TÌM HIỂU VỀ NHÓM IA VÀ IIA TRONG BẢNG HỆ THỐNG TUẦN HOÀN

Modern chemical knowledge is based largely on principles that answer the “why” as well as the “howto.”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 sblock elements are somewhat unusual cases, although not all for the same reason.Hydrogen is the simplest element, with one proton and one electron, and its behavior is rather special.Helium lies in the sblock 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.

TÀI LIỆU THAM KHẢO

1 Hóa học vô cơ – Lê Mậu Quyền

2 Bài tập hóa học vô cơ – Lê Mậu Quyền

3 Hóa học vô cơ – Tập 1, 2, 3 – Hoàng Nhâm

4 Hóa học vô cơ – Tập 1, 2 – Nguyễn Thế Ngôn, Trần Thị Đà

5 Cơ sở lý thuyết hóa học – Phần I: Cấu tạo chất – Nguyễn Đình Chi

6 Modern Inorganic Chemistry – W L Jolly

7 Structural Inorganic Chemistry – A F Wells

8 Shriver, Atkins, Inorganic Chemistry (3rd ed, 1999)

W.H Freeman and Company (Chs 2, 18 )

9 A.R West, Basic Solid State Chemistry (2nd ed 1999)

Wiley, New York, 1999

10.C N R Rao, University General Chemistry (18nd 2006), MACMILLAN

THE S-BLOCK ELEMENTS

• 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 one electron, 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.

GROUP IA: THE ALKALI METALS

Spodumene LiAl(SiO3)2

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.

Flame Colors

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 and potassium).

• 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.

Diagonal Relationships:The Special Case of Lithium

In some of its properties, lithium and its

compounds resemble magnesium and its

compounds

– Lithium carbonate, fluoride, hydroxide, and phosphate 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 hydroxide decompose to form the oxide on heating, while the carbonates and hydroxides of other Group 1A metals are thermally stable.

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—

• 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 KO 2 , 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 2 2 3 2 3 2 2

Na O + KO + CO  → Na CO + K CO + O Z

feedstock for other chemicals

– KCl from natural brines

– Plant fertilizers, feedstock.

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 in submarines 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

– Currently mined from rich U.S resources but can be manufactured by the

Solvay process (E Solvay, Belgium, 1838-1922).

Production and Use

Preparation of Sodium Compounds from NaCl

The methods of preparation suggested by this diagram are not

necessarily the preferred industrial methods.

The Solvay Process—One Way

to Diagram an Industrial Process

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 the atoms

• Sodium ions are found primarily in fluids outside cells and potassium ions are abundant in fluids within cells

• Because most alkali metal compounds are

water soluble, many drugs that are weak acids are administered in the form of their sodium or potassium salts

• Lithium carbonate is used in medicine to level out the dangerous manic “highs” that occur in manic-depressive psychoses

Oxides and Hydroxides

• Reaction with oxygen produces several ionic 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.

Soaps and Detergents

• A soap acts by dispersing (phân tán)grease and oil films into microscopic droplets

• The droplets detach(tách) themselves from the surfaces being cleaned, become suspended in water, and are removed by rinsing

• The alkali metal soaps are water soluble; the

alkaline earth metal soaps are not

• A soap can function well in hard water only

after a part of it is used up to precipitate (kết

tủa)all the alkaline earth metal ions present; in

other words, the soap softens the water first.

Detergents and Soaps

Cleaning Action of a Soap

A 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.

GROUP 2: THE ALKALINE EARTH METALS

Emerald is based on

the mineral beryl:

• 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).

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 does group 1A.

• The higher densities of the group 2A metals are mainly

a consequence(kết quả) 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 in strength 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

1 Là kim loại hoạt động, tăng dần từ BeRa Kém

so với KL kiềm do Z lớn, r nhỏ hơn

2 Dễ mất 2e trở thành M 2+ 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

These were named alkaline earths because of their

intermediate nature between the alkalis (oxides of the alkali metals) and the rare earths ( oxides of rare earth metals).

