oxides

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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

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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

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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

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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

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Reactions with oxygen

Sodium and oxygen

4Na (s) + O₂(g) —-> 2Na₂O (s)

White solid of Na₂O

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Reactions with oxygen

Magnesium and oxygen

2Mg (s) + O₂ (g) —-> 2MgO (s)

White solid of MgO

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Reactions with oxygen

Aluminium and oxygen

2Al (s) + 1.5O₂ (g) —> Al₂O₃(s)

White solid of Al₂O3

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Reactions with oxygen

Silicon and oxygen

Si + O₂(g) —> SiO₂(s)

Sand

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Reactions with oxygen

Phosphorus and oxygen

P4 (s) + 5O₂(g) —> P₄O₁₀(g)

White solid of P₄O₁₀

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Reactions with oxygen

Sulfur and oxygen

S (s) + O₂ (g) —> SO₂(g)

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Reactions with oxygen

Sulfur dioxide and oxygen

SO₂ (g) + 1/2O₂(g) —> SO₃ (g)

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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

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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

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Why does MgO have a higher melting point than Na₂O?

Mg forms 2+ ions
So bonds more strongly than 1+ Na ions in Na₂O

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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

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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

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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

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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 O^2-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 (O^2-) * When they dissolve in water, O^2- ions accept protons from water molecules to form hydroxide ions

What are the 2 assumptions the perfect ionic model is based on:

1. Bonding in compounds is 100% ionic 2. 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 NO_3-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

A2 - Periodicity Flashcards

(64 cards)