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CH10134B > The group 1 elements > Flashcards

The group 1 elements Flashcards

1
Q

What is special about Francium?

A

It is radioactive and has not been isolated as the pure element.

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2
Q

What are some of the physical properties of the group 1 elements?

A

Low melting points, boiling points and enthalpies of atomisation and low densities.

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3
Q

Why are some of the physical properties of the group 1 elements observed?

A

Weak metallic bonding and large atomic radii and relatively open body-centered cubic structures.

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4
Q

How can lithium and sodium metals be obtained?

A

Industrially by electrolysis of their molten chlorides.

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5
Q

Why is CaCl2 added in the electrolysis of sodium?

A

To reduce the melting point.

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6
Q

How are potassium, rubidium and caesium metals prepared?

A

The reduction of their molten salts with sodium at high temperatures.

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7
Q

What is the driving force in the reaction used to prepare potassium/rubidium/caesium metals?

A

They are more reducing than sodium so the equilibrium lies to the left hand side. The element can be obtained by fractional distillation which displaces the equilibrium to the right-hand side.

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8
Q

How do the group 1 metals form oxides?

A

They burn in air - but the major product depends on the metal.

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9
Q

What is the major product of combustion of lithium?

A

Li2O.

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10
Q

What is the major product of combustion of sodium?

A

NA2O2 - peroxide.

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11
Q

What is the major product of combustion of potassium ad heavier metals?

A

Superoxides - MO2.

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12
Q

What is a property of all of the group 1 oxides?

A

They are basic and react with water to give the hydroxides.

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13
Q

Why does the major product of combustion change going down the group?

A

Large anions are stabilised by large cations. Down the group the size of the cation increases and they become better at stabilising the large peroxide and superoxide ions.

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14
Q

What are the class of compounds that form intensely coloured compounds called?

A

Suboxides.

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15
Q

Despite the metal oxidation state appearing to be less than +1, what actually is the case in the suboxides?

A

The additional electrons are delocalised across the whole structure, which give rise to metallic behaviour.

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16
Q

What products do the group 1 elements form with water?

A

The hydroxide and hydrogen gas.

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17
Q

What happens to the reactivity of group 1 with water down the group?

A

It increases.

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18
Q

Which group 1 elements float on water?

A

Lithium, sodium and potassium.

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19
Q

Which group 1 elements sink in water?

A

Rubidium and caesium.

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20
Q

Are the reactions endothermic or exothermic?

A

Exothermic - they can melt the metal (apart from lithium).

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21
Q

How is sodium hydroxide produced industrially?

A

The electrolysis of sodium chloride solution - this is the chloralkali process.

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22
Q

What is the equation for the chloralkali process?

A

2NaCl + 2H2O —> 2NaOH + H2 + Cl2

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23
Q

What are the properties of the group 1 halides?

A

They are colourless ionic solids with high melting points.

24
Q

How can sodium chloride be obtained?

A

Mining naturally occurring deposits or the evaporation of sea water.

25
Q

What is the product of the group 1 metals reacting with ethyne?

A

(In liquid ammonia) they react to form ethynides (also known as acetylides) which contain the HC2- monoanion, or the C22- dianion.

26
Q

Write the equations for the reaction of lithium with ethyne (in the presence of liquid ammonia).

A

2Li + 2HC///CH —-> 2Li+C///CH- + H2

2Li + HC///CH —-> (Li+)2C///C2- + H2

27
Q

What happens when the ethynides are added to water?

A

They decompose to form the hydroxide and ethyne.

28
Q

Give the equation for the decomposition of an ethynide in water.

A

Li2C2 + 2H2O —> 2LiOH + C2H2

29
Q

What is the only group 1 element that forms a stable binary nitride?

A

Lithium.

30
Q

How is the only stable binary nitride formed and give the equation.

A

The reaction of lithium with nitrogen at high temperature and pressure.
6Li + N2 –> 2Li3N

31
Q

What happens when the group 1 nitride is added to water?

A

It decomposes to form lithium hydroxide and ammonia.

32
Q

What salts can group 1 elements form with oxoanions?

A

Nitrates, carbonates and sulfates.

33
Q

What do the nitrates decompose on heating to form?

A

Nitrites (MNO2).

34
Q

What does decomposition of Lithium nitrate give?

A

Lithium oxide, nitrogen monoxide and oxygen.

35
Q

What happens to stability of the nitrates as you go down the group?

A

It increases due to the decrease in the difference between lattice enthalpies of the nitrate and nitrite which makes decomposition less favourable.

36
Q

What happens to compounds with small anions in terms of stability down the group?

A

It generally decreases due to the decrease in lattice enthalpies as the group is descended.

37
Q

What happens to the solubility of group 1 compounds with large anions down the group?

A

The solubility decreases - the lithium salts are the most soluble.

38
Q

What determines how soluble a compound is?

A

The magnitudes of the lattice gibbs energy and gibbs energy changes of hydration of the ions.

39
Q

Is a compound with a small cation and small anion soluble?

A

No.

40
Q

Is a compound with a small cation and large anion soluble?

A

Yes.

41
Q

Is a compound with a large cation and small anion soluble?

A

Yes.

42
Q

Is a compound with a large cation and large anion soluble?

A

No.

43
Q

What can group 1 ions coordinate to?

A

Weakly to simple ligands as they are large and singly charged.

44
Q

What happens to the coordination down the group?

A

It becomes weaker.

45
Q

Who first prepare Crown ethers?

A

Charles Pedersen in the 1960s.

46
Q

What is the optimum spatial fit?

A

The idea that there is a relationship between the cavity size, cationic radius and stability of the resulting complex.

47
Q

What are Crown ethers?

A

Organic compounds whose molecules are large rings containing a number of ether linkages.

48
Q

What is Valinomycin?

A

A naturally occuring marcocyclic antibiotic that is made up from 6 amino acids and 6 hydroxy acids alternating in a ring.

49
Q

What are cryptands?

A

They are more stable complexes than crown ethers as less rearrangement of the ligand is needed to coordinate the cation. They are size selective and form the most stable complexes with cations that fit best into the central cavity.

50
Q

What happens when group 1 metals are dissolved in ammonia?

A

They give dark blue solutions.

51
Q

What happens to the metal ions when they are dissolved in ammonia?

A

They ionise into cations and electrons which are solvated by the liquid ammonia.

52
Q

What causes the colour of the metal-ammonia solution?

A

The solvated electrons.

53
Q

Are the solutions formed from dissolving metal in ammonia reducing or oxidising agents?

A

Strong reducing agents due to the solvated electrons.

54
Q

What happens at high concentrations of the metal?

A

The blue colour turns into a metallic bronze and the solution begins to conduct electricity.

55
Q

What happens after several days of a high concentration dissolved in ammonia?

A

As they are thermodynamically unstable the ammonia is reduced to form sodiu amide and hydrogen.

56
Q

What are some unusual properties of Lithium compared to the other group 1 elements?

A

It is the only element that reacts with N2 to give a nitride, it gives LI2O as the oxide whereas other group 1 metals give peroxides or superoxides, the carbonate and hydroxide decompose on heating to give Li2O whereas the other members are stable to heating, LiNO3 decomposes on heating to form Li2O but the others decompose to form the nitrites and the carbonate, fluoride and hydroxide are far less soluble in water than the other group 1 metals.

57
Q

Why are these strange properties of lithium observed?

A

Due to the expected pattern of changes with a decreasing cation size - there is an increase in lattice enthalpy and gibbs energy changes of hydration - these are key factors in determining the thermal stabilities and solubilities of the group 1 compounds.

CH10134B (16 decks)

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