GROUP 2: THE ALKALINE EARTH METALS GROUP 2: THE ALKALINE EARTH METALS
Emerald is based on the mineral beryl:
3BeO∙Al2O3 ∙6SiO2
Principle forms: Principle forms: carbonates, sulfates and silicates carbonates, sulfates and silicates Oxides and hydroxides only sparingly Oxides and hydroxides only sparingly soluble. soluble. Basic or “alkaline” Basic or “alkaline” Compounds do not decompose on Compounds do not decompose on heating. heating. Therefore named “earths” Therefore named “earths” Heavier elements compounds are more Heavier elements compounds are more reactive and are similar to Group I (also in reactive and are similar to Group I (also in other respects). other respects).
Properties and Trends in Group 2A Properties and Trends in Group 2A
Ba(OH)
Group 2A shows the same general trends of Group 2A shows the same general trends of increasing atomic and ionic sizes and decreasing increasing atomic and ionic sizes and decreasing ionization energies from top to bottom as does ionization energies from top to bottom as does group 1A. group 1A. The higher densities of the group 2A metals are The higher densities of the group 2A metals are mainly a consequence of the large differences in mainly a consequence of the large differences in atomic sizes. atomic sizes. The group 2A metals are all good reducing agents. The group 2A metals are all good reducing agents. is virtually insoluble in water, however … Mg(OH)22 is virtually insoluble in water, however … Mg(OH) As the cation size increases from top to bottom on As the cation size increases from top to bottom on the periodic table, interionic attractions decrease in the periodic table, interionic attractions decrease in strength and the solubilities of the compounds in strength and the solubilities of the compounds in water increase. water increase. Ba(OH)22 is sufficiently soluble to be used as a titrant is sufficiently soluble to be used as a titrant in acid–base titrations. in acid–base titrations.
ĐẶC ĐIỂM CHUNG 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
. 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 + 2H2O → Mg(OH)2 + H2 Beryllium is an exception: It does not react with water or
steam, and its halides are covalent.
Reactions of Group 2A Metals Reactions of Group 2A Metals Reactivity with water increases from beryllium to Reactivity with water increases from beryllium to barium: barium: Beryllium does not react with water. Beryllium does not react with water. Magnesium reacts with steam but not with cold water. Magnesium reacts with steam but not with cold water. Calcium reacts slowly with cold water. Calcium reacts slowly with cold water. Strontium and barium react more rapidly with cold water. Strontium and barium react more rapidly with cold water. All the alkaline earth metals react with dilute acids to All the alkaline earth metals react with dilute acids to displace hydrogen: displace hydrogen: M(s) + 2 H++(aq) M(s) + 2 H
(aq) M M2+2+(aq) + H
(g). (aq) + H22(g).
The alkaline earth metals react with the halogens to The alkaline earth metals react with the halogens to form the corresponding halides, with oxygen to form form the corresponding halides, with oxygen to form the oxides, and with nitrogen to form the nitrides. the oxides, and with nitrogen to form the nitrides.
Beryllium Beryllium
ion (therefore 2-2- ion (therefore
Unreactive toward air and water. Unreactive toward air and water. BeO does not react with water, all others BeO does not react with water, all others from hydroxides. from hydroxides. Be and BeO dissolve in strongly basic Be and BeO dissolve in strongly basic solutions to form the BeO22 solutions to form the BeO are are acidic
melts are poor and BeF22 melts are poor
acidic).). BeClBeCl22 and BeF conductors: conductors: Therefore they are covalent rather than ionic Therefore they are covalent rather than ionic solids. solids.
The Special Case of Beryllium 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 2– ion. The oxide BeO has acidic properties. The other
BeO2 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.
Beryllium Chloride Beryllium Chloride
Limestone
Portland cement
Ordinary
Important Compounds of Important Compounds of Magnesium and Calcium Magnesium and Calcium Several magnesium compounds occur Several magnesium compounds occur naturally, either in mineral form or in brines. naturally, either in mineral form or in brines. These include the carbonate, chloride, These include the carbonate, chloride, hydroxide, and sulfate. hydroxide, and sulfate. Limestone is a naturally occurring form of is a naturally occurring form of calcium carbonate, containing clay and other calcium carbonate, containing clay and other impurities. impurities. Portland cement is made by heating limestone, clay, is made by heating limestone, clay, and sand. When the cement is mixed with sand, and sand. When the cement is mixed with sand, concrete.. gravel, and water, it solidifies into concrete gravel, and water, it solidifies into soda–lime glass is formed by heating Ordinary soda–lime glass is formed by heating limestone, sand, and sodium carbonate together. limestone, sand, and sodium carbonate together.
