Subfamily elements

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This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Sub group elements are represented by B, including IIIB 〜 VIIB family elements , Group I B, Group II B elements and Group VIII elements. For group IIIB-VIIB elements, the total number of valence electrons is equal to the number of its family number, which is also equal to the sum of the number of ns electrons in the outermost layer of the atom and the number of (n-1) d electrons in the secondary layer. Since the (n-1) d sublayer of the I B and II B families has been filled, the number of s electrons on the outermost layer is equal to the number of their families. Group VIII is in the middle of the periodic table, with three vertical rows, and the last electron is filled in the (n - 1) d sublayer.

Chinese name: Subfamily elements

Foreign name: subgroup B element
Discipline: Chemistry

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one definition
two general survey
three Paragroup elements and their compounds

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Subgroup elements (represented by "B"): all elements on the (n-1) d or (n-2) f sublayer filled with the last electron belong to the sub group elements, also known as Transitional element (Lanthanides and actinides are called internal transition elements).^[1]

general survey

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d Zone elements refer to IIIB-VIII elements, ds Area elements refer to IB and IIB family elements. d The periphery of the zone element Electronic configuration Yes（ n －1) dns (Pd exception), ds The peripheral electronic configuration of the region element is（ n －1) dns 。 They are distributed in cycles 4, 5 and 6, and we mainly discuss the d Zone and ds Zone element.

Cycle 4 d District ds Some properties of zone elements

	Sc three d four s	Ti three d four s	V three d four s two	Cr three d four s	Mn three d four s	Cu three d four s	Zn three d four s
Melting point/℃	one thousand nine hundred and fifty-three	one thousand six hundred and seventy-five	one thousand eight hundred and ninety	one thousand eight hundred and ninety	one thousand two hundred and four	one thousand and eighty-three	four hundred and nineteen
Boiling point/℃	two thousand seven hundred and twenty-seven	three thousand two hundred and sixty	three thousand three hundred and eighty	two thousand four hundred and eighty-two	two thousand and seventy-seven	two thousand five hundred and ninety-five	nine hundred and seven
Atomic radius /Pm	one hundred and sixty-four	one hundred and forty-seven	one hundred and thirty-five	one hundred and twenty-nine	one hundred and twenty-seven	one hundred and twenty-eight	one hundred and thirty-seven
M radius/Pm	－	ninety	eighty-eight	eighty-four	eighty	seventy-two	seventy-four
I 1kJ·mol	six hundred and thirty-one	six hundred and fifty-eight	six hundred and fifty	six hundred and fifty-two point eight	seven hundred and seventeen point four	seven hundred and forty-five point five	nine hundred and six point four
Room temperature density/gcm	two point nine nine	four point five	five point nine six	seven point two zero	seven point two zero	eight point nine two	seven point one four
Oxidized state	three	–1,0,2 3,4	–1,0,2 3,4,5	–2,–1,0 2,3,4 5,6	–1,0,1 2,3,4 5,6,7	1,2 three	(1) two

*() is in unstable oxidation state.

Coeval d Zone or ds Area elements have many similarities, such as Metallicity The gradual change is not obvious Atomic radius 、 Ionization potential Equivalency Atomic number Although the increase has changed, it is not significant, which reflects that d Zone or ds Horizontal similarity of area elements from left to right.

d Zone or ds Area elements have many common properties:

periodic table of ele ments

(1) They are all metals, because they have only one or two electrons in the outermost layer. They have high hardness and high melting and boiling points. The elements in d zone of the fourth cycle are relatively active metals, which can replace hydrogen in acid; But in the 5th and 6th cycle d Regional elements are less active, and they are difficult to interact with acids.

(2) With a few exceptions, they all exist in many ways Oxidized state , and the difference between two adjacent oxidation states is 1 or 2, such as Mn, which has – 1, 0, 1, 2, 3, 4, 5, 6, 7; and p The difference between two adjacent oxidation states of a zone element is usually 2, such as Cl, which has – 1, 0, 1, 3, 5, 7 and other oxidation states. The highest oxidation state is equal to the family number, except for family VIII. Cycle 4 d The compounds in the highest oxidation state of zone elements are generally unstable; The 5th and 6th cycles d The compounds in the highest oxidation state of the elements in the zone are relatively stable, and the compounds in the highest oxidation state are mainly oxides Oxyacid or fluoride Exists in the form of, such as WO3 , WF6, MnO, CrO, etc., the compounds in the lowest oxidation state are mainly Complex Form exists, such as [Cr (CO) 5]

