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THE S -BLOCK ELEMENTS
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Introduction Modern chemical knowledge is based largely on principles
that answer the “why” as well as the “how-to.”
In the remaining chapters, we will emphasize facts and
applications, but we will refer to underlying principles
repeatedly.
Four of the 14 elements that comprise the s -block elements
are somewhat unusual cases, although not all for the same
reason.
Hydrogen is the simplest element, with one proton and oneelectron, and its behavior is rather special.
Helium lies in the s -block but its electron configuration fits with the
noble gases, and it will be considered in the next chapter.
Francium and radium are highly radioactive and we will not
consider them further.
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GROUP IA: THE ALKALI METALS
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Spodumene LiAl(SiO3)2
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The Alkali Metals
Discoveries are recent.
Sodium and potassium (1807) by
electrolysis.
Cesium (1860) and rubidium (1861) from
emission spectra.
Francium (1939) from actinium
radioactive decay.
Most salts are water soluble.
Natural brines are good sources.
Natural deposits allow mining of solids.
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FlameColors
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Properties and Trends in Group 1A
The Group 1A metals exhibit regular trends for a
number of properties.
Irregular trends suggest that factors are working
against each other in determining a property (such as
the density ―discrepancy‖ between sodium andpotassium).
The alkali metals have two notable physical
properties: they are all soft and have low melting
points. When freshly cut, the alkali metals are bright and
shiny—typical metallic properties. The metals quickly
tarnish, however, as they react with oxygen in the air.
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Diagonal Relationships:The Special Case of Lithium
In some of its properties, lithium and its
compounds resemble magnesium and itscompounds.
Lithium carbonate, fluoride, hydroxide, andphosphate are much less water soluble than those
of other alkali metals.
Lithium is the only alkali metal that forms a nitride(Li3N).
When it burns in air, lithium forms a normal oxide(Li2O) rather than a peroxide or a superoxide.
Lithium carbonate and lithium hydroxidedecompose to form the oxide on heating, while the
carbonates and hydroxides of other Group 1Ametals are thermally stable.
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Diagonal
Relationships
The elements in
each encircled
pair haveseveral similar
properties.
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Occurrence, Preparation, Use, & Reactions of the Alkali Metals
Sodium and potassium are isolated primarily from
brines (solutions of NaCl and KCl).
Lithium is obtained mostly from the mineral
spodumene, LiAl(SiO3)2.
To convert an alkali metal ion into an alkali metal
atom, the ion must take on an electron—a process of
reduction.
This is not easy with the alkali metals; they are
excellent reducing agents.
Potassium was the first alkali metal to be prepared by
electrolysis.
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Liquid sodium is used as a heat transfer medium in some
types of nuclear reactors and in automobile engine valves,and its vapor is used in lamps for outdoor lighting.
Potassium is used in making KO2, used as an oxygen
source for miner’s “self -rescuers” and similar devices:
Lithium is used in lightweight batteries of the type
found in heart pacemakers, cellular telephones,
digital cameras, and portable computers.
Occurrence, Preparation, Use, & Reactions of the Alkali Metals
2 2 2 2 2 3 2 3 22 2 2 Na O KO CO Na CO K CO O
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Group I Compounds
Halides
NaCl 50 milliontons/year in U.S.
Preservative, used
on roads, water
softener regeneration,feedstock for other chemicals
KCl from natural brines.
Plant fertilizers, feedstock.
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I C d f
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Important Compounds of
Lithium, Sodium, and Potassium
Lithium carbonate is the usual starting material for
making other lithium compounds:
Li2CO3(aq) + Ca(OH)2(aq) CaCO3(s) + 2 LiOH(aq)
One use of LiOH is to remove CO2 from expired air insubmarines and space vehicles:
2 LiOH(s) + CO2(g) Li2CO3(aq) + H2O
NaCl is the most important industrial sodium
compound (50 million tons/yr).
