alkali metal

[ji ǎ n j ī n sh ǔ]

Metal element

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Alkali metal refers to periodic table of ele ments Six metal elements in Group IA except hydrogen (H), namely lithium （Li）、 sodium （Na）、 potassium （K）、 rubidium （Rb）、 cesium （Cs）、 Francium （Fr）。

according to IUPAC Alkali metals belong to group IA elements in the periodic table. The alkali metals all have an outermost electron belonging to the s orbital, so this group belongs to the s region of the periodic table of elements. The chemical properties of alkali metals show obvious homologous behavior Element periodicity The best example of. Although hydrogen (H) belongs to Group IA, its chemical properties are quite different from those of alkali metals, so it is not considered as an alkali metal.

Chinese name: alkali metal
Foreign name: alkali metal
Contains: Lithium, sodium, potassium, rubidium, cesium, francium

Periodic law of elements: From top to bottom, enhanced metallicity
Similarity property: Mostly silver white metal
Location: Family IA

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All discovered alkali metals exist in nature. According to the order of chemical element abundance, sodium is the highest, followed by potassium, followed by lithium, rubidium, cesium, and finally francium.

Crust

The following table shows the mass Clarke values of alkali metal elements in the crust (excluding ocean and atmosphere), taken from Inorganic Chemistry (Fifth Edition), 2008^[1] .371

element	lithium	sodium	potassium	rubidium	cesium
w（%）	0.006%	2.64%	2.60%	0.03%	0.0006%

It can be seen from the table that among alkali metals, potassium and sodium are major elements with large abundances, while lithium, rubidium and cesium are trace elements with small abundances. In seawater, the mass Clarke of sodium is 1.062%, and the mass Clarke of potassium is 0.038%. Potassium and sodium are also major elements in seawater.^[2]

mineralogy

Alkali metals have various minerals in nature, and the common minerals are as follows

Alkali metal minerals in nature
metal ion	mineral
lithium	Spodumene, lepidolite Lithium permeating feldspar
sodium	Common salt (sodium chloride), natural alkali (sodium carbonate), mirabilite（ Sodium sulfate decahydrate ）、 Chilean saltpeter (Sodium nitrate)
potassium	Nitrate (potassium nitrate), sylvite (potassium chloride), carnallite, potassium magnesite, alunite（ Potassium aluminum sulfate dodecahydrate ）
rubidium	Red mica, rubidium cesium ore
cesium	Rubidium cesium ore, cesium garnet

human body

Alkali metals exist in body fluids as ions in the human body, and also participate in the formation of proteins.

Alkali metal in human body mass fraction (%) Data source: Inorganic Chemistry (Fifth Edition), 2008.371

element	lithium	sodium	potassium	rubidium	cesium
Fresh weight	Extremely trace	0.15%	0.35%	Extremely trace	—

Note: The data may be quite different, and the following data can be checked: oxygen 65%, carbon 18%, hydrogen 10%

The element abundance in the human body is positively correlated with that in the crust, which is the result of the transmission of the biological chain. The mass fractions of potassium and sodium in animal embryos are similar, which is considered by some scholars as one of the evidences that animals originate from marine organisms.

effect

Most alkali metals have many uses. Rubidium or cesium atomic clock It is one of the most famous applications of soda metal, among which cesium atomic clock is the most accurate. A common use of sodium compounds is to make Sodium lamp , an efficient light source. Sodium and potassium are biological electrolyte , with important biological functions, belonging to dietary minerals 。

Alkali metal use
element	purpose
Lithium ion	Lithium has special effects in human brain. Research shows that lithium ion can cause adrenaline and Nerve endings The amount of amine in Neurotransmitter Because the specific mechanism of lithium ion action is not clear, there is no specific antidote for lithium poisoning, but lithium carbonate is currently widely used Manic depression Treatment (oral: 600mg~800mg/day).^[1]
Sodium ion	The osmotic balance of human body fluid is mainly regulated by sodium ion and chloride ion. Another important role of sodium ion is to regulate the charge inside and outside the neuron axon membrane. The concentration difference between sodium ion and potassium ion is the material basis of nerve impulse transmission, world health organization It is recommended that each person take (1-2) grams of sodium salt every day, Chinese Nutrition Society It is recommended not to exceed 5g.^[1]
Potassium ion	Potassium is also involved in regulating osmotic pressure and axon The charge inside and outside the membrane is rich in potassium in the heart, liver, spleen and other organs of the human body.^[1]
Rubidium element	The physiological function of rubidium is still under study. There are many signs indicating that rubidium is related to life process, which is suspected to be trace element 。^[3]

