Ch 11 Alkali Metals

THE GROUP 1 ELEMENTS:THE ALKALI METALS

http://kimia.unp.ac.id

Read in the name your God who created Inorganic Chemistry 3

Jurusan KimiaChemistry Department

2

Intro

alkali metal cations are extremely difcult to reducemetal

Davy (British) electrolyzed KOH(l) to extract therst of the alkali metals.

Perey (French), isolated the one alkali metal thatexists only as radioactive isotopes, francium


alkali metal cations are extremely difcult to reducemetal

Davy (British) electrolyzed KOH(l) to extract therst of the alkali metals.

Perey (French), isolated the one alkali metal thatexists only as radioactive isotopes, francium

3

All of the alkali metals :- shiny, silver-colored metals.- high electrical and thermal conductivities.

But, they are also very atypical :Ex: the alkali metals are very soft, and they become softer

as one progresses down the group :Thus, Li can be cut with a knife, whereasK can be squashed like soft butter.

Group Trends


All of the alkali metals :- shiny, silver-colored metals.- high electrical and thermal conductivities.

But, they are also very atypical :Ex: the alkali metals are very soft, and they become softer

as one progresses down the group :Thus, Li can be cut with a knife, whereasK can be squashed like soft butter.

Low m.pLow mp and soft is due to :- Weak metalic bonding- Small enthalpy of atomization

For typical metals, Hatomization = 400 - 600kJ/mol


High thermal conductivity and low m.p of Na heat transfer material in nuclear reactors

For typical metals, Hatomization = 400 - 600kJ/mol

Low mp and soft is due to :- Weak metalic bonding- Small enthalpy of atomization(for typical metals, Hatomization = 400 -600 kJ/mol)

( most metals densities = 5 15 g/cm3)


( most metals densities = 5 15 g/cm3)

water density!

No!reactive with

water

exposed to air a thick coating of oxidationproducts covers the lustrous surface very rapidly :

-react with most nonmetals :

Must be stored under oil


white smoke- dramatic reaction with water supermetals

Feature of alkali metal compounds

Stabilization of Large AnionsCations of the alkali metals (except Li+) :

the largest sizes lowest charge densities, stabilize large low-charge anions.

All are metals have common features.Ions ox.nu = +1,compounds : stable, ionic solids, colorless (without colored anion CrO4-, MnO4-)


8

Stabilization of Large AnionsCations of the alkali metals (except Li+) :

the largest sizes lowest charge densities, stabilize large low-charge anions.

Ion HydrationAll ions are hydrated when dissolved in water.However, this is not always true in the solid phase.Hydration in the crystalline solid balance of lattice energy (U) andHhydration of ionsU = electrostatic attraction between the cations and anions:ion c.d U .


All ions are hydrated when dissolved in water.However, this is not always true in the solid phase.Hydration in the crystalline solid balance of lattice energy (U) andHhydration of ionsU = electrostatic attraction between the cations and anions:ion c.d U .U favors the loss of an ions hydration sphere on crystallization to give thesmall (U ) anhydrous ion.But Hhydration depends on the attraction between the ion and thesurrounding polar water molecules.A major factor contributing to the strength of the ion-dipole attraction is thecharge density of the ions.In this ionic tug-of-war, we nd that high charge density usually favorsretention of all or part of the hydration sphere in thesolid phase, while salts of low-charge ions tend to be anhydrous.

Ion HydrationLow charge densities (compared to other metals).majority of solid alkali metal salts are anhydrous !

c.D of Li+ & Na+ are high enough toform of a few hidrated salts : LiOH.8H2O.


c.D of Li+ & Na+ are high enough toform of a few hidrated salts : LiOH.8H2O.The lowest c.d of all metals,very few K, Rb and Cs salts are hydrated

The low c.d are reflected inthe trend in Hhidration amongthe alkali metalsMg2+ = 1920 kJ/mol

Flame Colors characteristic flame color of alkali metal salt in a flame.


Solubility of alkali metal saltsso useful as reagents in the laboratory of the required anions.

Fact,why ?


1. H ( U and Hhydration of the cation and anion)2. S

soluble, G0 < 0Where, G0=H0 - TS0

Solubility

Fact,why ?

Solubility1. H (the lattice energy and the enthalpy of hydration of the cation and anion)2. S


soluble, G0 < 0Where, G0=H0 - TS0

The lattice energyand hydrationenthalpy terms areessentially equal.



Amazing...

very different in sizesmore soluble

Solubility vs M+ a smooth curve.


very different in sizesmore soluble

Although there is a strong dependence oflattice energy on ionic charge, there is asecondary relationship to the cation/anionradius ratio;mismatch in ionic sizes will leadto a lower than expected lattice energy.

Lithium

the least dense metal (0.53 g.cm ) bright silvery, but turning black if exposed to moist air :

react with dinitrogen(due to the greatest Li charge density of the group)

Li (l) is the most corrosive material known

the most negative Eo of any element releases more energy than any other element when it is oxidized.

