Youth

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Youth 

A group of college women in the United States, 1973. The term adolescence is often considered synonymous with youth.

 

Young people dressed in casual wear attend Woodstock Festival of rock music, Poland, 2011

 

A group of youth in Sweden 2019.

Youth is the time of life when one is young, and often means the time between childhood and adulthood (maturity). It is also defined as "the appearance, freshness, vigor, spirit, etc., characteristic of one who is young". Its definitions of a specific age range varies, as youth is not defined chronologically as a stage that can be tied to specific age ranges; nor can its end point be linked to specific activities, such as taking unpaid work or having sexual relations.

Youth is an experience that may shape an individual's level of dependency, which can be marked in various ways according to different cultural perspectives. Personal experience is marked by an individual's cultural norms or traditions, while a youth's level of dependency means the extent to which they still rely on their family emotionally and economically.

Terminology and definitions

Students of a U.S. university do an outdoor class, where they discuss topics while walking.

 

Youth in Afghanistan

General

Around the world, the English terms youth, adolescent, teenager, kid, youngster and young person are interchanged, often meaning the same thing, but they are occasionally differentiated. Youth can be referred to as the time of life when one is young. This involves childhood, and the time of life which is neither childhood nor adulthood, but rather somewhere in between. Youth also identifies a particular mindset of attitude, as in "He is very youthful". For certain uses, such as employment statistics, the term also sometimes refers to individuals from the ages of 14 to 21. However, the term adolescence refers to a specific age range during a specific developmental period in a person's life, unlike youth which is a socially constructed category.

The United Nations defines youth as persons between the ages of roughly 15 and 24 with all UN statistics based on this range, the UN states education as a source for these statistics. The UN also recognizes that this varies without prejudice to other age groups listed by member states such as 18–30. A useful distinction within the UN itself can be made between teenagers (i.e. those between the ages of 13 and 19) and young adults (those between the ages of 20 and 29). While seeking to impose some uniformity on statistical approaches, the UN itself is aware of contradictions between approaches in its own statutes. Hence under the 15–24 definition (introduced in 1981) children are defined as those under the age of 14 (someone 13 and younger) while under the 1979 Convention on the Rights of the Child, those under the age of 18 are regarded as children. The UN also states they are aware that several definitions exist for youth within UN entities such as Youth Habitat 15–32, NCSL 12-24, and African Youth Charter 15–35.

On November 11, 2020, the State Duma of the Russian Federation approved a project to raise the cap on the age of young people from 30 to 35 years (the range now extending from 14 to 35 years).

Although linked to biological processes of development and aging, youth is also defined as a social position that reflects the meanings different cultures and societies give to individuals between childhood and adulthood. The term in itself when referred to in a manner of social position can be ambiguous when applied to someone of an older age with very low social position; potentially when still dependent on their guardians. Scholars argue that age-based definitions have not been consistent across cultures or times and that thus it is more accurate to focus on social processes in the transition to adult independence for defining youth.

"This world demands the qualities of youth: not a time of life but a state of mind, a temper of the will, a quality of imagination, a predominance of courage over timidity, of the appetite for adventure over the life of ease." – Robert Kennedy

Youth is the stage of constructing the self-concept. The self-concept of youth is influenced by variables such as peers, lifestyle, gender, and culture. It is a time of a person's life when their choices are most likely to affect their future.

Other definitions

Youth skateboarding in Mexico

 

Students of Peru discuss agricultural issues.

In much of sub-Saharan Africa, the term "youth" is associated with young men from 12 to 30 or 35 years of age. Youth in Nigeria includes all members of the Federal Republic of Nigeria aged 18–35. Many African girls experience youth as a brief interlude between the onset of puberty and marriage and motherhood. But in urban settings, poor women are often considered youth much longer, even if they bear children outside of marriage. Varying culturally, the gender constructions of youth in Latin America and Southeast Asia differ from those of sub-Saharan Africa. In Vietnam, widespread notions of youth are sociopolitical constructions for both sexes between the ages of 15 and 35.