It is used to prepare a number of other chemicals and
consumer products, including plastics, paper, bleach,
soap, and laundry detergent.
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Carbonates
Li2CO3 is unstable relative to the oxide.Used to treat manic depression (1-2 g/day).
Na2CO3 primarily used to manufacture
glass.
Currently mined from rich U.S. resources but
can be manufactured by the Solvay process
(E. So lvay, Belg ium , 1838-1922) .
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Production and Use
2 NaCl(l) → 2 Na(l) + Cl2(g)
Electrolysis:
KCl(l) + Na(l) → 2 NaCl(l) + K(g)
Sodium as a reducing agent:
TiCl4 + 4 Na → Ti + 4 NaCl
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Preparation of Sodium
Compounds from NaCl
The methods of preparation suggested by this diagram are not
necessarily the preferred industrial methods.
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The Solvay Process—One Way
to Diagram an Industrial Process
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The Alkali Metals and Living Matter
Hydrogen, oxygen, carbon, and nitrogen are the most
abundant elements in the human body, in the order listed.
Sodium and potassium ions are in a second tier of seven elements that account for about 0.9% of theatoms.
Sodium ions are found primarily in fluids outside cellsand potassium ions are abundant in fluids within cells.
Because most alkali metal compounds are water soluble, many drugs that are weak acids areadministered in the form of their sodium or potassiumsalts.
Lithium carbonate is used in medicine to level out thedangerous manic ―highs‖ that occur in manic-
depressive psychoses.
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Sodium Sulfate
H2SO4(conc. aq) + NaCl(s) → NaHSO4(s) + HCl(g)
NaHSO4(s) + NaCl(s) → Na2SO4(s) + HCl(g)
I n the Kraft Process for making paper:
Na2SO4(s) + 4 C(s) → Na2S(s) + 4 CO(g)
45 kg/ton paper
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Oxides and Hydroxides
Reaction with oxygen produces severalionic oxides.
In limited oxygen supplies:
M2O (small amounts of Li2O2 from Li). In excess oxygen:
Li and Na form the peroxide, M2O2.
K, Rb and Cs form the superoxide MO2.
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Soaps and Detergents
A soap acts by dispersing grease and oil filmsinto microscopic droplets.
The droplets detach themselves from the
surfaces being cleaned, become suspended inwater, and are removed by rinsing.
The alkali metal soaps are water soluble; thealkaline earth metal soaps are not.
A soap can function well in hard water only after a part of it is used up to precipitate all thealkaline earth metal ions present; in other
words, the soap softens the water first.
D t t d S
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Detergents and Soaps
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Cleaning Action of a SoapA soap has a
hydrocarbon
“tail” …
… and an
ionic “head”
An oil droplet is
attracted to the
hydrocarbon tails, and
the ionic ends permit
the droplet to be
solubilized in water.
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GROUP 2 THE ALKALINE EARTH METALS
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GROUP 2: THE ALKALINE EARTH METALS
Emerald is based on
the mineral beryl:
3BeO·Al2O3 ·6SiO2
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Principle forms:
carbonates, sulfates and silicates
Oxides and hydroxides only sparingly
soluble.
Basic or ―alkaline‖
Compounds do not decompose on
heating.
Therefore named ―earths‖
Heavier elements compounds are more
reactive and are similar to Group I (also in
other respects).
P i d T d i G 2A
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Properties and Trends in Group 2A Group 2A shows the same general trends of
increasing atomic and ionic sizes and decreasing
ionization energies from top to bottom as doesgroup 1A.
The higher densities of the group 2A metals are
mainly a consequence of the large differences in
atomic sizes. The group 2A metals are all good reducing agents.
Mg(OH)2 is virtually insoluble in water, however …
As the cation size increases from top to bottom on
the periodic table, interionic attractions decrease instrength and the solubilities of the compounds in
water increase.
Ba(OH)2 is sufficiently soluble to be used as a titrant
in acid –base titrations.