Li (aq) + e Li(s) E = -3.05Jurusan KimiaChemistry Department

the least dense metal (0.53 g.cm ) bright silvery, but turning black if exposed to moist air :

react with dinitrogen(due to the greatest Li charge density of the group)

Li (l) is the most corrosive material known

the most negative Eo of any element releases more energy than any other element when it is oxidized.

Li (aq) + e Li(s) E = -3.05density (gcm-3):Lithium = 0.53Al = 67,5Iron = 7.874 gcm3Iridium = 22.65

density (gcm-3):Lithium = 0.53Al = 67,5Iron = 7.874 gcm3Iridium = 22.65

Uses of Lithium

- Aerospace alloyDensity of alloy LA 141(14%Li,1%Al, 85%Mg)=1.35 g/cm3 (=1/2 Aldensity )

- lithium greases-in automotive greases.lithium stearate, CHCOOLi,(Water resistant, not harden at cold, stable at high T ).

Extensive organometallic chemistry of Li


- Aerospace alloyDensity of alloy LA 141(14%Li,1%Al, 85%Mg)=1.35 g/cm3 (=1/2 Aldensity )

- lithium greases-in automotive greases.lithium stearate, CHCOOLi,(Water resistant, not harden at cold, stable at high T ).

Extensive organometallic chemistry of Li

density (gcm-3):Lithium = 0.53Al = 67,5Iron = 7.874Iridium = 22.65

density (gcm-3):Lithium = 0.53Al = 67,5Iron = 7.874Iridium = 22.65

Mobil

Lithium batteries

As anode material: Eo >>> Low density (1/20 of Pb)

mass saving. very low mass per unit of

stored energy compact high-voltage cells.


As anode material: Eo >>> Low density (1/20 of Pb)

mass saving. very low mass per unit of

stored energy compact high-voltage cells.

Lithium-ion Batteries


20

Sodium

1. Extraction of other metal (Th, Zr, tantalum and Ti.ex : TiCl(l) + 4Na(s) Ti(s) + 4 NaCl(s)

2. The production of the gasoline additivetetraethyllead (TEL).

4NaPb(s) + 2CHCl(g) (CH)Pb(l) + 3 Pb(s) + 4NaCl(s)

Uses Of Sodium


1. Extraction of other metal (Th, Zr, tantalum and Ti.ex : TiCl(l) + 4Na(s) Ti(s) + 4 NaCl(s)

2. The production of the gasoline additivetetraethyllead (TEL).

4NaPb(s) + 2CHCl(g) (CH)Pb(l) + 3 Pb(s) + 4NaCl(s)alloy

The Industrial Extraction of Sodium


Potassium

K in the environment is a bitradioactive (0.012% isotop K-40radioactive).

human body radiation

K-40 / Ar-40 is one way of datingrocks


K in the environment is a bitradioactive (0.012% isotop K-40radioactive).

human body radiation

K-40 / Ar-40 is one way of datingrocks

Insoluble Potassium Compounds

The least soluble : the greatest similarity in ion size. very large anion would form the least soluble salts with the large

cations of group 1.

The salts of very large [Co(NO)]with :Li and Na : soluble,

K, Rb, Cs : insoluble.


The least soluble : the greatest similarity in ion size. very large anion would form the least soluble salts with the large

cations of group 1.

The salts of very large [Co(NO)]with :Li and Na : soluble,

K, Rb, Cs : insoluble.

Test of Na+ or K+ in solution :

yellow

The industrial Extraction of Potassium

Electrolysis would be hazardous because of the extremereactivity of the metal.

So, chemical process: (at 850C) :Na(l) + KCl(l) K(g) + NaCl(l)


Electrolysis would be hazardous because of the extremereactivity of the metal.

So, chemical process: (at 850C) :Na(l) + KCl(l) K(g) + NaCl(l)

Le Chtelier to get more K gas

OXIDES

Of the alkali metals, only Li forms a normal oxide :4Li(S) + O(g) 2LiO(s)

NaO (sodium peroxide),containing the dioxide (2-) ion, O (=peroxide ion)

2Na(s) + O(g) NaO(s) The other three alkali metals react with an excess of O2 to form

dioxides(1-) (traditionally named superoxides) :


Of the alkali metals, only Li forms a normal oxide :4Li(S) + O(g) 2LiO(s)

NaO (sodium peroxide),containing the dioxide (2-) ion, O (=peroxide ion)

2Na(s) + O(g) NaO(s) The other three alkali metals react with an excess of O2 to form

dioxides(1-) (traditionally named superoxides) :

HYDROXIDES

The solid hydroxide are white, translucent solids that absorbmoisture from the air until they dissolve in the excess water-a processknown as deliquescence.

Alkali metal hydroxides are all extremely hazardous because thehydroxides ion reacts with skin protein to destroy the skin surface.