(3) Their Hydrated ion and Acid radical ion It often presents a certain color. The color of these ions is unpaired with their ions d Electrogenesis transition of

some d Color of hydrated ions of elements in the zone

Electronic configuration	Unpaired Number of electrons	cation	Hydrated ion colour
three d	zero zero	Sc Ti	colourless colourless
three d	one one	Ti V	violet blue
three d	two	V	green
three d	three three	V Cr	violet violet
three d	four four	Mn Cr	violet blue
three d	five five	Mn Fe	Flesh color lilac colour
three d	four	Fe	green
three d	three	Co	Pink
three d	two	Ni	green
three d	one	Cu	blue
three d	zero	Zn	colourless

The colors of common acid radical ions are:

CrO (yellow), Cr2O (orange) MnO4 (2 –) (green), MnO4 (–) (magenta).

(4) Their atom Or ion formation Complex The tendency is relatively large. Because of their Electronic configuration With acceptance ligand Lone electron pair Conditions.

These properties are related to their Electronic layer Structure.^[2]

Paragroup elements and their compounds

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Titanium subfamily

1. Basic properties of titanium paragroup elements

Titanium paragroup element atom Of valence electron The layer structure is（ n －1) dns Therefore, titanium, zirconium and hafnium are the most stable Oxidized state It is+4, followed by+3, and the+2 oxidation state is relatively rare. In individual Coordination compound In addition, titanium can also be in the low oxidation state of 0 and – 1. The tendency of zirconium and hafnium to form low oxidation state is smaller than that of titanium. Their M (Ⅳ) compounds are mainly covalent bond combination. stay aqueous solution It mainly exists in the form of MO and is easy to hydrolysis 。 because Lanthanide Shrinkage, hafnic Ionic radius It is close to zirconium, so their chemical property Very similar, resulting in difficulty in separating zirconium and hafnium.

2. Titanium and its compounds

(1) Titanium

Titanium is an active metal, which can directly interact with most of the Nonmetallic element Reaction. At room temperature, titanium does not Inorganic acid Reaction, but soluble in concentrated and hot hydrochloric acid and sulfuric acid:

2Ti+6HCl (thick)=2TiCl3+3H2 ↑

2Ti+3H2SO4 (rich)=2Ti2 (SO4) 3+3H2 ↑

titanium Soluble to hydrofluoric acid Or in acid containing fluorine ion:

Ti + 6HF =【TiF6】（2- ）+2H（+） + 2H2↑

（2） titania

Titanium dioxide in nature rutile It is the most important, insoluble in water and dilute acid, but soluble in hydrofluoric acid and hot concentrated sulfuric acid Medium:

TiO2 + 6HF= H2[TiF6]+ 2H2O

TiO2 + 2H2SO4（thick）=2Ti(SO4)2 + 2H2O

TiO2 + H2SO4（thick）=2TiOSO4 + H2O

（3） Titanium tetrachloride

Titanium tetrachloride is an important kind of titanium halide Using it as raw material, a series of titanium compounds and Metallic titanium 。 It is very easy in water or humid air hydrolysis It will smoke when exposed to the air:

TiCl4 + 2H2O = TiO2 + 4HCl

(4) Titanic Coordination compound

Titanium (Ⅳ) can be formed with many additives Complex , such as [TiF6], [TiCl6], [TiO2 (H2O2)], among which the complexes with H2O2 are more important. This reaction can be used for titanium Colorimetric analysis , Join ammonia Yellow peroxide is generated Titanic acid H4TiO6 precipitation is a sensitive method for qualitative detection of titanium.^[2]

Vanadium subgroup

1. Basic Properties of Vanadium Subgroup Elements

The vanadium subgroup includes vanadium, niobium and tantalum, whose Valence electron layer Structure is（ n -1) dns , 5 valence electron Can participate in bonding, so the highest Oxidized state Is+5, equivalent to d It is the most stable oxidation state of vanadium group elements. The stability increases in order of V, Nb, Ta, and the stability of low oxidation state decreases in order. Niobium and tantalum have similar properties due to their similar radii.