ĐẶC ĐIỂM CHUNG
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ĐẶC ĐIỂM CHUNG 1. Là kim loại hoạt động, tăng dần từ BeRa.
Kém so với KL kiềm do Z lớn, r nhỏ hơn 2. Dễ mất 2e trở thành M2+ trong hợp chất và
trong dung dịch
3. Thế điện cực tương đương KL kiềm
4. Thể hơi chỉ bao gồm phân tử 1 nguyên tử
5. Ion không màu; nhiều hợp chất ít tan
6. Be khác nhiều hơn so với Li và các
nguyên tố trong nhóm; Be giống nhiều Al,
Mg giống nhiều Zn
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These were named alkaline earths because of their
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. These were named alkaline earths because of their
intermediate nature between the alkalis (ox ides o f
the alkal i metals) and the rare earths (ox ides o f rare
earth m etals). The alkaline earth metals are si lvery co lored, so ft , low -
densi ty m etals , which react readi ly w ith halogens to
form ionic sal ts , and with water , though not as
rapidly as the alkali metals, to form strongly alkal ine
(basic) hyd rox ides . For example, where sodium and
potassium react with water at room temperature,
magnesium reacts only with steam and calcium with
hot water.
Mg + 2H2O → Mg(OH)2 + H2
Beryllium is an exception: It does not react with water or
steam, and its halides are covalent.
R ti f G 2A M t l
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Reactions of Group 2A Metals Reactivity with water increases from beryllium to
barium: Beryllium does not react with water.
Magnesium reacts with steam but not with cold water.
Calcium reacts slowly with cold water.
Strontium and barium react more rapidly with cold water.
All the alkaline earth metals react with dilute acids to
displace hydrogen:
M(s) + 2 H+
(aq) M2+
(aq) + H2(g). The alkaline earth metals react with the halogens to
form the corresponding halides, with oxygen to form
the oxides, and with nitrogen to form the nitrides.
B lli
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Beryllium
Unreactive toward air and water.
BeO does not react with water, all others
from hydroxides.
Be and BeO dissolve in strongly basicsolutions to form the BeO22- ion (therefore
are acidic ).
BeCl2
and BeF2
melts are poor
conductors:
Therefore they are covalent rather than ionic
solids.
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The Special Case of Beryllium
• Beryllium is somewhat different from the rest of group 2A.• BeO does not react with water, while the other group 2A
metal oxides do so: MO + H2O M(OH)2.
• Be and BeO dissolve in strongly basic solutions to form
the BeO22 – ion. The oxide BeO has acidic properties. The
other alkaline earth metal oxides are basic.
• Molten BeF2 and BeCl2 are poor conductors of electricity;
they are molecular substances (see below). The other
group IIA compounds are almost entirely ionic.
B lli Chl id
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Beryllium Chloride
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Important Compounds of
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Important Compounds of Magnesium and Calcium
Several magnesium compounds occur
naturally, either in mineral form or in brines.
These include the carbonate, chloride,
hydroxide, and sulfate.
Limestone is a naturally occurring form of
calcium carbonate, containing clay and other
impurities.
Portland cement is made by heating limestone,
clay, and sand. When the cement is mixed with
sand, gravel, and water, it solidifies into
concrete.
Important Compounds of
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Important Compounds of
Magnesium and Calcium (cont’d)
Limestone is used in the metallurgy of iron andsteel to produce an easily liquefied mixture of
calcium silicates called slag, which carries away
impurities from the molten metal.
Precipitated (purified) calcium carbonate is usedextensively as a filler in paint, plastics, printing
inks, and rubber.
It is also used as a mild abrasive in toothpastes,food, cosmetics, and antacids.
Added to paper, calcium carbonate makes the
paper bright, opaque, smooth, and capable of
absorbing ink well.
Important Compounds of
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Important Compounds of
Magnesium and Calcium (cont’d)
Quicklime (CaO) and slaked lime [Ca(OH)2] are thecheapest and most widely used bases, and are
usually the first choice for neutralizing unwanted acids.
