资源简介

(共38张PPT)
alkali metal
Lithium, Sodium, Potassium, Rubidium and Cesium
The common metals of this group are sodium (2.6% in the lithosphere, NaCl) and potassium (2.4%, KClMgCl2.6H2O, carnallite光卤石).
Salt mines are considered to be good places to leave radioactive waste because they are not subject to groundwater flow - that is why the salt got left there in the first place!
NaOH, Na2CO3, Na2SO4, Na3P3O9 and Na4SiO4 are among the top 50 industrial chemicals.
Potassium salts, notable K2SO4 or KNO3, are an important component of fertilizer.
Lithium alkyls are important reagents in synthesis.
Na+ and K+ are very important physiological ions, and Li+ salts are used to treat certain mental disorders.
Except Li, the chemistry is predominantly that of the M+ ions. There may be a hint of covalency in certain chelate complexes.
Li+ would have a ratio of charge/radius similar to Mg2+ hence certain similarities.
Other "look alikes" are NH4+ which is similar to K+ and Tl+ which is a bit like Rb+ or Ag+.
How do the alkali metals react with water
Reactions of the elements with water:
Group 1: M(s) + H2O(l) M+(aq) + (OH)-(aq) + H2(g)
Group 2: M(s) + 2 H2O(l) M+2(aq) + 2 (OH)-(aq) + H2(g)
These reactions are very exothermic and increase in violence from the lightest to the heaviest elements in the group (enough to ignite the H2 for the heavier elements). The non-reversible nature of this reaction means that such metals are very useful for drying many kinds of solvents.
The s-block metals are used as reducing agents for an immense number of different types of compounds.
More generally:
Group 1: M(s) + HOR M+ + (OR)- + H2(g)
Group 2: M(s) + 2 HOR M+2 + 2 (OR)- + H2(g)
These reactions make metal alkoxides that are very useful for the synthesis of other products using metathesis reactions. Metathesis indicates that the reagents exchange ligands with one another. Such reactions are especially favourable when it produces a metal halide because of the large exothermicity provided by the lattice or hydration energies.
e.g.’s MOR + ClPR’2 MCl + R’2POR
MNR2 + ClSiR’3 MCl + R’3SiNR2
One of the most important discoveries in synthetic chemistry was made by Victor Grignard (Nobel Prize 1912) following the initial work of others. He showed that the reaction of Mg with organic iodides (RI, later applied to other halides) results in the insertion of the Mg into the R-I bond. This provides a reagent of the form R-Mg-I that can be used in nucleophilic or metathesis reactions to make new carbon-carbon bonds.
Analogous and more reactive reagents can be made with Li and Na.
Mg(s) + R-I R-Mg-I
R-Mg-I + I-R R-R + MgI2
2 Li(s) + R-X R-Li + Li-X (X = halide)
R-Li + X-R’ R-R’ + Li-X
Such compounds were among the first that were recognized to contain bonds between metals and carbon. These were thus some of the initial examples of organometallic chemistry (one of the most studied branches of inorganic chemistry today).
Cp*2Mg
(Cp*Na THF)
DH°ie increases
DH°ie decreases
The s-block elements lose their electrons more easily than the other element in the main group so they are usually strong reducing agents and most tend to form ionic compounds. The stabilization that is provided by the crystal lattice (or hydration) energy of the salts they make helps to favour many reactions.
One of the stranger consequences of the low ionization enthalpy is observed when some of the group 1 metals are dissolved in appropriate solvents, such as liquid ammonia:
E.g.: Na(s) (dissolved in NH3 (l)) Na+(am) + e-(am)
Na+(am) + 2 (NH2)-(am) + H2(g)
At low concentration this is a blue solution that contains solvated electrons! If the reaction warms up or is catalyzed, the free electron reacts with the solvent to reduce some of the protons in the solvent to produce hydrogen gas:
This demonstrates the reducing ability of the alkali metals and is a very common and useful property of these elements.