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Basic property table

element	3 Li	11Na (Sodium)	19K (potassium)	37Rb	55Cs (cesium)	87Fr
Melting point/℃	one hundred and eighty point five	ninety-seven point eight one	sixty-three point six five	thirty-eight point eight nine	twenty-eight point eight four	twenty-seven
Boiling point/℃	one thousand three hundred and forty-seven	eight hundred and eighty-two point nine	seven hundred and seventy-four	six hundred and eighty-eight	six hundred and seventy-eight point four	six hundred and seventy-seven
Melting boiling point change	Downtrend
Density (25 ℃)/g · cm ^ - 3	zero point five three four	zero point nine seven one	zero point eight five six	one point five three two	one point eight seven eight five	one point eight seven zero
Density change	Upward trend		abnormal
Conductivity	conductor	conductor	conductor	conductor	conductor	conductor
colour	silvery white	silvery white	silvery white	Silver white (slightly golden)	golden	silvery white
form	solid	solid	solid	solid	solid	solid
Metallic or non-metallic	Metallicity	Metallicity	Metallicity	Metallicity	Metallicity	Metallicity
Valence state	+1	+1	+1	+1	+1	+1
Main oxides	Li2O	Na2O Na2O2	K2O K2O2	complex	complex	complex
Hydrate corresponding to oxide	LiOH	NaOH	KOH	RbOH	CsOH	FrOH
Gaseous hydride	LiH	NaH	KH	RbH	CsH	FrH
Stability of gaseous hydride	instable	instable	instable	instable	instable	instable
hardness	Gradually decrease (pay attention to the storage method)

Periodic law property

Alkali metals are in Group IA, and their periodic properties are mainly shown as

Top-down Metallicity Gradually increase (the metallicity of elements can be determined from the difficulty of replacing hydrogen by its simple substance reacting with water or acid, or the hydrate of their highest valence oxide—— hydroxide To infer the alkalinity of^[2] ）

Each alkali metal element is the most metallic element in the same period.

Alkali metals have many similar properties: they are mostly silvery white metals (cesium shows golden yellow luster), with low density, low melting point and boiling point, Standard status There are very high Reactivity ； They are easy to lose valence electron Form+1 charged cation ； They are soft and can be cut with a knife to reveal a silvery white section; Because of the reaction with oxygen in the air, the cut surface soon loses its luster. Due to the active chemical properties of alkali metals, they are generally placed in mineral oil In or sealed in Noble gas To prevent reaction with air or water. In nature, alkali metals are only found in salt and never exist in the form of simple substance. Alkali metals can react violently with water to form strong alkaline hydroxide, and Relative atomic mass The stronger the reaction ability is.

Simple substance and ion

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physical property

Alkali metal elements (lithium cesium from left to right)

Alkali metal elements are mostly Metallic luster It is a silvery white metal (cesium with golden yellow), but when exposed to the air, it will form an oxide film due to the oxidation of oxygen, which will reduce the gloss, showing gray. The density of alkali metal elements is less than 2g · cm ^ - 3, which is a typical light metal. Lithium, sodium and potassium can float on water, and lithium can even float in kerosene; The crystal structure of alkali metal elements is body centered cubic stacking, and the stacking density is small, Mohs hardness Less than 2, soft, excellent electric and thermal conductivity. Alkali metals can interact with mercury（ Hg ）Forming alloy（ Amalgam )。^[1]

Flame reaction (Physical properties)

Alkali metal ions and their volatile compounds will show a unique color when burning in a colorless flame, which can be used to identify the existence of alkali metal ions. Lithium, rubidium and cesium are also discovered by chemists in this way. Electronic transitions can explain the flame reaction and the absorption of alkali metal ions spectrum It falls in the visible light area, so the symbolic color appears.