In Brazil, the term youth refers to people of both sexes from 15 to 29 years old. This age bracket reflects the influence on Brazilian law of international organizations like the World Health Organization (WHO). It is also shaped by the notion of adolescence that has entered everyday life in Brazil through a discourse on children's rights.

The OECD defines youth as "those between 15 and 29 years of age".

August 12 was declared International Youth Day by the United Nations.

Youth rights

Main article: Youth rights

Children's rights cover all the rights that belong to children. When they grow up they are granted with new rights (like voting, consent, driving, etc.) and duties (criminal response, etc.). There are different minimum limits of age at which youth are not free, independent or legally competent to take some decisions or actions. Some of these limits are: voting age, age of candidacy, age of consent, age of majority, age of criminal responsibility, drinking age, driving age, etc. After youth reach these limits they are free to vote, have sexual intercourse, buy or consume alcoholic beverages or drive cars, etc.

Voting age

Main article: Voting age

Voting age is the minimum age established by law that a person must attain to be eligible to vote in a public election. Typically, the age is set at 18 years; however, ages as low as 16 and as high as 21 exist (see list below). Studies show that 21% of all 18-year-olds have experience with voting. This is an important right since, by voting, they can support politics selected by themselves and not only by people of older generations.

Age of candidacy

Main article: Age of candidacy

Age of candidacy is the minimum age at which a person can legally qualify to hold certain elected government offices. In many cases, it also determines the age at which a person may be eligible to stand for an election or be granted ballot access.

Age of consent

Main article: Age of consent

The age of consent is the age at which a person is considered legally competent to consent to sexual acts, and is thus the minimum age of a person with whom another person is legally permitted to engage in sexual activity. The distinguishing aspect of the age of consent laws is that the person below the minimum age is regarded as the victim, and their sex partner as the offender.

Defense of infancy

Main article: Defense of infancy

The defense of infancy is a form of defense known as an excuse so that defendants falling within the definition of an "infant" are excluded from criminal liability for their actions, if at the relevant time, they had not reached an age of criminal responsibility. This implies that children lack the judgment that comes with age and experience to be held criminally responsible. After reaching the initial age, there may be levels of responsibility dictated by age and the type of offense committed.

Drinking age

Main article: Drinking age

The legal drinking age is the age at which a person can consume or purchase alcoholic beverages. These laws cover a wide range of issues and behaviors, addressing when and where alcohol can be consumed. The minimum age alcohol can be legally consumed can be different from the age when it can be purchased in some countries. These laws vary among different countries and many laws have exemptions or special circumstances. Most laws apply only to drinking alcohol in public places, with alcohol consumption in the home being mostly unregulated (an exception being the UK, which has a minimum legal age of five for supervised consumption in private places). Some countries also have different age limits for different types of alcoholic drinks.

Driving age

Main article: Driving age

Driving age is the age at which a person can apply for a driver's license. Countries with the lowest driving ages (below 17) are Argentina, Australia, Canada, El Salvador, Iceland, Israel, Estonia, Macedonia, Malaysia, New Zealand, Norway, the Philippines, Russia, Saudi Arabia, Slovenia, Sweden, the United Kingdom (Mainland) and the United States. The Canadian province of Alberta and several U.S. states permit youth driving as low as 14. Niger has the highest minimum driving age in the world at 23. In India, driving is legal after getting a license at the age of 18.

Legal working age

Main article: Legal working age

See also: Right to work

The legal working age is the minimum age required by law for a person to work in each country or jurisdiction. The threshold of adulthood, or "the age of majority" as recognized or declared in law in most countries, has been set at age 18. Some types of labor are commonly prohibited even for those above the working age, if they have not reached the age of majority. Activities that are dangerous, harmful to the health or that may affect the morals of minors fall into this category.

Student rights in higher education

Main article: Student rights in higher education

Student rights are those rights, such as civil, constitutional, contractual and consumer rights, which regulate student rights and freedoms and allow students to make use of their educational investment. These include such things as the right to free speech and association, to due process, equality, autonomy, safety and privacy, and accountability in contracts and advertising, which regulate the treatment of students by teachers and administrators.