(purified) calcium carbonate is used calcium carbonate is used
Important Compounds of Important Compounds of Magnesium and Calcium (cont’d) Magnesium and Calcium (cont’d) Limestone is used in the metallurgy of iron and steel to Limestone is used in the metallurgy of iron and steel to produce an easily liquefied mixture of calcium silicates produce an easily liquefied mixture of calcium silicates slag, which carries away impurities from the which carries away impurities from the called slag, called molten metal. molten metal. Precipitated Precipitated (purified) extensively as a filler in paint, plastics, printing inks, extensively as a filler in paint, plastics, printing inks, and rubber. and rubber. It is also used as a mild abrasive in toothpastes, food, It is also used as a mild abrasive in toothpastes, food, cosmetics, and antacids. cosmetics, and antacids. Added to paper, calcium carbonate makes the paper Added to paper, calcium carbonate makes the paper bright, opaque, smooth, and capable of absorbing ink bright, opaque, smooth, and capable of absorbing ink well.well.
Quicklime (CaO) and slaked lime [Ca(OH)
Important Compounds of Important Compounds of Magnesium and Calcium (cont’d) Magnesium and Calcium (cont’d) Quicklime (CaO) and slaked lime [Ca(OH)22] are the ] are the cheapest and most widely used bases, and are usually the cheapest and most widely used bases, and are usually the first choice for neutralizing unwanted acids. first choice for neutralizing unwanted acids. Slaked lime sees extensive agricultural use. Slaked lime sees extensive agricultural use. Quicklime is used to neutralize sulfur oxides formed when Quicklime is used to neutralize sulfur oxides formed when coal burns. coal burns. O. Another Gypsum has the formula CaSO44·2 H·2 H22O. Another Gypsum has the formula CaSO which has plaster of paris which has hydrate of calcium sulfate is plaster of paris hydrate of calcium sulfate is the formula CaSO4 4 ·½ H·½ H22O and is obtained by heating O and is obtained by heating the formula CaSO gypsum. gypsum. Gypsum is used to make the familiar “drywall” or Gypsum is used to make the familiar “drywall” or “plaster board” wall material. “plaster board” wall material.
(lime) Decomposition of CaCO3 3 (lime) Decomposition of CaCO
In the lime kiln:
Δ →
CaCO3
CaO + CO 2
burnt lime or quicklime
→
In the lime slaker: CaO + H2O
Ca(OH) 2 slaked lime
Stalactites and Stalagmites Stalactites and Stalagmites
CO2 + H2O
H→ 3O+ + HCO3 Ka = 4.4107
HCO3
+ H2O
H→ 3O+ + CO3
2 Ka = 4.71011
→
Ca(HCO
CaCO3(s) + H2O(l) + CO2(g)
3)2(aq)
Other Compounds Other Compounds
Gypsum, CaSO
Gypsum, CaSO44·2H·2H22O:O: Plaster of paris
Plaster of paris CaSOCaSO44·½H·½H22O by heating O by heating bypsum. bypsum. Used in drywall. Used in drywall.
used in X-ray imaging . BaSOBaSO44 used in X-ray imaging . Slaked lime used in mortar: Slaked lime used in mortar: CaO absorbs water from the cement to form CaO absorbs water from the cement to form which subsequently reacts with CO22 Ca(OH)22 which subsequently reacts with CO Ca(OH) to form CaCO33.. to form CaCO
Occurrence, Preparation, Uses, and Occurrence, Preparation, Uses, and Reactions of Group 2A Metals Reactions of Group 2A Metals Calcium and magnesium rank just ahead of sodium Calcium and magnesium rank just ahead of sodium and potassium in abundance in the Earth’s crust. and potassium in abundance in the Earth’s crust.
Limestone is mainly CaCO
; dolomite is MgCO33· ·
Limestone is mainly CaCO33; dolomite is MgCO CaCOCaCO33..
Barium and strontium are found in the Earth’s crust at about Barium and strontium are found in the Earth’s crust at about 400 ppm, and beryllium is found at 2 ppm. 400 ppm, and beryllium is found at 2 ppm.