In addition to identification, flame color reaction can also be used to produce fireworks and flares.

The following table shows the flame reaction related tables of alkali metal ions, and the wavelength data is taken from Inorganic Chemistry (Fifth Edition), 2008^[1] three hundred and eighty

category	lithium	sodium	potassium	rubidium	cesium
colour	Purplish red	yellow	Lilac	purple	blue
Wavelength/nm	six hundred and seventy point eight	five hundred and eighty-nine point two	seven hundred and sixty-six point five	seven hundred and eighty	four hundred and fifty-five point five

chemical property

Alkali metallic Standard electrode potential Very small, with strong reactivity, and can directly interact with many Nonmetallic element formation Ionic compound It reacts with water to generate hydrogen, which can reduce many salts (such as titanium tetrachloride). Except lithium, all alkali metal elements cannot be directly combined with nitrogen.

chemical property
Reaction object	Reaction equation
React with water	2Li+2H two O=2LiOH+H two (g) 2Na+2H two O=2NaOH+H two (g) 2K+2H two O=2KOH+H 2( g)
React with oxygen	4Li（s）+O₂（g）=2Li two O（s） 4Na（s）+O₂（g）=2Na two O（s） 2Na（s）+O₂（g）=Na two O₂（s） R（s）+O₂（g）=RO two （s） R=K、Rb、Cs
Reaction with halogen (X)	2R（s）+X₂（g）=2RX（s）
React with hydrogen (H ₂)	2R (s)+H ₂ (g)=high temperature=2RH (s)
React with sulfur	2R (s)+S (s)=R2S (s), reaction explosion
React with phosphorus	3R（s）+P（s）=R three P（s）
Lithium reacts with nitrogen	6Li（s）+N two （s）=2Li three N（s）

Thermodynamic electrochemistry

Relevant thermodynamic and electrochemical data of alkali metals are as follows:^[1]

Electronics Affinity Data from Chemistry - Structure and Properties of Substances (Elective), 2007^[4] .24

All units are standard units

category	lithium	sodium	potassium	rubidium	cesium
Standard molar sublimation enthalpy	one hundred and fifty-nine point three seven	one hundred and seven point three two	eighty-nine point two four	eighty point eight eight	seventy-six point zero six five
Standard molar hydration enthalpy	-535.27	-420.48	-337.64	-312.27	-287.24
Standard molar formation enthalpy of ions (aq)	one hundred and fifty point five one	one hundred and eighty-eight point eight eight	one hundred and seventy-six point six two	one hundred and seventy-seven point eight three	one hundred and seventy point seven two
First ionization energy (I)	five hundred and twenty-six point four one	five hundred and two point zero four	four hundred and twenty-five point zero two	four hundred and nine point two two	three hundred and eighty-one point nine zero
Electronic affinity (E)	fifty-nine point six	fifty-two point nine	forty-eight point four	forty-six point nine	forty-five point five
Standard electrode potential E ⊕	-3.040	-2.714	-2.936	-2.943	-3.027

It can be seen from the table that the standard electrode potential of alkali metal is about -3.000V, indicating that its simple substance is easy to lose electrons, ionization energy With the increase of electron affinity energy and the decrease of electron affinity energy, it shows that the reducibility of its simple substance is increasing. The standard molar hydration enthalpy of lithium is the largest, but in fact, lithium and water are the least reactive. This is because the standard molar sublimation enthalpy of lithium is too large, and compared with other alkali metals, the water solubility of lithium hydroxide, the reaction product of lithium and water, is much smaller. During the reaction with water, lithium hydroxide is covered on lithium, The reaction is affected.^[1]

Particularity of lithium

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Anomaly of lithium

The periodicity of Group IA is very obvious, but lithium is very different from other alkali metal elements of the same family. This difference is mainly manifested in the covalence of lithium compounds, which is caused by the small atomic radius of lithium.