The alkaline earth metals are silvery colored, soft,

low-density metals , which react readily with halogens to

form ionic salts, and with water, though not as rapidly as the alkali metals, to form strongly alkaline (basic) hydroxides For example, where sodium and potassium react with water at room temperature, magnesium reacts only with steam and calcium with hot water.

Mg + 2H 2 O → Mg(OH) 2 + H 2 Beryllium is an exception: It does not react with water or

steam, and its halides are covalent.

Reactions of Group 2A Metals

• Reactivity with water increases from beryllium

– 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:

• 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

• Unreactive toward air and water

• BeO does not react with water, all others from hydroxides

• Be and BeO dissolve in strongly basic

solutions to form the BeO22- ion (therefore

are acidic).

• BeCl2 and BeF2 melts are poor conductors:

– Therefore they are covalent rather than ionic solids.

The Special Case of Beryllium

• Beryllium is somewhat different from the rest of

• Molten(nấu chảy) BeF2 and BeCl2 are poor

conductors of electricity; they are molecular

substances (see below) The other group IIA

compounds are almost entirely ionic.

Beryllium Chloride

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(bê tông).

• Ordinary soda–lime (Na + Ca)glass is formed by heating limestone, sand, and sodium carbonate together.

Important Compounds of

• Limestone is used in the metallurgy (luyện kim) of

iron and steel to produce an easily liquefied

mixture of calcium silicates called slag(xỉ) , which

carries away impurities from the molten metal.

• Precipitated (kết tủa)( purified) calcium carbonate

is used extensively as a filler in paint, plastics,

printing inks, and rubber.

• It is also used as a mild abrasive (chất mòn nhẹ)

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

• Quicklime (CaO) and slaked lime [Ca(OH)2] are the cheapest 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 has the formula CaSO4 ·½ H2O and is

obtained by heating gypsum

• Gypsum is used to make the familiar “drywall”

or “plaster board” wall material

Decomposition of CaCO3 (lime)

In the lime kiln:

Δ

Stalactites and Stalagmites

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 form Ca(OH)2 which subsequently reacts with CO2 to form CaCO3.

Occurrence, Preparation, Uses, and

Reactions of Group 2A Metals

• Calcium and magnesium rank just ahead of sodium and

potassium in abundance in the Earth’s crust.

• Limestone is mainly CaCO 3 ; dolomite is MgCO 3 · CaCO 3

• 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 mineral

beryl, Be3 Al 2 Si 6 O 18

• Some familiar gemstones, including aquamarine and

emerald, are beryl, distinctively colored by impurities.

• To obtain beryllium metal, beryl is first converted

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 temperature reduction of their oxides, using aluminum as the reducing agent.

high-• Until recently, magnesium was obtained by the

Less expensive methods of obtaining magnesium are now available.

Dow Process for Production of Mg

Electrolysis of Molten MgCl2

• Alloys of beryllium with other metals have many

applications such as springs, clips, and lightweight

• 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

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 Ba 2+ ion is toxic.

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, the somewhat-soluble salt forms CaCO3 again

Deposited CaCO3 leads to stalactites, stalagmites, and other cave formations.

Hard Water and Water Softening

• Hard water is groundwater that contains significant

concentrations of ions (Ca 2+ , Mg 2+ , Fe 2+ ) from natural

sources.

• Hard water tends to precipitate soaps, reducing their effectiveness.

• If the primary anion is the hydrogen carbonate ion

(HCO 3- ), the hardness is said to be temporary

hardness.

• If the primary anions are other than bicarbonate ion

(Cl - , SO 42- , HSO 4- )then the hardness is called

permanent hardness.

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

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 by

precipitating the

multivalent ions using

slaked lime Ca(OH)2

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 Mg 2+ and Ca 2+ of

Palmitic acid

(a common soluble soap).

Water Softening

• Ion exchange.

– Undesirable cations, Mg2+

Ca2+ and Fe3+ are

changed for ions that are

not as undesirable, ex

Na+.

– Resins or zeolites.