The Industrial Synthesis of Sodium Hydroxide

electrolysis of brine (aqueous sodium chloride).

2HO(l) + 2e H(g) + 2OH(aq)2Cl(aq) Cl(g) + 2e


The diaphragm cell

Commercial Uses of Sodium Hydroxide

1. Reagent in organic chemical plants,2. Synthesis of other inorganic chemical.3. pulp and paper industry,4. 30 percent is used in hundreds of other ways.


SODIUM CHLORIDE

Seawater is NaCl 3% solution, table salts by using theSuns energy to evaporate seawater

Salt was one of the earliest commodities to be traded


Seawater is NaCl 3% solution, table salts by using theSuns energy to evaporate seawater

Salt was one of the earliest commodities to be traded

Potassium chloride

KCl is recovered from ancientdried lake deposits,the deposits also contain NaCl,KMgCl3.6H2O; MgSO4.H2O; andmany other salts.


31

differences in solubility

adding the mixture of crystals to saturated brine

Separation The Components


adding the mixture of crystals to saturated brine

electrostatic process

32

potassium chloride isused as fertilizer.

Potassium ion is essential element forplant growth and about 4.5 x 107tonnes of potassium chloride are usedworldwide for this purpose every year,so it is a major chemical product.


33

Potassium ion is essential element forplant growth and about 4.5 x 107tonnes of potassium chloride are usedworldwide for this purpose every year,so it is a major chemical product.

Sodium CarbonateIn North America, sodium carbonate isobtained from the mineral trona,Na2CO3.NaHCO3.2H2O(sodiumsesquicarbonate). Sesqui meansone and one-half, and it is the numberof sodium ions per carbonate unit in themineral. In the monohydrate process

of extraction, trona is minedabout 400 m underground,crushed, and then heated(calcined) in rotary kilns.


34

In the monohydrate processof extraction, trona is minedabout 400 m underground,crushed, and then heated(calcined) in rotary kilns.

Sodium carbonate is made by theSolvay, or ammonia-soda, process.This process involves the reactionof sodium chloride with calciumcarbonate:

- used in glass manufacture.the sodium carbonate isreacted with silicon dioxide(sand) and other componentsat about 1500C.

- used to remove alkaline earthmetal ions from watersuppliesby converting them to theirinsoluble carbonates, aprocess called watersoftening.

Uses of Sodium Carbonate


35

- used to remove alkaline earthmetal ions from watersuppliesby converting them to theirinsoluble carbonates, aprocess called watersoftening.

Sodium Hydrogen Carbonate

Sodium hydrogen carbonate is less water-soluble than sodium carbonate.Thus, it can be prepared by bubbling carbondioxide through a saturated solution of thecarbonate:


36

Heating sodiumhydrogen carbonatecauses it todecompose back tosodium carbonate:

The main use is in the food industry (bakingpowder) , to cause bakery products to rise.


37

Ammonia Reaction

The alkali metals themselves have theunusual property of dissolving in liquidammonia to yield solutions that aredeep blue when dilute

When concentrated by evaporation, the solutionshave a bronze color and behave like a liquidmetal. presence of a transition metal catalyst,the solutions decompose to yield the amide salt,NaNH2, and hydrogen gas:


38

When concentrated by evaporation, the solutionshave a bronze color and behave like a liquidmetal. presence of a transition metal catalyst,the solutions decompose to yield the amide salt,NaNH2, and hydrogen gas:

Ammonium Ion asPseudo-Alkali-Metal Ion

A polyatomic ion whose behavior in many ways mimics thatof an ion of an element or of a group of elements.

ammonium ion is a polyatomic cation containing twononmetals, it behaves in many respects like an alkalimetal ion.


39

ammonium ion is a polyatomic cation containing twononmetals, it behaves in many respects like an alkalimetal ion.

The ammonium ion resembles an alkali metal ion in itsprecipitation reactions.

Biological Aspect

The alkali metal ions

-balance the negative chargeassociated with many of theprotein units in the body.

-help to maintain the osmoticpressure within cells, preventingthem from collapsing.


40

The alkali metal ions

-balance the negative chargeassociated with many of theprotein units in the body.

-help to maintain the osmoticpressure within cells, preventingthem from collapsing.

The potential difference underlies many basic processes,- the hearts generation of rhythmic electrical signals- the kidneys unceasing separation of vital and toxic solutes in the blood,- the eyes precise control of the lenss refractive index.

Cells pump sodium ions out of thecytoplasm and pump potassium ions in. It isthis difference in total alkali metal ionconcentrations inside and outside cells thatproduces an electrical potential across thecell membrane.


41

The potential difference underlies many basic processes,- the hearts generation of rhythmic electrical signals- the kidneys unceasing separation of vital and toxic solutes in the blood,- the eyes precise control of the lenss refractive index.

ElementReactionflowcharts


ElementReactionflowcharts

42

Ch 11 Alkali Metals

Documents

Transcript of Ch 11 Alkali Metals