2. Vanadium and its compounds

(1) Vanadium

Vanadium is easy to be passivated, therefore normal atmospheric temperature Lower activity. Lump vanadium does not react with air, water Caustic alkali Function is not related to non Oxidizability Acid action, but soluble in hydrofluoric acid , also soluble in strong oxidizing acids (such as nitric acid and Aqua regia ）Medium. At high temperatures, vanadium and most Nonmetallic element And can react with molten caustic soda.

（2） Vanadium pentoxide

V2O5 can be decomposed by heating Ammonium metavanadate or Vanadium trichloride oxide Of hydrolysis And the result is:

2NH4VO3=V2O5 + 2NH3 + H2O

2VOCl3 + 3H2O = V2O5 + 6HCl

Used in industry Chlorination roasting Legal treatment Vanadite , extracting vanadium pentoxide.

V2O5 It is more acidic and oxidizing than TiO2. It is mainly acidic and soluble in alkali

V2O5 + 6NaOH = 2Na3VO4 + 3H2O

It can also dissolve in strong acid VO (2+) ions are generated in (pH<1). V2O5 is a strong oxidant:

V2O5 + 6HCl = 2VOCl2 + Cl2↑+ 3H2O

（3） Vanadate And polyvanadate

Vanadates include metavanadate MVO3, orthovanadate M3VO4 and polyvanadate (M4V2O7, M3V3O9). Only when the total concentration of vanadium in the solution is very dilute (less than 10 mol · L) and the solution is strongly alkaline (pH>13) Acid radical Can exist stably in solution; When the pH drops and the total concentration of vanadium in the solution is less than 10 mol · L, the acid vanadium in the solution Acid radical ion In the form of HVO, H2VO; When the total concentration of vanadium in the solution is more than 10 mol · L, there are a series of polymer species (polyvanadates) in the solution, such as V2O, V3O, V4O, V10O, etc.^[2]

Chromium subfamily

1. Basic Properties of Chromium Subgroup

The VIB group of the periodic system includes chromium, molybdenum and tungsten. Chromium and molybdenum Valence electron layer Structure is（ n -1) dns , tungsten is（ n -1) dns 。 Their highest Oxidized state Is+6, both have d The characteristics of various oxidation states of regional elements. The stability of their highest oxidation state increases in the order of Cr, Mo, W, while the stability of their low oxidation state is opposite.

2. Chromium and its compounds

(1) Chromium

Chromium is active and soluble in dilute HCl H2SO4 , blue Cr solution is generated at first, and then oxidized by air to green Cr solution:

Cr + 2HCl = CrCl2 + H2↑

4CrCl2 + 4HCl + O2 = 4CrCl3 + 2H2O

Chromium in cold and concentrated HNO3 passivation 。

(2) Chromium (III) compounds

Add 2 mol · dm NaOH drop by drop into Cr (3+) solution to generate grayish green Cr (OH) 3 precipitation. Cr (OH) 3 is bisexual:

Cr(OH)3 + 3H（3+） = Cr （3+）+ 3H2O

Cr (OH) 3+OH (–)=Cr (OH) 4 (–) (bright green)

Chromium (III) Complex coordination number Are all 6 (with a few exceptions), and the space configuration of their mononuclear complexes is Octahedron 6 Cr (3+) ions Empty orbit , forming six dsp Hybrid orbit 。

（2） Chromic acid 、 chromate and Dichromate

If acid is added to the yellow CrO (2 –) solution, the solution will become orange Cr2O7 (2 –)（ Dichromate Root) solution; On the contrary, alkali is added to the orange Cr2O7 (2 –) solution, which turns into CrO (2 –) yellow solution:

2CrO (2 –) (yellow)+2H (+)=Cr2O7 (2 –) (orange)+H2O K = 1.2×10

H2CrO4 is a stronger acid (pH=4.1, K=3.2 × 10), which only exists in aqueous solution Medium.

Chromium chloride Acyl CrO2Cl2 is a blood red liquid, which is easy to decompose in water:

CrO2Cl2 + 2H2O = H2CrO4 + 2HCl

common Insoluble Chromates include Ag2CrO4 (brick red), PbCrO4 (yellow), BaCrO4 (yellow) and SrCrO4 (yellow), which are soluble in strong acid Generate M and Cr2O7 (2 –).