An important mineral source of beryllium is the mineral An important mineral source of beryllium is the mineral beryl, Be beryl
, Be33AlAl22SiSi66OO1818..
Some familiar gemstones, including aquamarine and Some familiar gemstones, including aquamarine and emerald, are beryl, distinctively colored by impurities. emerald, are beryl, distinctively colored by impurities.
To obtain beryllium metal, beryl is first converted to To obtain beryllium metal, beryl is first converted to is reduced to beryllium, using . Then the BeF22 is reduced to beryllium, using BeFBeF22. Then the BeF magnesium as the reducing agent. magnesium as the reducing agent.
Calcium is generally obtained by electrolysis of molten Calcium is generally obtained by electrolysis of molten calcium chloride. calcium chloride.
Strontium and barium can also be obtained by Strontium and barium can also be obtained by electrolysis, but are usually obtained by the high- electrolysis, but are usually obtained by the high- temperature reduction of their oxides, using aluminum temperature reduction of their oxides, using aluminum as the reducing agent. as the reducing agent.
. Less Dow process. Less
Until recently, magnesium was obtained by the Until recently, magnesium was obtained by the , in the Dow process electrolysis of molten MgCl22, in the electrolysis of molten MgCl expensive methods of obtaining magnesium are now expensive methods of obtaining magnesium are now available. available.
Dow Process for Production of Mg Dow Process for Production of Mg
Electrolysis of Molten MgCl22 Electrolysis of Molten MgCl
Alloys of beryllium with other metals have many Alloys of beryllium with other metals have many applications such as springs, clips, and lightweight applications such as springs, clips, and lightweight structural materials. structural materials.
Beryllium is nonsparking, and tools that must be used Beryllium is nonsparking, and tools that must be used in flammable atmospheres are sometimes made of in flammable atmospheres are sometimes made of beryllium. beryllium.
Magnesium has a lower density than any other Magnesium has a lower density than any other structural metal and is an important metallurgical structural metal and is an important metallurgical reducing agent. Magnesium is also used in batteries reducing agent. Magnesium is also used in batteries and fireworks. and fireworks.
Calcium is used to reduce the oxides or fluorides of Calcium is used to reduce the oxides or fluorides of less common metals to the free metals. Calcium is less common metals to the free metals. Calcium is also alloyed with lead in lead–acid batteries, and is also alloyed with lead in lead–acid batteries, and is used to form other alloys with aluminum and silicon. used to form other alloys with aluminum and silicon.
The Group 2A Metals The Group 2A Metals and Living Matter and Living Matter Persons of average size have approximately 25 g of Persons of average size have approximately 25 g of magnesium in their bodies. magnesium in their bodies.
The recommended daily intake of magnesium for The recommended daily intake of magnesium for adults is 350 mg. adults is 350 mg.
Calcium is essential to all living matter. The human Calcium is essential to all living matter. The human body typically contains from 1 to 1.5 kg of calcium. body typically contains from 1 to 1.5 kg of calcium.
Strontium is not essential to living matter, but it is of Strontium is not essential to living matter, but it is of interest because of its chemical similarity to calcium. interest because of its chemical similarity to calcium.
Barium also has no known function in organisms; in Barium also has no known function in organisms; in ion is toxic. fact, the Ba2+2+ ion is toxic. fact, the Ba
Rainwater containing dissolved CO
Acidic rainwater converts CaCO
Chemistry of Groundwater Chemistry of Groundwater is acidic Rainwater containing dissolved CO22 is acidic due to formation of H22COCO33.. due to formation of H Acidic rainwater converts CaCO33 to Ca(HCO
to Ca(HCO33))22::
• As the water evaporates from the Ca(HCO3)2, the
somewhatsoluble salt forms CaCO3 again. Deposited CaCO3 leads to stalactites, stalagmites, and other cave formations.