Diagonal rule

periodic table of ele ments Medium, alkali Lithium metal And alkaline earth magnesium at its diagonal position（ Mg ）There is a certain similarity, which reflects the local existence of“ Diagonal rule ”。 The similarities between lithium and magnesium are as follows:

(1) Normal oxide is generated by the interaction of simple substance and oxygen

(2) The simple substance can be directly combined with nitrogen (other alkali metal simple substances of the same family as lithium have no such property)

(3) Fluoride, carbonate and phosphate are insoluble in water

(4) Carbonate is easy to decompose when heated

The reason is that the lithium magnesium diagonal rule can be explained by the change of the ion radius in the periodic table. In the same period, from left to right, the ion radius decreases with the increase of the effective charge, and the ion radius of the same family elements increases from top to bottom with the increase of the number of electronic layers. Since lithium and magnesium are at the diagonal, magnesium is just at the "bottom right" of lithium, Its ion radius decreases with the gradual change of the period and increases with the gradual change of the family. After the two cancel out, the similarity appears.^[3]

chemical compound

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Compound properties

Among the various compounds formed by alkali metal elements, alkali metal cations have no special properties, and the properties of alkali metal compounds are mostly reflected in the properties of anions.

inorganic salt

The salts of alkali metals are mostly ionic crystals, and most of them are soluble in water, among which the insoluble salts are
Lithium salt	Lithium fluoride 、 Lithium carbonate 、 Lithium phosphate^[1]
sodium salt	Sodium uranyl zinc acetate 、 Sodium hexahydroxytin (Ⅳ) acetate^[1] 、 Sodium titanate 、 Sodium bismuth 、 Sodium hexahydroxy antimonate
sylvite	Potassium sodium hexanitrocobalate 、 Potassium perchlorate 、 Potassium tetraphenylborate^[1] 、 Potassium perrhenate
Rubidium salt and cesium salt	Same as potash, but less soluble.

The melting and boiling points of alkali metal salts are high. The following table is the melting points of alkali metal salts. This table is taken from Inorganic Chemistry (Fifth Edition), 2008^[1] .387

Unit: m.p./℃

	lithium	sodium	potassium	rubidium	cesium
chloride	six hundred and thirteen	eight hundred and one	seven hundred and seventy-one	seven hundred and fifteen	six hundred and forty-six
sulfate	eight hundred and fifty-nine	eight hundred and eighty	one thousand and sixty-nine	one thousand and fifty	one thousand and five
Nitrate	～225	three hundred and seven	three hundred and thirty-three	three hundred and five	four hundred and fourteen
carbonate	seven hundred and twenty	eight hundred and fifty-eight	nine hundred and one	eight hundred and thirty-seven	seven hundred and ninety-two

It can also be observed from the table that the boiling point of lithium salt is obviously low, indicating that lithium salt shows certain covalence

	Principle and application	Reaction equation
halide	Alkali halide Common in sodium chloride And potassium chloride, which are abundant in seawater. Electrolysis of saturated sodium chloride can produce chlorine, hydrogen and sodium hydroxide This is a method for industrial production of sodium hydroxide and chlorine.	Anode: 2Cl - －2e - ——→Cl₂↑ Cathode: 2H + +2e - ——→H₂↑ Total reaction: 2NaCl+2H two O -- Electrolysis → 2NaOH+H ₂ ↑+Cl ₂ ↑
sulfate	Sodium sulfate is the most common alkali metal sulfate. Sodium sulfate decahydrate, commonly known as mirabilite, is used for phase change heat storage, Anhydrous sodium sulfate Commonly known as sodium sulfate, it is used in glass and ceramic industries and in the production of other salts.^[1]
Nitrate	Nitrate of alkali metal decomposes into nitrite 。	2MNO₃（s）——→2MNO₂（s）+O₂（g） potassium nitrate （ KNO₃ ）And Sodium nitrate （ NaNO₃ ）It is a common nitrate and can be used as an oxidant
carbonate	Among alkali metal carbonates, lithium carbonate can be obtained by reacting lithium containing minerals with sodium carbonate. It is the raw material for making other lithium salts, and can also be used for the treatment of manic depression; Sodium carbonate, commonly known as soda ash, is an important industrial raw material, mainly composed of Hou's soda process Production.^[1]	NH₃（g）+H2O（l）+CO₂（g）——→NH4HCO₃（aq） NH four HCO₃（aq）+NaCl（s）——→NH four Cl（aq）+NaHCO₃（s） 2NaHCO₃（s）—△→Na two CO₃（s）+H two O（l）+CO₂↑（g）

