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Inorganic Chemistry > Periodicity 2 > Flashcards

Periodicity 2 Flashcards

1
Q

Describe the physical trends in the elements as you go across period three

A
  • Sodium, magnesium and aluminium are metallic- they are shiny (when freshly exposed to air), conduct electricity and react with dilute acids to give hydrogen and salts.
  • Silicon is a semi-metal (metalloid)- it conducts electricity to some extent, a property that is useful in making semiconductor devices.
  • Phosphorus, sulfur and chlorine are typical non-metals- in particular they do not conduct electricity and have low melting and boiling points.
  • Argon is a noble gas. It is chemically unreactive and exists and different atoms.
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2
Q

Which elements in period three react with water

A
  • Sodium
  • Magnesium
  • Chlorine
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3
Q

Describe the reaction of sodium with water

A
  • The reaction of sodium with water is vigorous
  • The sodium floats on the surface of the water and fizzes rapidly, melting because of the heat energy released by the reaction.
  • A strongly alkaline solution of sodium hydroxide is formed (pH 13-14).
  • H2 gas is also formed
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4
Q

What is the equation for the reaction of sodium with water

A

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

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5
Q

Describe the reaction of magnesium with water

A
  • The reaction is very slow at room temperature.
  • Only a few bubbles of hydrogen are formed after some days.
  • The resulting solution is less alkaline (pH around 10) than in the case of sodium because magnesium hydroxide is only sparingly soluble.
  • The reaction is much faster with heated magnesium and steam and gives magnesium oxide and hydrogen (instead of magnesium hydroxide and hydrogen).
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6
Q

Give the equation for the reaction of magnesium with water at room temperature

A

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

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7
Q

Give the equation for the reaction of heated magnesium and steam

A

Mg (s) + H2O (g) —> MgO (s) + H2 (g)

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8
Q

What elements in period 3 react with oxygen

A

All of them apart from argon

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9
Q

Describe the reaction of sodium with oxygen

A

Sodium burns brightly in air with a characteristic yellow flame to form white sodium oxide.

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10
Q

Give the equation for the reaction of sodium with oxygen

A

2Na (s) + 1/2O2 (g) —> Na2O (s)

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11
Q

Describe the reaction of magnesium with oxygen

A
  • A strip of magnesium ribbon burns in air with a bright white flame.
  • The white powder that is produced is magnesium oxide.
  • If burning magnesium is lowered into a gas jar of oxygen the flame is even more intense.
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12
Q

Give the equation for the reaction of magnesium with oxygen

A

2Mg (s) + O2 (g) —> 2MgO (s)

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13
Q

Describe the reaction of aluminium with oxygen

A
  • When aluminium powder is heated and then lowered into a gas jar of oxygen it burns brightly to give aluminium oxide which is a white powder.
  • Aluminium powder also burns brightly in air.
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14
Q

Give the equation for the reaction of aluminium with oxygen

A

4Al (s) + 3O2 (g) —> 2Al2O3 (s)

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15
Q

Describe the reactivity of aluminium

A
  • Aluminium is a reactive metal but it is always coated with a strongly bonded surface layer of oxide which prevents it from further reaction.
  • This makes aluminium appear and reactive metal and is used for many everyday purposes.
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16
Q

Describe the reaction of silicon with oxygen

A

Silicon with form silicon oxide if it is heated strongly in oxygen

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17
Q

Give the equation for the reaction of silicon with oxygen

A

Si (s) + O2 (g) —> SiO2 (s)

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18
Q

Describe the reaction of phosphorus with oxygen

A
  • Red phosphorus must be heated before it reacts with oxygen.
  • White phosphorus spontaneously ignites in air and the white smoke of phosphorus pentoxide is given off.
  • Red and white phosphorus are allotropes of phosphorus- the same element with atoms arranged differently.
  • If the supply of oxygen is limited, phosphorus trioxide P2O3 is also formed.
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19
Q

Describe the reaction of sulfur with oxygen

A

When sulfur powder is heated and lowered into a gas jar of oxygen, it burns with a blue flame to form the colourless gas sulfur dioxide.

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20
Q

Give the equation for the reaction of sulfur with oxygen

A

S (s) + O2 (g) —> SO2 (g)

21
Q

What is the trend in oxidation numbers of the period three elements in their oxides as you go across the group

A

The oxidation number of the period three element in the oxide increases across the period

22
Q

Describe the properties of the period three metal oxides

A
  • Sodium, magnesium and aluminium oxides form giant ionic lattices.
  • This means they all have high melting points.
  • The bonding in aluminium oxide is ionic but has some covalent character.
23
Q

Explain why the bonding in aluminium oxide has some covalent character

A
  • Aluminium forms a very small ion with a large positive charge and so can approach closely to the O2- and distort its electron cloud.
  • This means that the bond has some covalent character.
24
Q

Explain how to predict the covalent/ionic character of a bond by considering the difference in electronegativities of the two atoms

A

The bigger the difference in electronegativities, the greater the ionic character of the bond.

