Transition metal

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Transition metal

In chemistry

Chemistry

Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions....
, the term transition metal (sometimes also called a transition element) has two possible meanings:

The first definition is simple and has traditionally been used. However, many interesting properties of the transition elements as a group are the result of their partly filled d subshells. Periodic trends in the d-block are less prevailing than in the rest of the periodic table.

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Why do many of the transition elements in period 4 form ion with a 2+ charge?

When was the term "transition element" or "transition metal" first defined? ... and by who.

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In chemistry

Chemistry

It commonly refers to any element in the d-block
D-block

The d-block of the periodic table consists of those periodic table groups that contain elements in which, in the atomic ground state, the highest-energy electron is in a d-atomic orbital....
of the periodic table
Periodic table

The periodic table of the chemical elements is a table method of displaying the chemical elements. Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869....
, including the group 12
Group 12 element

A group 12 element is one of the Chemical element in periodic table group in the periodic table, consisting of zinc , cadmium and Mercury ....
elements zinc
Zinc

Zinc is a metallic chemical element with the symbol Zn and atomic number 30. It is a first-row transition metal of the group 12 element of the periodic table....
, cadmium
Cadmium

Cadmium is a chemical element with the symbol Cd and atomic number 48. A relatively abundant , soft, bluish-white, transition metal, cadmium is known to cause cancer and occurs with zinc ores....
and mercury
Mercury (element)

Mercury , also called quicksilver or hydrargyrum , is a chemical element with the symbol Hg and atomic number 80. A heavy, silvery d-block metal, mercury is one of six elements that are liquid at or near room temperature and pressure....
. This corresponds to groups 3 to 12 on the periodic table
Periodic table

The periodic table of the chemical elements is a table method of displaying the chemical elements. Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869....
, which are all metal
Metal

In chemistry, a metal is a chemical element whose atoms readily lose electrons to form positive ions , and form metallic bonds between other metal atoms and ionic bonds between nonmetal atoms....
s.

More strictly, IUPAC defines a transition metal as "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." By this definition, zinc
Zinc

Zinc is a metallic chemical element with the symbol Zn and atomic number 30. It is a first-row transition metal of the group 12 element of the periodic table....
, cadmium
Cadmium

Cadmium is a chemical element with the symbol Cd and atomic number 48. A relatively abundant , soft, bluish-white, transition metal, cadmium is known to cause cancer and occurs with zinc ores....
, and mercury
Mercury (element)

Mercury , also called quicksilver or hydrargyrum , is a chemical element with the symbol Hg and atomic number 80. A heavy, silvery d-block metal, mercury is one of six elements that are liquid at or near room temperature and pressure....
are excluded from the transition metals, as they have a d¹⁰ configuration
D electron count

The d electron count is a chemistry formalism used to describe the electron configuration of the valence electrons of a transition metal center in a coordination complexes....
. Only a few transient species of these elements that leave ions with a partly filled d subshell have been formed, and mercury(I) only occurs as Hg₂²⁺, which does not strictly form a lone ion with a partly filled subshell, and hence these three elements are inconsistent with the latter definition. They do form ions with a 2+ oxidation state
Oxidation state

In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical Electrical charge that an atom would have if all bonds to atoms of different elements were 100% Ionic bond....
, but these retain the d¹⁰ configuration
D electron count

The d electron count is a chemistry formalism used to describe the electron configuration of the valence electrons of a transition metal center in a coordination complexes....
. Element 112 may also be excluded although its oxidation properties are unlikely to be observed due to its radioactive
Radioactive decay

Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting ionizing particles and radiation. This decay, or loss of energy, results in an atom of one type, called the parent nuclide transforming to an atom of a different type, called the daughter nuclide....
nature. This definition corresponds to groups 3 to 11 on the periodic table.

The first definition is simple and has traditionally been used. However, many interesting properties of the transition elements as a group are the result of their partly filled d subshells. Periodic trends in the d-block are less prevailing than in the rest of the periodic table. Going across a period, the valence

Valence electron

In science, valence electrons are the electrons contained in the outermost, or valence, electron shell of an atom. Valence electrons are important in determining how an chemical element reacts chemically with other elements: The fewer valence electrons an atom holds, the less reactivity it becomes and the more likely it is to chemical rea...
doesn't change, so the electron being added to an atom goes to the inner shell, not outer shell, strengthening the shield.