Organometal

Alkali metallic Organometallic compound It has important applications in organic synthesis. The following is a brief introduction of common species

Alkyl lithium

Potassium ion and&

There are bridge bonds (LI-C-Li) in alkyl lithium to Tetramer The carbon lithium bond in alkyl lithium has covalent bond Characteristics of, where Buli Volatile and capable of Vacuum distillation This is an example.^[5] Alkyl lithium is strong Nucleophile , nucleophilic ability is better than Grignard reagent , can initiate all the addition reactions of the latter, and has higher yield, but poor stereoselectivity; Alkyl lithium has small steric hindrance and is less affected by space effect during reaction, so it can be used to synthesize alcohol with large steric hindrance. In addition, alkyl lithium and copper (I) halide Can form Dialkyl copper lithium It also has important applications in organic synthesis. Alkyl lithium is easy to react with water, so it should be thoroughly dried during preparation.^[6]

Sodium alkynyl

1-alkyne can form sodium alkynyl with sodium in liquid ammonia. Sodium alkynyl is a nucleophile, which can react with halogenated hydrocarbons to prepare derivatives of alkyne or grow carbon chains. In addition, it can also react with Acyl halide Reaction preparation Alkynyl ketone However, it is seldom used in organic synthesis, and its substitute is alkynyl copper (I) compound.^[6]

oxide

See the following for relevant properties of alkali metal normal oxides, taken from Inorganic Chemistry (Fifth Edition), 2008^[1] .383

All units are standard thermodynamic units

category	Lithium oxide	Sodium oxide	Potassium oxide	Rubidium oxide	Cesium oxide
colour	white	white	Yellowish	Bright yellow	Orange red
Melting point/K	one thousand seven hundred and forty-three point one five	one thousand and ninety-three point one five	～ 523.15 (decomposition)	～ 573.15 (decomposition)	～ 663.15 (decomposition)
Standard molar enthalpy of formation	-597.9	-414.22	-361.5	-339	-345.77