K2Cr2O7 is commonly used Strong oxidant (=1.33 V) Saturated K2Cr2O7 solution and concentrated H2SO4 mixture are used as the laboratory lotion. It is much easier to oxidize Cr (OH) 4 to CrO in alkaline solution than to oxidize Cr to Cr2O in acidic solution. The conversion of Cr (VI) to Cr (III) is usually carried out in acid solution.

3. Important compounds of molybdenum and tungsten

(1) Oxide of molybdenum and tungsten

MoO3 , WO3 and CrO3 Different, they are insoluble in water, only soluble in ammonia And strong alkali solution to generate corresponding oxylate.

(2) Molybdenum and tungsten Oxyacid And its salts

Molybdic acid 、 Tungstic acid And Chromic acid Different, they are Insoluble Acid Oxidizability Both are weak, molybdenum and tungsten Oxyates Only the salts of ammonium, sodium, potassium, rubidium, lithium, magnesium, silver and thallium (I) are soluble in water, and the rest of oxyacid salts are insoluble in water. The oxidation is very weak, and only strong can be used in acidic solution reducing agent To restore them to+3 Oxidized state 。^[2]

Manganese subfamily

1. Basic Properties of Manganese Subgroup

Group Ⅶ B includes manganese, technetium and rhenium. Only manganese and its compounds have great practical value. Like other sub group elements, the high oxidation state from Mn to Re tends to be stable. On the contrary, Mn is the most stable in the low oxidation state.

2. Manganese and its compounds

(1) Manganese

Manganese is an active metal and forms an oxide protective film on its surface in the air. Manganese in water due to surface formation Manganese hydroxide And prevent the reaction from continuing. Manganese and strong acid The reaction generates Mn (II) salt and hydrogen. But it reacts slowly with cold concentrated H2SO4（ passivation ）。

(2) Compounds of manganese (II)

Mn is stable in acid medium. However, Mn (II) is easily oxidized to Mn (IV) compound in alkaline medium.

Mn(OH)2 Is white Insoluble Things, Ksp =4.0 × 10, easily oxidized by air, and even a small amount of oxygen dissolved in water can oxidize it into brown MnO (OH) 2 precipitation.

2Mn(OH)2 + O2 = 2MnO(OH)2↓

Mn is oxidized only when it meets strong oxidants (NH4) 2S2O8, NaBiO3, PbO2 and H5IO6 in acid medium.

2Mn（2+）+ 5S2O8（2–） + 8H2O = 2MnO4（–）+ 10SO4（2–） + 16H（+）

2Mn（2+） + 5NaBiO3 + 14H（+）= 2MnO4（–） +5Bi（3+） + 5Na（+） + 7H2O

(3) Compounds of manganese (IV)

The most important Mn (IV) compound is MnO2, manganese dioxide It is very stable in neutral medium, and tends to transform into manganese (Ⅵ) acid salt in alkaline medium; In acid medium Strong oxidant , tends to be converted into Mn.

2MnO2+2H2SO4 (concentrated)=2MnSO4+O2 ↑+2H2O

MnO2+4HCl (concentrated)=MnCl2+Cl2 ↑+2H2O

Simple Mn (IV) salt aqueous solution Moderately unstable, or hydrolysis Produce hydrated manganese dioxide MnO (OH) 2, or react with water in strong acid to produce oxygen and Mn (II).

(4) Compounds of manganese (VI)

The most important Mn (VI) compounds are Potassium manganate K2MnO4。 stay Molten alkali MnO2 is oxidized by air to K2MnO4.

2MnO2+O2+4KOH=2K2MnO4 (dark green)+2H2O

In acidic, neutral and weakly alkaline media, K2MnO4 happen Disproportionation reaction ：

3K2MnO4 + 2H2O = 2KMnO4 + MnO2 + 4KOH

Potassium manganate Is preparation potassium permanganate (KMnO4) intermediate 。

2MnO4（2–）+ 2H2O=2MnO4 （–）+ 2OH（–）+ H2↑

KMnO4 is a dark purple crystal and a strong oxidant. and reducing agent The product obtained from the reaction is due to the solution acidity Different but different. For example, reaction with SO:

Acidic 2MnO4 (–)+5SO+6H (+)=2Mn (2+)+5SO+3H2O

Near neutral 2MnO4 (–)+3SO+H2O=2MnO2+3 SO+2OH (–)

Alkaline: 2MnO4 (–)+SO+2OH (–)=2MnO4 (2 –)+SO+H2O^[2]

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