Smoking age

Main article: Smoking age

The smoking age is the minimum age a person can buy tobacco and/or smoke in public. Most countries regulate this law at the national level while at some point it is done by the state or province.

School and education

Main article: Schooling

Young people spend much of their lives in educational settings, and their experiences in schools, colleges and universities can shape much of their subsequent lives. Research shows that poverty and income affect the likelihood for the incompletion of high school. These factors also increase the likelihood for the youth to not go to a college or university. In the United States, 12.3 percent of young people ages 16 to 24 are disconnected, meaning they are neither in school nor working.

Health and mortality

Youths in South Africa partying

The leading causes of morbidity and mortality among youth and adults are due to certain health-risk behaviors. These behaviors are often established during youth and extend into adulthood. Since the risk behaviors in adulthood and youth are interrelated, problems in adulthood are preventable by influencing youth behavior.

A 2004 mortality study of youth (defined in this study as ages 10–24) mortality worldwide found that 97% of deaths occurred in low to middle-income countries, with the majority in southeast Asia and sub-Saharan Africa. Maternal conditions accounted for 15% of female deaths, while HIV/AIDS and tuberculosis were responsible for 11% of deaths; 14% of male and 5% of female deaths were attributed to traffic accidents, the largest cause overall. Violence accounted for 12% of male deaths. Suicide was the cause of 6% of all deaths.

The U.S. Centers for Disease Control and Prevention developed its Youth Risk Behavior Surveillance System (YRBSS) in 2003 to help assess risk behavior. YRBSS monitors six categories of priority health-risk behaviors among youth and young adults. These are behaviors that contribute to unintentional injuries and violence;

• tobacco, alcohol and other drug use;
• sexual behaviors that contribute to unintended pregnancy and sexually transmitted diseases (STDs), including human immunodeficiency virus (HIV) infection;
• unhealthy dietary behaviors;
• physical inactivity—plus overweight.

YRBSS includes a national school-based survey conducted by CDC as well as state and local school-based surveys conducted by education and health agencies.

Universal school-based interventions such as formal classroom curricula, behavioural management practices, role‐play, and goal‐setting may be effective in preventing tobacco use, alcohol use, illicit drug use, antisocial behaviour, and improving physical activity of young people.

Obesity

Main article: Childhood obesity

Obesity now affects one in five children in the United States, and is the most prevalent nutritional disease of children and adolescents in the United States. Although obesity-associated morbidities occur more frequently in adults, significant consequences of obesity as well as the antecedents of adult disease occur in obese children and adolescents.

Discrimination against overweight children begins early in childhood and becomes progressively institutionalized. Obese children may be taller than their non-overweight peers, in which case they are apt to be viewed as more mature. The inappropriate expectations that result may have an adverse effect on their socialization.

Many of the cardiovascular consequences that characterize adult-onset obesity are preceded by abnormalities that begin in childhood. Hyperlipidemia, hypertension, and abnormal glucose tolerance occur with increased frequency in obese children and adolescents. The relationship of cardiovascular risk factors to visceral fat independent of total body fat remains unclear. Sleep apnea, pseudotumor cerebri, and Blount's disease represent major sources of morbidity for which rapid and sustained weight reduction is essential. Although several periods of increased risk appear in childhood, it is not clear whether obesity with onset early in childhood carries a greater risk of adult morbidity and mortality.

Bullying

Bullying among school-aged youth is increasingly being recognized as an important problem affecting well-being and social functioning. While a certain amount of conflict and harassment is typical of youth peer relations, bullying presents a potentially more serious threat to healthy youth development. The definition of bullying is widely agreed on in literature on bullying.

Bullying often happens in schools

The majority of research on bullying has been conducted in Europe and Australia. Considerable variability among countries in the prevalence of bullying has been reported. In an international survey of adolescent health-related behaviors, the percentage of students who reported being bullied at least once during the current term ranged from a low of 15% to 20% in some countries to a high of 70% in others. Of particular concern is frequent bullying, typically defined as bullying that occurs once a week or more. The prevalence of frequent bullying reported internationally ranges from a low of 1.9% among one Irish sample to a high of 19% in a Malta study.