oxide	Principle and application	Reaction equation
Normal oxide	Alkali metals and oxygen can form various complex oxides. Among alkali metals, only lithium can be directly burned in oxygen to form a single oxide, while other alkali metal elements generally form peroxides/superoxide	4Li（s）+O₂（g）——→2Li2O（s）
Normal oxide	The normal oxide of alkali metal is diamagnetic material, which can react with water to generate corresponding hydroxide	M2O（s）+H2O（l）——→MOH（aq）
peroxide	All alkali metals can form peroxides. Except lithium, other alkali metals can be directly combined to form peroxides. The peroxides of alkali metals are light yellow	2M（s）+O₂（g）——→M2O₂（s）
	The oxygen element in peroxide exists in the form of peroxide anion, and the bond order of peroxide ion is 1. Peroxide is a strong base (proton base), which can react with water to form a less alkaline hydroxide and hydrogen peroxide Due to a large amount of exothermic reaction, the generated hydrogen peroxide will rapidly decompose to produce oxygen.	2M2O₂（s）+2H2O（l）——→4MOH（aq）+O₂（aq） 2H2O₂（aq）——→2H2O（l）+O₂（g）
	Peroxides can be mixed with Acid oxide Corresponding Orthosalt If the acid oxide reacted with it has strong reducibility, it may be oxidized	2M2O₂（s）+2CO₂（g）——→2M2CO₃（s）+O₂（g） M2O₂（s）+SO₂（g）——→2M2SO₄（s）
	Peroxide can form oxyacid salt with some platinum elements in molten state	Ru（s）+3M2O₂（l）——→M2RuO₄（s）+2M2O（l）
	The common peroxides are Sodium peroxide (Na2O ₂) and Potassium peroxide (K2O ₂), which can be used for bleaching, ore melting and oxygen generation.
Superoxide	Except lithium, all alkali metal elements have corresponding superoxide. Potassium, rubidium and cesium can be directly combined in the air to obtain superoxide. Potassium superoxide is light yellow to orange yellow, rubidium superoxide is brown, and cesium superoxide is dark yellow.	M（s）+O₂（g）——→MO₂（s）
	There are superoxide ions in the superoxide, and the molecular orbital indicates that there is a σ Bond and a three electron π bond, with bond order of 3/2, are paramagnetic. Superoxide can react with water to generate corresponding hydroxides, oxygen and hydrogen peroxide. The reaction is exothermic and hydrogen peroxide decomposes.	2MO₂（s）+2H2O（l）——→2MOH（aq）+H2O₂（l）+O₂（g） 2H2O₂（aq）——→2H2O（l）+O₂（g）
	Superoxide can react with acid oxide, similar to peroxide, in which, Potassium superoxide And carbon dioxide The response was applied to the emergency air bag. Potassium superoxide is the most common superoxide.	4MO₂（s）+2CO₂（g）——→2M2CO₃（s）+3O₂（g）
Ozone oxide	In addition to lithium, dry alkali metal hydroxide solid reacts with ozone (O ∨), and the product recrystallizes in liquid ammonia to obtain ozone oxide crystal.	6MOH（s）+4O₃（g）——→4MO₃（s）+2MOH·H2O（s）+O₂（g）
Ozone oxide	The ozone oxide decomposes slowly during storage. Ozone ion exists in ozone oxide, V-shaped structure, bond level of 1/3, extremely unstable, paramagnetic. Other properties of ozone oxides are similar to those of superoxide.	2MO₃（s）——→2MO₂（s）+O₂（g）
hydride	When alkali metal is heated in hydrogen gas stream, corresponding hydride	2M（s）+H₂（g）——→2MH（s）
hydride	Among alkali metal hydrides, lithium hydride (LiH) is the most stable and decomposes at 850 ℃. Alkali metal hydride belongs to Ionic hydride , high melting and boiling point, sodium chloride type crystal structure, hydrogen anion exists in alkali metal hydride, and hydrogen can be obtained by electrolysis of lithium hydride dissolved in lithium chloride at the anode, which can prove the existence of hydrogen anion. Alkali metal hydride reacts violently with water to release hydrogen.	MH（s）+H2O（l）——→MOH（aq）+H₂（g）
hydroxide	The hydroxide of alkali metal element is a white solid at room temperature, which is easily soluble in water and emits a lot of heat when dissolved in water. It will deliquescence in the air and absorb acid gas; Alkali metal hydroxides belong to strong alkalis and are completely ionized in water. In alkali metal hydroxide, sodium hydroxide and Potassium hydroxide It is the most common and can be used as a desiccant.	2MOH（s）+CO₂（g）——→M2CO₃（s）+H2O（l） 2MOH（aq）+2Al（s）+2H2O（l）——→2MAlO₂（aq）+3H₂（g） 2MOH（aq）+Al2O₃（s）——→2MAlO₂（aq）+H2O（l） 3MOH（aq）+FeCl₃（aq）——→Fe（OH）₃（s）+3MCl（l）
Chelate	crown ether complex compound: There is a cavity with a specific size in the center of the crown ether, which can form a complex with alkali metal ions.	Common ones: lithium ion: 12-Crown-4 ； Sodium ion: 15-crown-5 ； Potassium ion: 18-crown-6 。
	Cryptate ether complex compound: Alkali metal ions can also be complexed with hole ethers, and the resulting complexes are more stable than crown ether complexes.	Common: potassium ion: [2.2.2] Cavalier 。
	Application: surface active agent （ surfactant ）； phase transfer catalyst （ Phase transfer catatysis PTC）； Separate corresponding alkali metal ions

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