X-ray crystal structure of [Cs+L2][e-]
Solutions of s-block metals in liquid NH3
group 1 metals and the group 2 metals Ca, Sr and Ba dissolve in liquid NH3 to give metastable solutions
Na + NH3 (liq)
Na+ + (NH3)n
.
_
solvated
electrons
The solution is
royal blue
SODIUM IN LIQUID AMMONIA
.
powerful reducing combination
(electron donor)
N
H
2
-
+
N
a
+
H
.
H
2
SODIUM-LIQUID AMMONIA CHEMISTRY
or Fe3+
Fe
(gas)
Royal blue
electron solution
Clear
sodium amide
solution
catalyst required
for this step
AMIDE ION
Strong Base
Reducing
Solution
x2
Dilute solutions of alkali metals in liquid NH3 have many
applications as reducing agents
Reaction with O2
Alkali metals form oxides when they are burnt in air. The nature of the oxides varies among the elements. For example lithium forms monoxide (Li2O), sodium forms peroxide (Na2O2) and the remaining elements mainly form superoxides with very little amounts of peroxides. These reactions are given as below:
4Li + O2 2 Li2O (Lithium monoxide)
Na + O2 Na2O2 (Sodium peroxide)
K + O2 KO2 (Potassium superoxide)
The reason for formation of peroxides and superoxides as we move down the group is due to increased stability of the larger cations through lattice energy.
Lithium on the other hand, due to stronger attraction exerted by the nucleus due to smaller size attracts the electrons strongly preventing the reaction with another oxygen atom. Hence, it forms only monoxide but not peroxide or superoxides.
F- Cl- Br- I-
Li+ 1036 853 807 757
Na+ 923 787 747 704
K+ 821 715 682 649
Rb+ 785 689 660 630
Cs+ 740 659 631 604
Lattice Energies of Alkali Metals Halides (kJ/mol)
fH & fG of oxides
H G H G H G
Li2O -597.9 -561.2 Li2O2 -634.3 -579.9
Na2O -414.2 -375.5 Na2O2 -510.9 -449.6 NaO2 -260.2 -218.4
K2O -361.5 -322.1 K2O2 -494.1 -425.1 KO2 -284.9 -239.4
Rb2O -339 Rb2O2 -472
Lange’s
The Crown Ethers
The alkali metals are complexed quite strongly by THF and glymes, but the effect becomes really marked for the so-called "crown ethers".
Interaction with Crown Ethers
Li+ is most strongly bound in dicylohexyl-14-crown-4
Na+ "fits" well in benzo-15-crown-5
Rb+ "fits" best in dicyclohexyl-21-crown-7
Cs+ "fits" best in dicyclohexyl-24-crown-8
The stability orders differ depending on the method of comparison (calculation, gas-phase, solution etc): experimentally in solution, it appears that any crown with –CH2CH2– bridges prefers K+ because of the 5-membered chelate ring size rather than the size of the hole on the crown - the macrocycle just puckers up to fit, but solvent effects may also be very important.
Cryptands and Cryptates
Cryptands are polycyclic cages, usually including nitrogen as well as oxygen to get the necessary junctions.
Metal ions are encapsulated even more securely inside them leading to cryptates.
Reaction with Cryptands
2 Na Na+ + Na-
When crypt-222 is added to ethylamine solution of Na, isolated product is [Na(crypt-222)]+Na-.
Golden yellow, diamagnetic solid.
Na- : sodide
[Cs(crypt-222)]+e-
Black, electride
Some remarkable compounds have been made:
2Na(NEt3) + 2,2,2-crypt
[Na(2,2,2-crypt)]+Na-(s)
Bear in mind that:
2Na Na+ + Na- H = 438 kJ mol-1
In chemistry a Zintl phase is the product of a reaction between
group 1 (alkali metals) or group 2 (alkaline earths) and
post transition metals or metalloids from group 13, 14, 15 or 16.
