Transition elements areperiodic table of ele mentsChemical elements from Group IIIB to Group V III (in some places, all elements of the auxiliary group and Group VIII are included in the scope of transition elements).These elements areatomThe common structural features arevalence electronSuccessively filled in the secondary outer layerD TrackTherefore, sometimes people alsoLanthanideandActinide elementIncluded in the transition elements.Because the elements of Group IB (copper, silver, gold) also use d electrons in the formation of+2 and+3 valence compounds;Group IIB elements (zinc, cadmium, mercury) are stable in formationCoordination compoundIt is similar to the traditional transition elements in terms of ability. Therefore, I B and II B elements are often included in the transition elements.
Chinese name
Transitional element
Foreign name
transition elements
Alias
transition metal
atomic configuration
There are only 1~2 electrons in the outermost layer
Elements in the periodic table from IIIB to VIII.There are three series of elements (scandium to nickelyttriumreachpalladiumandlanthanumreachplatinum）The electrons fill their 3d, 4d and 5d orbits one by one.Sometimes people expand the scope of transition elements to include lanthanides and actinides.So sometimesCopper group elementIncluded in the scope of transition elements.Zinc group element(IIB) Stable formationCoordination compoundAbility and transitionelementIt is very similar, so it is also suggested that zinc group elements should be included in the scope of transition elements.And of each series of transition elementsAz radiusIt decreases slowly from left to right, and the radius of elements of each family increases slightly from top to bottom, but it is not likeMain familyThe element increases so significantly.
General introduction
The transition element is located in the middle of the periodic table, and the electrons in the d or f sublayer of the atom are not filled.These elements are metals, also known astransition metal。According to the characteristics of electronic structure, transition elements can be divided into external transition elements (also called d zone elements) andInner transition element(also known asElement of zone f）Two groups.
External transition elements include lanthanum, actinide and other transition elements except lanthanide and actinide. Their d orbitals are not fully filled with electrons, and their f orbitals are completely empty (four or five cycles) or full (sixth cycle).
Inner transition elementLanthanide and actinide elements whose electronic parts are filled into the f orbital.
The transition elements in zone d can be divided into three series according to the period of the element:
① Sc ～ Ni ----- in the fourth period of the periodic table is called the first transition system element.
② The Y~Pd in the fifth cycle is called the second transition system element.
③ La ～ Pt in the sixth cycle is called the third transition system element.
Characteristics
The characteristics and properties of transition elements are as follows: ① They are metals with high melting point, high boiling point, high hardness, high density, etcMetallic luster，Ductility、ConductivityandThermal conductivityAll are very good, and various alloys can be formed between different transition metals. ②transition metalThere may be a single d electron in the atom or ion ofspinDetermines the magnetism of atoms or molecules.Therefore, many transition metals haveParamagnetism，iron, cobalt and nickel can also be observedFerromagnetism。Can be used asmagnetic material 。③ D electrons of transition elements occurchemical reactionAll the timeChemical bondThe formation ofOxidized state。Highest oxidation stateFrom scandiumyttrium、lanthanumFrom+3 to+8 for ruthenium and osmium.When transition elements form low oxidation compounds, they generally form ionic bonds and are easy to formhydrate；In the formation of highly oxidized compoundscovalent bond。④Transition elementHydrated ionIn compounds or solutions, most of them show a certain color, which is due to the unsaturated or irregular electronic layer structure. ⑤Transition elements have empty d orbitals that can be used for bonding and high charges/Radius ratio, are easy to communicate with variousLigandsForm stableCoordination compound。Most transition metals have their own unique production methods:electrolysisMethod, metal thermal reduction methodHydrogen reductionandIodideThermal decomposition method.[1]
atomic structure
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atomic configuration
The electronic configuration of transition element atoms is characterized by that their d orbitals are not full of electrons (except Pd), the outermost layer has only 1-2 electrons, and their valence electron configuration is (n-1) done-9ns1-2(Pd is 4d5s).
Note: The crossed line indicates a relatively common and stable oxidation state;Brackets indicate unstable oxidation state.
The changes of atomic orbital energy of multi electron atoms are relatively complex, because there areEnergy level interleavingThe energy difference between energy levels is small, so in many reactions, the d electrons of transition elements can participate in bonding partially or completely.
Atomic radius
The atomic radius of transition elements is smaller than that of elements of group IA and IIA in the same period.
The atomic radius decreases with the increase of atomic number in each period, and increases before and after the copper subgroup.
From top to bottom in all ethnic groupsAtomic radiusHowever, the atomic radius of the fifth and sixth period homologous elements is very close, and the atomic radius of hafnium (146 pm) is almost the same as that of zirconium (146 pm).
The electrons in the d orbital of the transition element with the same period are not full, the shielding effect of the d electron is small, the nuclear charge increases in turn, and the attraction to the outer electrons increases, so the atomic radius decreases in turn.Before and after the copper sub group, the filled d orbitals enhance the shielding effect and increase the atomic radius.becauseLanthanide shrinkageThe atomic radii of the elements of the same family in the fifth and sixth periods are similar.
Ionic radiusThe change law is similar to the change of atomic radius, that is, the same period from left to right, the same ionic radius of oxidation state gradually decreases with the increase of nuclear charge;The ion radius of the highest oxidation state of the same group elements increases with the increase of the number of electron layers from top to bottom;The lanthanide contraction effect also affects the ion radius of the fifth and sixth cycle homologous elements.[2]
Nature comparison
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physical property
① Transition elements generally have smallerAtomic radius, both the outermost s electron and the secondary d electron can participate in the formationMetal bondTo increase the strength of the key.