Slaked lime sees extensive agricultural use.
Quicklime is used to neutralize sulfur oxides formed
when coal burns.
Gypsum has the formula CaSO4·2 H2O. Another
hydrate of calcium sulfate is plaster of paris which hasthe formula CaSO4 ·½ H2O and is obtained by heating
gypsum.
Gypsum is used to make the familiar ―drywall‖ or
―plaster board‖ wall material.
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D iti f C CO (li )
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Decomposition of CaCO3 (lime)
CaO + H2O → Ca(OH)2
slaked lime
In the lime slaker:
CaCO3 → CaO + CO2
burnt lime
or
quicklime
In the lime kiln:
Δ
Stalactites and Stalagmites
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Stalactites and Stalagmites
CO2 + H2O → H3O+ + HCO3
-
K a = 4.410-7
HCO3- + H2O → H3O
+ + CO32-
K a = 4.710-11
CaCO3(s) + H2O(l) + CO2(g) → Ca(HCO3)2(aq)
Oth C d
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Other Compounds
Gypsum, CaSO4·2H2O: Plaster of paris CaSO4·½H2O by heating
bypsum.
Used in drywall. BaSO4 used in X-ray imaging .
Slaked lime used in mortar:
CaO absorbs water from the cement to formCa(OH)2 which subsequently reacts with CO2
to form CaCO3.
Occurrence Preparation Uses and
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Occurrence, Preparation, Uses, and
Reactions of Group 2A Metals
Calcium and magnesium rank just ahead of sodiumand potassium in abundance in the Earth’s crust.
Limestone is mainly CaCO3; dolomite is MgCO3·
CaCO3. Barium and strontium are found in the Earth’s crust at
about 400 ppm, and beryllium is found at 2 ppm.
An important mineral source of beryllium is the mineralberyl , Be3 Al2Si6O18.
Some familiar gemstones, including aquamarine and
emerald, are beryl, distinctively colored by impurities.
To obtain beryllium metal, beryl is first converted to
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y y
BeF2. Then the BeF2 is reduced to beryllium, using
magnesium as the reducing agent.
Calcium is generally obtained by electrolysis of molten
calcium chloride.
Strontium and barium can also be obtained by
electrolysis, but are usually obtained by the high-
temperature reduction of their oxides, using aluminum
as the reducing agent.
Until recently, magnesium was obtained by the
electrolysis of molten MgCl2, in the Dow process. Less
expensive methods of obtaining magnesium are now
available.
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Dow Process for Production of Mg
Electrolysis of Molten MgCl
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Electrolysis of Molten MgCl2
Alloys of beryllium with other metals have many
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y y y
applications such as springs, clips, and lightweight
structural materials.
Beryllium is nonsparking, and tools that must be usedin flammable atmospheres are sometimes made of
beryllium.
Magnesium has a lower density than any other structural metal and is an important metallurgical
reducing agent. Magnesium is also used in batteries
and fireworks.
Calcium is used to reduce the oxides or fluorides of
less common metals to the free metals. Calcium is
also alloyed with lead in lead –acid batteries, and is
used to form other alloys with aluminum and silicon.
The Group 2A Metals
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The Group 2A Metals
and Living Matter
Persons of average size have approximately 25 g of magnesium in their bodies.
The recommended daily intake of magnesium for
adults is 350 mg. Calcium is essential to all living matter. The human
body typically contains from 1 to 1.5 kg of calcium.
Strontium is not essential to living matter, but it is of interest because of its chemical similarity to calcium.
Barium also has no known function in organisms; in
fact, the Ba2+ ion is toxic.
Ch i t f G d t
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Chemistry of Groundwater
Rainwater containing dissolved CO2 is acidic
due to formation of H2CO3.
Acidic rainwater converts CaCO3 to Ca(HCO3)2:
• As the water evaporates from the Ca(HCO3)2, thesomewhat-soluble salt forms CaCO3 again.