Zintl phases were named for the German chemist Eduard Zintl who investigated them in the 1930s.[1] The term "Zintl Phases was first used by Laves in 1941.[1]
Zintl phases are a subgroup of brittle, high melting point intermetallic compounds which are diamagnetic or exhibit temperature-independent paramagnetism, are poor conductors or semiconductors.[2] Zintl noted that there was an atomic volume contraction when these compounds were formed and realised this could indicate cation formation.[2] He suggested that the structures of Zintl phases were ionic, where there was complete electron transfer from the more electropositive metal.[2] The structure of the anion (nowadays called the Zintl ion) should then be considered on the basis of the resulting electronic state. These ideas were further developed to become the Zintl rule or Zintl Klemm concept, where the polyanion structure should be similar to an isoelectronic element.[1]
Examples of Zintl phases:
NaTl, where it is now known that the structure consists of a polymeric anion (-Tl -)n with a covalent diamond structure with Na+ ions fitted into the anionic lattice.[1]
NaSi where the polyanion is tetrahedral (Si4)4 similar to phosphorus molecule P4.[1]
Na2Tl which the polyanion is tetrahedral (Tl4)8 similar to phosphorus molecule P4.[3]
alkaline earth metal
Beryllium, Magnesium, Calcium, Strontium and Barium
Sources
Beryllium is found in the mineral beryl(绿柱石), Be3Al2(SiO3)6. Beryl with around 2.9% Cr3+ substituting for Al3+ is emerald(祖母绿).
Beryllium compounds are dangerously toxic and can pass through the skin - care!
The other elements are fairly common in a variety of minerals e.g. limestone, CaCO3, dolomite (白云石), CaCO3.MgCO3 and carnallite, KCl.MgCl(6H2O). Less common are strontianite(菱锶矿), SrCO3, and barytes(重晶石), BaCO3.
Radium, the bottom member of the group is radioactive with a half-life (226Ra)of about 1600 years as -emitter. It was first isolated from uranium ore, pitchblende(沥青铀矿), by M. and P. Curie, by laborious fractional crystallizations.
Beryllium
obtained by the reduction of BeCl2 by Ca or Mg or the Mg reduction of BeF2.
a very light metal, unreactive with air or water at ordinary temperatures.
dissolves in strong non-complexing acids (except HNO3 which passivates it) to give the [Be(H2O)4]2+ ion.
Be also dissolves in strong aqueous bases like NaOH to evolve hydrogen and yield the beryllate, Be(OH)42- ion.
Its amphoteric behavior is similar to aluminum.
Properties of Be Compounds
Beryllium compounds are fairly covalent and the chemistry is dominated by the Be attempting to obtain an octet
The simple Beryllium compounds can react with Lewis bases forming, for example, BeCl2(OEt2)2, and complex anions are also formed e.g. BeF42-, and [Be(H2O)4]2+.
Polymerization occurs through bridging groups to give chain polymers, e.g. (BeF2)n, (BeCl2)n and (Be(CH3)2)n. In the halides, the bridges are not electron deficient, but in the alkyls, three-centre, two-electron bonds must be invoked. For bulkier groups, for example certain alkoxides, the chain lengths can be reduced, or polymerization can even be inhibited
Basic beryllium acetate
Be4O(CH3CO2)6, which is soluble in non polar solvents e.g. benzene, has a tetrahedral arrangement of Be atoms around the oxygen atom, and an acetate bridging each of the six edges of the tetrahedron
Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water
AN OVERVIEW OF PHOTOSYNTHESIS
Carbon dioxide
Water
Glucose
Oxygen gas
PHOTOSYNTHESIS
THE OXYGEN EVOLVING CENTER
THE TYROSINE RADICAL BRIDGES THE WATER MOLECULE AND THE CHLOROPHYLL MOLECULE
Chlorophyll a & b
Chl a has a methyl group
Chl b has a carbonyl group
Porphyrin ring
delocalized e-
Phytol tail
Photosynthesis uses light energy to make food molecules
Light
Chloroplast
Photosystem II Electron transport chains Photosystem I
CALVIN CYCLE
Stroma
Electrons
LIGHT REACTIONS
CALVIN CYCLE
Cellular respiration
Cellulose
Starch
Other organic compounds
A summary of the chemical processes of photosynthesis

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