The (loosely defined) transition metals are the 40 chemical elements 21 to 30, 39 to 48, 71 to 80, and 103 to 112. The name transition comes from their position in the periodic table

Periodic table

The periodic table of the chemical elements is a table method of displaying the chemical elements. Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869....
of elements. In each of the four periods in which they occur, these elements represent the successive addition of electrons to the d atomic orbital

Atomic orbital

An atomic orbital is a mathematical function that describes the wave-like behavior of an electron in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus....
s of the atoms. In this way, the transition metals represent the transition between group 2 elements and group 13 elements.

Variable oxidation states

As opposed to group 1 and group 2 , ions of the transition elements may have multiple oxidation states, since they can lose f electrons without a high energetic penalty. Manganese, for example has two 4s electrons and five 3d electrons, which can be removed. Loss of all of these electrons leads to a +7 oxidation state. Osmium

Osmium

Osmium is a chemical element that has the symbol Os and atomic number 76. Osmium is a hard, brittle, blue-gray or blue-black transition metal in the platinum family, and is the densest natural element....
and ruthenium

Ruthenium

Ruthenium is a chemical element that has the symbol Ru and atomic number 44. A rare transition metal of the platinum group of the periodic table, ruthenium is found associated with platinum ores and used as a catalyst in some platinum alloys....
compounds are commonly found alone in stable +8 oxidation states, which is among the highest for isolatable compounds.

Patterns in oxidation state emerge across the period of transition elements:

The number of oxidation states of each ion increases up to Mn, after which they decrease. Later transition metals have a stronger attraction between proton
Proton

The proton is a subatomic particle with an electric charge of +1 elementary charge. It is found in the nucleus of each atom but is also stable by itself and has a second identity as the hydrogen ion, H+....
s and electron
Electron

The electron is a subatomic particle that carries a negative electric charge. It has elementary particle and is believed to be a point particle....
s (since there are more of each present), which then would require more energy to remove the electrons.

Colored compounds

We observe varying frequencies of electromagnetic radiation in the visible region of the electromagnetic spectrum as colour. Different colours result from the changed energy distribution of photons (light particles) after it has been reflected

Reflection (physics)

Reflection is the change in direction of a wavefront at an wiktionary:interface between two differentmedium so that the wavefront returns into the medium from which it originated....
, transmitted or absorbed

Absorption (electromagnetic radiation)

In physics, absorption of electromagnetic radiation is the way by which the energy of a photon is taken up by matter, typically the electrons of an atom....
after hitting a substance. Because of their structure, transition metals form many different coloured ions and complexes. Colour even varies between the different ions of a single element - MnO₄^- (Mn in oxidation state 7+) is a purple compound, whereas Mn²⁺ is pale-pink.

Coordination by ligand

Ligand

In chemistry, a ligand is either an atom, ion, or molecule that bonds to a central metal, generally involving formal donation of one or more of its electrons....
s can play a part in determining color in a transition compound, due to changes in energy of the d orbitals. Ligand

Ligand

In chemistry, a ligand is either an atom, ion, or molecule that bonds to a central metal, generally involving formal donation of one or more of its electrons....
s remove degeneracy of the orbitals and split them in to higher and lower energy groups. The energy gap between the lower and higher energy orbitals will determine the color of light that is absorbed, as electromagnetic radiation is only absorbed if it has energy corresponding to that gap. When a ligated ion absorbs light, some of the electrons are promoted to a higher energy orbital. Since different frequency light is absorbed, different colors are observed.

The colour of a complex depends on:

the nature of the metal ion, specifically the number of electrons in the d orbitals
the arrangement of the ligands around the metal ion (for example geometric isomers can display different colours)
the nature of the ligands surrounding the metal ion. The stronger the ligands then the greater the energy difference between the split high and low 3d groups.

The complex ion formed by the d-block element zinc (though not strictly a transition element) is colorless, because the 3d orbitals are full - no electrons are able to move up to the higher group.

Transition metal

Variable oxidation states

Colored compounds

See also