Research examining characteristics of youth involved in bullying has consistently found that both bullies and those bullied demonstrate poorer psychosocial functioning than their non-involved peers. Youth who bully others tend to demonstrate higher levels of conduct problems and dislike of school, whereas youth who are bullied generally show higher levels of insecurity, anxiety, depression, loneliness, unhappiness, physical and mental symptoms, and low self-esteem. Males who are bullied also tend to be physically weaker than males in general. The few studies that have examined the characteristics of youth who both bully and are bullied found that these individuals exhibit the poorest psychosocial functioning overall.

See also: School bullying

Sexual health and politics

General

Globalization and transnational flows have had tangible effects on sexual relations, identities, and subjectivities. In the wake of an increasingly globalized world order under waning Western dominance, within ideologies of modernity, civilization, and programs for social improvement, discourses on population control, 'safe sex', and 'sexual rights'. Sex education programmes grounded in evidence-based approaches are a cornerstone in reducing adolescent sexual risk behaviours and promoting sexual health. In addition to providing accurate information about consequences of Sexually transmitted disease or STIs and early pregnancy, such programmes build life skills for interpersonal communication and decision making. Such programmes are most commonly implemented in schools, which reach large numbers of teenagers in areas where school enrollment rates are high. However, since not all young people are in school, sex education programmes have also been implemented in clinics, juvenile detention centers and youth-oriented community agencies. Notably, some programmes have been found to reduce risky sexual behaviours when implemented in both school and community settings with only minor modifications to the curricula.

Philippines

The Sangguniang Kabataan ("Youth Council" in English), commonly known as SK, was a youth council in each barangay (village or district) in the Philippines, before being put "on hold", but not quite abolished, prior to the 2013 barangay elections. The council represented teenagers from 15 to 17 years old who have resided in their barangay for at least six months and registered to vote. It was the local youth legislature in the village and therefore led the local youth program and projects of the government. The Sangguniang Kabataan was an offshoot of the KB or the Kabataang Barangay (Village Youth) which was abolished when the Local Government Code of 1991 was enacted.

In the Global South

The vast majority of young people live in developing countries: according to the United Nations, globally around 85 per cent of 15- to 24-year-olds live in developing countries, a figure projected to grow 89.5 per cent by 2025. Moreover, this majority are extremely diverse: some live in rural areas but many inhabit the overcrowded metropolises of India, Mongolia and other parts of Asia and in South America, some live traditional lives in tribal societies, while others participate in global youth culture in ghetto contexts.

Many young lives in developing countries are defined by poverty, some suffer from famine and a lack of clean water, while involvement in armed conflict is all common. Health problems are rife, especially due to the prevalence of HIV/AIDS in certain regions. The United Nations estimates that 200 million young people live in poverty, 130 million are illiterate and 10 million live with HIV/AIDS.

Transition metal

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Transition_metal 

In chemistry, the term transition metal (or transition element) has three possible definitions:

• The IUPAC definition defines a transition metal as "an element whose atom has a partially filled d sub-shell, or which can give rise to cations with an incomplete d sub-shell".
• Many scientists describe a "transition metal" as any element in the d-block of the periodic table, which includes groups 3 to 12 on the periodic table. In actual practice, the f-block lanthanide and actinide series are also considered transition metals and are called "inner transition metals".
• Cotton and Wilkinson expand the brief IUPAC definition (see above) by specifying which elements are included. As well as the elements of groups 4 to 11, they add scandium and yttrium in group 3, which have a partially filled d sub-shell in the metallic state. Lanthanum and actinium, which they consider group 3 elements, are however classified as lanthanides and actinides respectively.

English chemist Charles Rugeley Bury (1890–1968) first used the word transition in this context in 1921, when he referred to a transition series of elements during the change of an inner layer of electrons (for example n = 3 in the 4th row of the periodic table) from a stable group of 8 to one of 18, or from 18 to 32. These elements are now known as the d-block.

The first row of transition metals in order.