25
Q

Describe the properties of silicon oxide

A
  • Silicon oxide has a giant covalent (macromolecular) structure.
  • It has a high melting point because many strong covalent bonds must be broken in order to melt it.
26
Q

Describe the properties of phosphorus and sulfur oxides

A
  • Phosphorus and sulfur oxides exist as separate covalently bonded molecules.
  • The phosphorus oxides are solids.
  • Sulfur dioxide and sulfur trioxide are both gases at 298K
  • The intermolecular forces are weak Van Der Waals and dipole-dipole forces.
  • They have relatively low melting points.
27
Q

Describe how sodium oxide reacts with water

A
  • Sodium oxide is a base
  • It reacts with water to give sodium hydroxide which is a strongly alkaline solution with a pH of approximately 14
28
Q

Give the equation for the reaction of sodium oxide with water

A

Na2O (s) + H2O (l) —> 2Na+ (aq) + 2OH- (aq)

29
Q

Describe how magnesium oxide reacts with water

A
  • Magensium oxide is a base
  • It reacts with water to give magnesium hydroxide which is sparingly soluble in water.
  • This produces a somewhat alkaline solution with a pH of approximately 9.
30
Q

Give the equation for the reaction of magnesium oxide with water

A

MgO (s) + H2O (l) —> Mg(OH)2 (s) <=> Mg 2+ (aq) + 2OH- (aq)

31
Q

Which group 3 oxides are insoluble in water

A

Aluminium oxide
Silicon dioxide

32
Q

Which group 3 oxides are acidic oxides

A
  • Phosphorus pentoxide
  • Sulfur dioxide
  • Sulfur trioxide
33
Q

Describe the reaction of phosphorus pentoxide with water

A
  • Phosphorus pentoxide is an acidic oxide.
  • It reacts violently with water to produce an acidic solution of phosphorus (V) acid.
  • This ionises so the solution is acidic.
34
Q

How does phosphoric acid (V) ionise

A

In stages. The first stage is:
H3PO4 (aq) <=> H+ (aq) + H2PO4- (aq)

35
Q

Give the equation for the reaction of phosphorus pentoxide with water

A

P4O10 (s) + 6H2O (l) —> 4H3PO4 (aq)

36
Q

Describe the reaction of sulfur dioxide with water

A
  • Sulfur dioxide is an acidic oxide
  • It is fairly soluble and reacts with water to give an acidic solution of sulfuric (IV) oxide (sulfurous acid).
  • This partially dissociates producing H+ ions which cause the acidity of the solution.
37
Q

Give the equation for the reaction of sulfur dioxide with water

A

SO2 (g) + H2O (l) —> H2SO3 (aq)

38
Q

Give the equation for the partial dissociation of sulfuric (IV) acid (sulfurous acid)

A

H2SO3 (aq) <=> H+ (aq) + HSO3- (aq)

39
Q

Describe the reaction of sulfur trioxide with water

A

Sulfur trioxide reacts violently with water to produce sulfuric acid (sulfur (VI) acid)

40
Q

Give the equation for the reaction of sulfur trioxide with water

A

SO3 (g) + H2O (l) —> H2SO4 (aq)

41
Q

Describe the overall pattern in the reactions of the group 3 oxides as you go across the period

A
  • The metal oxides on the left of the period form alkaline solutions in water.
  • The non-metal oxides on the right of the period form acidic solutions in water.
  • The ones in the middle do not react
42
Q

Explain how the behaviour of the oxides can be understood by looking at their bonding and structure

A
  • Sodium and magnesium oxides are composed of ions.
  • Sodium oxide contains the oxide ion O2- which is a very strong base (it strongly attracts protons) and so readily reacts with water to produce hydroxide ions.
  • This makes the solution strongly alkaline.
  • Magnesium oxide also contains oxide ions.
  • However, its reaction with water produces a less alkaline solution than sodium oxide because it is less soluble than sodium oxide.
  • Aluminium oxide is ionic but the bonding is too strong for the ions to be separated, partly because of the additional covalency it has.
  • Silicon dioxide is a giant macromolecule and water will not affect this type of structure.
  • Phosphorus oxides and sulfur oxides are covalent molecules and react with water to form acid solutions.
43
Q

What is the general trend in the solutions of group 3 oxides across the period

A

Solutions of the oxides of the elements go from alkaline to acidic across the period.

44
Q

Do sodium oxide and magnesium oxide react with acids or bases

A

Sodium oxide and magnesium oxide react with acids to give salt and water only.

45
Q

Does aluminium oxide react with acids or bases

A

Aluminium oxide reacts with both acids and alkalis which makes it an amphoteric oxide

46
Q

Does silicon dioxide react with acids or bases

A

Silicon dioxide will react as a weak acid with strong bases

47
Q

Does phosphorus pentoxide react with acids or bases and describe this reaction

A
  • It reacts with alkalis.
  • The reaction of phosphorus pentoxide with an alkali is really the reaction of phosphoric (V) acid, H3PO4 , because this is formed when phosphorus pentoxide reacts with water.
  • Phosphoric (V) acid has three -OH groups and each of these has an acidic hydrogen atom.
  • So it will react with, for example, sodium hydroxide in three stages.
  • Each hydrogen atom in turn reacts with a hydroxide ion and is replaced by a sodium ion.
48
Q

Does sulfur dioxide react with acids or bases

A

Bases

49
Q

Describe the two reactions that occur when aqueous sulfur dioxide is added to sodium hydroxide

A
  • First sodium hydrogensulfate(IV) is formed NaHSO3
  • Then sodium sulfate (IV) is formed Na2SO3

Inorganic Chemistry (5 decks)

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