③ Except scandium and titanium, the rest are heavy metals.
④ Most transition elements have higher melting points and boiling points, as well as higher hardness and density.For example, tungsten is the most difficult metal to melt, and chromium is the hardest metal.
chemical property
① The metallicity of transition elements is stronger than that of p elements in the same period, but weaker than that of s elements in the same period.
② The elements in the first transition system are more active than those in the second and third transition systems - nuclear charge and atomic radius.
In the same family, the atomic radius increases slightly from top to bottom, but the nuclear charge increases more, which increases the attraction to the outer electrons, and the nuclear charge plays a leading roleCompared with the elements in the second transition system, the atomic radius of the elements in the third transition system increases little（Lanthanide shrinkageSo its chemical properties are more inactive.
The first transition system can generally replace hydrogen from dilute acid (hydrochloric acid and sulfuric acid)Electrode potentialBasically, the value increases gradually from left to right, which is consistent with the gradual weakening of metallicity.
There are some exceptions to the value of manganese (lower than that of chromium): the loss of two 4s electrons forms a stable 3d configuration.
Scandium, yttrium and lanthanum are the most active metals in the transition elements. They can be rapidly oxidized in air, and react with water to release hydrogen, which can also be dissolved in acid. This is because they have only one electron in the secondary outer d orbital, which is easy to lose, so their properties are more active and close toalkaline-earth metal。[3]
Relevant information
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Oxidized state
The outermost s electron and the second outer d electron of the transition element can participate in bonding, so the transition element often has a variety of oxidation states.Generally, it can be increased from+Ⅱ to the oxidation state with the same number of groups (except Ru and Os, other elements of Group Ⅷ B have no+Ⅷ oxidation state).
In the same cycle, from left to right, the oxidation state first gradually increases, and then gradually decreases.
With 3d trackNumber of electronsThe oxidation state increased with the increase of;When the number of electrons in the 3d orbit reaches 5 or more, the 3d orbit gradually tends to be stable, and the high oxidation state gradually becomes unstable (showing strong oxidation), and then the oxidation state gradually decreases.
The change trend of the oxidation state of the three transition system elements is consistent from left to right.The difference is that the highest oxidation state of the elements in the second and third transition systems is stable, while the low oxidation state compounds are not common.
In the same family, from top to bottom, the high oxidation state tends to be relatively stable ----- andMain family elementsDifferent.
To explain how life appeared on the earth is like answering the paradox of chicken or egg: how do basic biochemical substances such as amino acids and nucleotidesBiocatalyst(protein or ribozyme) completed its construction before its appearance?In the latest issue of Biology Bulletin, scientists published a paper pointing out that the third type of catalyst activated metabolism and life in deep-sea hot springs.
according toGeorge Mason University The model proposed by Harold Molowitz, Salas Srinivasan in Vega, and Eric Smith of the Santa Fe Institute includesTransition metal elementsThe molecular structure of (iron, copper, nickel, etc.) and ligands (small organic molecules) can catalyze the synthesis of basic biochemical substances (monomers).Monomers are the basic building blocks of more complex molecules, which ultimately led to the origin of life.
Molowitz said that in the past 50 years, there has been a big problem in the theoretical research of the origin of life, that is, "you need big protein molecules as catalysts to form monomers, but you need monomers to make catalysts".To solve this problem, Molowitz proposed that we can start with these small metal ligand catalysts to produce monomers used to form large protein catalysts.
Transition metal atoms, as the core of metal ligand complexes, must be surrounded by other ligands.Molowitz and his colleagues proposed that simple transition metal ligand complexes in deep-sea hot springs can catalyze reactions that produce more complex molecules.Later, these increasingly complex molecules play the role of ligands in the transition metal ligand complex catalysts with increasing efficiency.Gradually accumulated the basic molecular components of metabolism, and self-organized the chemical reaction network that laid the foundation of life.
Molowitz said: "We once thought that if we knew what carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur were doing, we would understand biology. However, we found that there are some other rare elements transition metals are also necessary in biology, so we must ask what role they played in the origin of life?"Morovitz is listing the elements that make up most of the biomass on the earth.
Researchers point out that the emergence of life forms is the natural result of the uniqueness of transition metals and ligand field theory, which describes the characteristics of ligand complexes.Morovitz said: "This idea originated fromperiodic table of ele mentsResearch.We strongly feel that unless you can see how life appears in some chemical way, you can never really solve this problem. "
Molowitz and his colleagues are preparing to use experimental methods to test the catalytic performance of transition metal ligand complexes made of different ligands.Ligands are known to bind tightly to transition metals, including molecules produced in the tricarboxylic acid cycle (a series of biochemical reactions necessary for many microorganisms).Morovitz said that they believed that life began with the tricarboxylic acid cycle, and there was evidence that there were circulating intermediates formed in the environment of deep-sea hot springs.Scientists plan to mix these intermediate molecules with different transition metals, heat them to different temperatures and maintain them for a corresponding period of time, and then check what kind of catalyst will be produced.
Such experiments are expected to help us understand what kind of catalytic reaction happens when we lay the foundation of life.The hypothesis also suggests that life may appear more than once.Researchers say that life may have multiple origins. If life can be found elsewhere in the universe, these life and human life may be very similar, because they are based on the same basis as human beingstransition metalAnd ligands.This is just a guess, but it may become the core idea of the origin of life research.[4]