Classification

In the d-block, the atoms of the elements have between zero and ten d electrons.

Transition metals in the d-block

Group	3	4	5	6	7	8	9	10	11	12
Period 4	21Sc	22Ti	23V	24Cr	25Mn	26Fe	27Co	28Ni	29Cu	30Zn
5	39Y	40Zr	41Nb	42Mo	43Tc	44Ru	45Rh	46Pd	47Ag	48Cd
6	71Lu	72Hf	73Ta	74W	75Re	76Os	77Ir	78Pt	79Au	80Hg
7	103Lr	104Rf	105Db	106Sg	107Bh	108Hs	109Mt	110Ds	111Rg	112Cn

The elements of groups 4–11 are generally recognized as transition metals, justified by their typical chemistry, i.e. a large range of complex ions in various oxidation states, coloured complexes, and catalytic properties either as the element or as ions (or both). Sc and Y in group 3 are also generally recognized as transition metals. However, the elements La–Lu and Ac–Lr and group 12 attract different definitions from different authors.

1. Many chemistry textbooks and printed periodic tables classify La and Ac as group 3 elements and transition metals, since their atomic ground-state configurations are s²d¹ like Sc and Y. The elements Ce–Lu are considered as the "lanthanide" series (or "lanthanoid" according to IUPAC) and Th–Lr as the "actinide" series. The two series together are classified as f-block elements, or (in older sources) as "inner transition elements". However, this results in a split of the d-block into two quite uneven portions.
2. Some inorganic chemistry textbooks include La with the lanthanides and Ac with the actinides. This classification is based on similarities in chemical behaviour (though this similarity mostly only exists among the lanthanides) and defines 15 elements in each of the two series, even though they correspond to the filling of an f sub-shell, which can only contain 14 electrons.
3. A third classification defines the f-block elements as La–Yb and Ac–No, while placing Lu and Lr in group 3. This is based on the Aufbau principle (or Madelung rule) for filling electron sub-shells, in which 4f is filled before 5d (and 5f before 6d), so that the f sub-shell is actually full at Yb (and No), while Lu has an [ ]s²f¹⁴d¹ configuration. (Lr is an exception where the d-electron is replaced by a p-electron, but the energy difference is small enough that in a chemical environment it often displays d-occupancy anyway.) La and Ac are, in this view, simply considered exceptions to the Aufbau principle with electron configuration [ ]s²d¹ (not [ ]s²f¹ as the Aufbau principle predicts). Excited states for the free atom and ion can become the ground state in chemical environments, which justifies this interpretation; La and Ac have vacant low-lying f sub-shells which are filled in Lu and Lr, so excitation to f orbitals is possible in La and Ac but not in Lu or Lr. This justifies the idea that La and Ac simply have irregular configurations (similar to Th as s²d²), and that they are the real beginning of the f-block.

As the third form is the only form that allows simultaneous (1) preservation of the sequence of increasing atomic numbers, (2) a 14-element-wide f-block, and (3) avoidance of the split in the d-block, it has been suggested by a 2021 IUPAC preliminary report as the preferred form. Such a modification, treating Lu as a transition element rather than as an inner transition element, was first suggested by Soviet physicists Lev Landau and Evgeny Lifshitz in 1948. Following this, it was then suggested by many other physicists and chemists, and was generally the classification adopted by those who considered the issue, but textbooks generally lagged in adopting it.

Zinc, cadmium, and mercury are sometimes excluded from the transition metals, as they have the electronic configuration [ ]d¹⁰s², with no incomplete d shell. In the oxidation state +2, the ions have the electronic configuration [ ]…d¹⁰. Although these elements can exist in other oxidation states, including the +1 oxidation state, as in the diatomic ion Hg²⁺
₂, they still have a complete d shell in these oxidation states. The group 12 elements Zn, Cd and Hg may therefore, under certain criteria, be classed as post-transition metals in this case. However, it is often convenient to include these elements in a discussion of the transition elements. For example, when discussing the crystal field stabilization energy of first-row transition elements, it is convenient to also include the elements calcium and zinc, as both Ca²⁺
and Zn²⁺
have a value of zero, against which the value for other transition metal ions may be compared. Another example occurs in the Irving–Williams series of stability constants of complexes.