Deposited CaCO3 leads to stalactites,
stalagmites, and other cave formations.
Hard Water and Water Softening
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Hard Water and Water Softening Hard water is groundwater that contains
significant concentrations of ions (Ca2+,Mg2+, Fe2+) from natural sources.
Hard water tends to precipitate soaps,
reducing their effectiveness. If the primary anion is the hydrogen
carbonate ion (HCO3-), the hardness is
said to be tempo rary hardness . If the primary anions are other than
bicarbonate ion (Cl-, SO42-, HSO4
-)then the
hardness is called permanent hardness .
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Soft: 0 - 20 mg/L as calcium
Moderately soft: 20 - 40 mg/L as calcium
Slightly hard: 40 - 60 mg/L as calcium
Moderately hard: 60 - 80 mg/L as calcium
Hard: 80 - 120 mg/L as calcium
Very Hard: >120 mg/L as calcium
3 3 2 2( ) M HCO MCO CO H O
Temporary Hard Water
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Temporary Hard Water Contains HCO3
- ion.
When heated gives
CO32-, CO2 and H2O.
The CO32- reacts with
multivalent ions to form
precipitates.(for example CaCO3,
MgCO3)
Soften water byprecipitating the
multivalent ions using
slaked lime Ca(OH)2
Permanent Hard Water
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Permanent Hard Water Contains significant concentrations of
anions other than carbonate.
For example SO42-, HSO4
-.
Usually soften by precipitating the Ca2+ and
Mg2+
using sodium carbonate leaving
sodium salts in solution.
Bathtub ring is caused by
salts of Mg2+ and Ca2+ of
Palmitic acid
(a common soluble soap).
Water Softening
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Water Softening
Ion exchange.
Undesirablecations, Mg2+
Ca2+ and Fe3+
are changed for ions that are
not as
undesirable, ex.Na+.
Resins or
zeolites.
Water SofteningHard water
ith i
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Water Softening
by Ion Exchangewith ions
An ion-exchange
resin with acidic
groups bound to Na+
As hard water passes
through, hard-watercations are
exchanged for Na+
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D i i i
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Deionizing
Instead of replacing cations withNa+, they are replaced with H+.
Then the anions are replaced withOH-.
H+(aq) + OH-(aq) → H2O(l)
Some studies have shown a weak inverse relationship
b t t h d d di l di i
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between water hardness and cardiovascular disease in
men, up to a level of 170 mg calcium carbonate per litre
of water. The World Health Organization has reviewed the
evidence and concluded the data were inadequate toallow for a recommendation for a level of hardness.
A later review by František Kožíšek, M.D., Ph.D. National
Institute of Public Health, Czech Republic gives a good
overview of the topic, and conversely to the WHO, setssome recommendations for the maximum and minimum
levels of calcium (40-80 mg/L) and magnesium (20-30
mg/L) in drinking water, and a total hardness expressed
as the sum of the calcium and magnesium
concentrations of 2-4 mmol/L.
Naturally very soft water is more likely to corrode (i.e. react
chemically with) metal pipes in which it is carried, and as
a result it may have elevated levels of cadmium, copper,
lead and zinc.
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150
2 2
o C Ca H CaH 22 2 Be TiO BeO Ti
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2 2
610 /
22 2o H kJ mol Mg O MgO
3 2 2 2 36 3 ( ) 2Mg N H O Mg OH NH
2 2 2 4
2 2 2 2 2
4 2 ( )
2 ( )
Be C H O Be OH CH
CaC H O Ca OH C H
2 2 2
2 4 2 3 2
2 ( )
( ) 2 2 2
Mg H O Mg OH H
Mg OH NH Cl MgCl NH H O
2 2 4 2
2 2 2
2 2 ( )
2fuse
Be NaOH H O Na Be OH H
Be NaOH Na BeO H
Natri hidroxoberilat
Natri berilat
2 2 BeF Mg Be MgF
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