), the hardness is --), the hardness is
Hard Water and Water Softening Hard Water and Water Softening is groundwater that contains Hard water is groundwater that contains Hard water significant concentrations of ions (Ca2+2+, , significant concentrations of ions (Ca MgMg2+2+, Fe, Fe2+2+) from natural sources. ) from natural sources. Hard water tends to precipitate soaps, Hard water tends to precipitate soaps, reducing their effectiveness. reducing their effectiveness. If the primary anion is the hydrogen If the primary anion is the hydrogen carbonate ion (HCO33 carbonate ion (HCO temporary hardness.. said to be temporary hardness said to be If the primary anions are other than If the primary anions are other than bicarbonate ion (Cl--, SO, SO44 )then the , HSO44 --)then the 2-2-, HSO bicarbonate ion (Cl permanent hardness.. hardness is called permanent hardness hardness is called
(cid:0) +
+Z
(
)
M HCO 3
MCO 3
CO 2
H O 2
(cid:0) (cid:0) (cid:0)
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
Temporary Hard Water Temporary Hard Water
ion. -- ion.
Contains HCO33 Contains HCO When heated gives When heated gives and H22O.O. 2-2-, CO, CO22 and H COCO33 reacts with The CO33 2-2- reacts with The CO multivalent ions to form multivalent ions to form precipitates. precipitates. (for example CaCO33, , (for example CaCO MgCOMgCO33))
Soften water by Soften water by precipitating the precipitating the multivalent ions using multivalent ions using slaked lime Ca(OH)22 slaked lime Ca(OH)
Permanent Hard Water Permanent Hard Water
Contains significant concentrations of Contains significant concentrations of anions other than carbonate. anions other than carbonate.
--.. , HSO44 For example SO44 2-2-, HSO For example SO and Usually soften by precipitating the Ca2+2+ and Usually soften by precipitating the Ca using sodium carbonate leaving MgMg2+2+ using sodium carbonate leaving sodium salts in solution. sodium salts in solution.
Bathtub ring is caused by Bathtub ring is caused by of and Ca2+2+ of salts of Mg2+2+ and Ca salts of Mg Palmitic acid Palmitic acid (a common soluble soap). (a common soluble soap).
Water Softening Water Softening
Ion exchange. Ion exchange. Undesirable Undesirable cations, Mg2+2+ cations, Mg and Fe3+ 3+ CaCa2+ 2+ and Fe are changed for are changed for ions that are ions that are not as not as undesirable, ex. undesirable, ex. NaNa++.. Resins or Resins or zeolites. zeolites.
Hard water with ions
Water Softening Water Softening by Ion Exchange by Ion Exchange
An ionexchange resin with acidic groups bound to Na+
As hard water passes through, hardwater cations are exchanged for Na+
Deionizing Deionizing
Instead of replacing cations with Instead of replacing cations with , they are replaced with H+.+. NaNa++, they are replaced with H Then the anions are replaced with Then the anions are replaced with OHOH--..
HH++(aq) + OH
(aq) + OH--(aq)
(aq) → H→ H22O(l)O(l)
Some studies have shown a weak inverse relationship 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 to allow for a recommendation for a level of hardness.
the sum of
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, sets some 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 the calcium and magnesium as 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.
o C
150
+ BeO Ti
2
2
+ Be TiO 2
2
2
(cid:0) (cid:0) (cid:0) (cid:0) (cid:0) (cid:0) (cid:0) + Ca H CaH
=- oH
610
kJ mol /
MgO
2
2
+ BeF Mg 2
+ Be MgF 2
+ Mg O 2
D (cid:0) (cid:0) (cid:0) (cid:0) (cid:0) (cid:0) (cid:0) (cid:0) (cid:0) (cid:0)
2
2
3
+ + (cid:0) (cid:0) (cid:0) NH 6 Mg OH 3 ( ) 2 Mg N 3 H O 2
4
+ + (cid:0) (cid:0) (cid:0) CH 4 2 Be OH ( ) Be C 2 H O 2
2 +
2
2
2
+ (cid:0) (cid:0) (cid:0) CaC 2 Ca OH ( ) H O 2 C H 2
2
2
+ (cid:0) + (cid:0) (cid:0) (cid:0) Mg H 2 Mg OH ( ) H O 2
2
2
3
Z + + (cid:0) (cid:0) (cid:0) MgCl NH Mg OH ( ) (cid:0) + 2 2 2 NH Cl 4 H O 2
+ + + (cid:0) (cid:0) (cid:0)
]
2
fuse
NaOH Be Na Be OH H 2 2 H O 2 ) ( 4 Natri hidroxoberilat
+
[ 2 +
Natri berilat
2
2
2
(cid:0) (cid:0) (cid:0) (cid:0) Be NaOH Na BeO H 2