The recent (though disputed and so far not reproduced independently) synthesis of mercury(IV) fluoride (HgF
₄) has been taken by some to reinforce the view that the group 12 elements should be considered transition metals, but some authors still consider this compound to be exceptional. Copernicium is expected to be able to use its d-electrons for chemistry as its 6d sub-shell is destabilised by strong relativistic effects due to its very high atomic number, and as such is expected to have transition-metal-like behaviour when it shows higher oxidation states than +2 (which are not definitely known for the lighter group 12 elements).

Although meitnerium, darmstadtium, and roentgenium are within the d-block and are expected to behave as transition metals analogous to their lighter congeners iridium, platinum, and gold, this has not yet been experimentally confirmed. Whether copernicium behaves more like mercury or has properties more similar to those of the noble gas radon is not clear.

Subclasses

Early transition metals are on the left side of the periodic table from group 3 to group 7. Late transition metals are on the right side of the d-block, from group 8 to 11 (and 12 if it is counted as transition metals).

Electronic configuration

Main article: Electron configuration

The general electronic configuration of the d-block elements is (noble gas) (n − 1)d^1–10ns^0–2. Here "(noble gas)" is the configuration of the last noble gas preceding the atom in question, and n is the highest principal quantum number of an occupied orbital in that atom. For example Ti(Z = 22) is in period 4 so that n = 4, the first 18 electrons have the same configuration of Ar at the end of period 3, and the overall configuration is (Ar)3d²4s². The period 6 and 7 transition metals also add core (n − 2)f¹⁴ electrons, which are omitted from the tables below. The single exception is lawrencium, which has a 7p occupancy due to relativistic effects that become important at such high Z (though the p-orbitals can also contribute to chemical bonding in lighter transition elements).

The Madelung rule predicts that the inner d orbital is filled after the valence-shell s orbital. The typical electronic structure of transition metal atoms is then written as (noble gas) ns²(n − 1)d^m. This rule is however only approximate – it only holds for some of the transition elements, and only then in the neutral ground states.

The d sub-shell is the next-to-last sub-shell and is denoted as ${\displaystyle (n-1)d}$ sub-shell. The number of s electrons in the outermost s sub-shell is generally one or two except palladium (Pd), with no electron in that s sub shell in its ground state. The s sub-shell in the valence shell is represented as the ns sub-shell, e.g. 4s. In the periodic table, the transition metals are present in eight groups (4 to 11), with some authors including some elements in groups 3 or 12.

The elements in group 3 have an ns²(n − 1)d¹ configuration, except for lawrencium (Lr): its 7s²7p¹ configuration exceptionally does not fill the 6d orbitals at all. The first transition series is present in the 4th period, and starts after Ca (Z = 20) of group-2 with the configuration [Ar]4s², or scandium (Sc), the first element of group 3 with atomic number Z = 21 and configuration [Ar]4s²3d¹, depending on the definition used. As we move from left to right, electrons are added to the same d sub-shell till it is complete. The element of group 11 in the first transition series is copper (Cu) with an atypical configuration [Ar]4s¹3d¹⁰. Despite the filled d sub-shell in metallic copper it nevertheless forms a stable ion with an incomplete d sub-shell. Since the electrons added fill the ${\displaystyle (n-1)d}$ orbitals, the properties of the d-block elements are quite different from those of s and p block elements in which the filling occurs either in s or in p-orbitals of the valence shell. The electronic configuration of the individual elements present in all the d-block series are given below:

First (3d) d-block Series (Sc–Zn)

Group	3	4	5	6	7	8	9	10	11	12
Atomic number	21	22	23	24	25	26	27	28	29	30
Element	Sc	Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn
Electron configuration	3d14s2	3d24s2	3d34s2	3d54s1	3d54s2	3d64s2	3d74s2	3d84s2	3d104s1	3d104s2

Second (4d) d-block Series (Y–Cd)

Atomic number	39	40	41	42	43	44	45	46	47	48
Element	Y	Zr	Nb	Mo	Tc	Ru	Rh	Pd	Ag	Cd
Electron configuration	4d15s2	4d25s2	4d45s1	4d55s1	4d55s2	4d75s1	4d85s1	4d105s0	4d105s1	4d105s2

Third (5d) d-block Series (Lu–Hg)

Atomic number	71	72	73	74	75	76	77	78	79	80
Element	Lu	Hf	Ta	W	Re	Os	Ir	Pt	Au	Hg
Electron configuration	5d16s2	5d26s2	5d36s2	5d46s2	5d56s2	5d66s2	5d76s2	5d96s1	5d106s1	5d106s2

Fourth (6d) d-block Series (Lr–Cn)

Atomic number	103	104	105	106	107	108	109	110	111	112
Element	Lr	Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg	Cn
Electron configuration	7s27p1	6d27s2	6d37s2	6d47s2	6d57s2	6d67s2	6d77s2	6d87s2	6d97s2	6d107s2

A careful look at the electronic configuration of the elements reveals that there are certain exceptions to the Madelung rule. For Cr as an example the rule predicts the configuration 3d⁴4s², but the observed atomic spectra show that the real ground state is 3d⁵4s¹. To explain such exceptions, it is necessary to consider the effects of increasing nuclear charge on the orbital energies, as well as the electron-electron interactions including both coulomb repulsion and exchange energy.

The ${\displaystyle (n-1)d}$ orbitals that are involved in the transition metals are very significant because they influence such properties as magnetic character, variable oxidation states, formation of coloured compounds etc. The valence ${\displaystyle s(ns)}$ and ${\displaystyle p(np)}$ orbitals have very little contribution in this regard since they hardly change in the moving from left to the right in a transition series. In transition metals, there is a greater horizontal similarities in the properties of the elements in a period in comparison to the periods in which the d-orbitals are not involved. This is because in a transition series, the valence shell electronic configuration of the elements do not change. However, there are some group similarities as well.

Characteristic properties

There are a number of properties shared by the transition elements that are not found in other elements, which results from the partially filled d shell. These include

• the formation of compounds whose colour is due to d–d electronic transitions
• the formation of compounds in many oxidation states, due to the relatively low energy gap between different possible oxidation states
• the formation of many paramagnetic compounds due to the presence of unpaired d electrons. A few compounds of main-group elements are also paramagnetic (e.g. nitric oxide, oxygen)

Most transition metals can be bound to a variety of ligands, allowing for a wide variety of transition metal complexes.

Coloured compounds

From left to right, aqueous solutions of: Co(NO
₃)
₂ (red); K
₂Cr
₂O
₇ (orange); K
₂CrO
₄ (yellow); NiCl
₂ (turquoise); CuSO
₄ (blue); KMnO
₄ (purple).

Colour in transition-series metal compounds is generally due to electronic transitions of two principal types.

• charge transfer transitions. An electron may jump from a predominantly ligand orbital to a predominantly metal orbital, giving rise to a ligand-to-metal charge-transfer (LMCT) transition. These can most easily occur when the metal is in a high oxidation state. For example, the colour of chromate, dichromate and permanganate ions is due to LMCT transitions. Another example is that mercuric iodide, HgI₂, is red because of a LMCT transition.

A metal-to-ligand charge transfer (MLCT) transition will be most likely when the metal is in a low oxidation state and the ligand is easily reduced.

In general charge transfer transitions result in more intense colours than d-d transitions.

• d-d transitions. An electron jumps from one d-orbital to another. In complexes of the transition metals the d orbitals do not all have the same energy. The pattern of splitting of the d orbitals can be calculated using crystal field theory. The extent of the splitting depends on the particular metal, its oxidation state and the nature of the ligands. The actual energy levels are shown on Tanabe–Sugano diagrams.

In centrosymmetric complexes, such as octahedral complexes, d-d transitions are forbidden by the Laporte rule and only occur because of vibronic coupling in which a molecular vibration occurs together with a d-d transition. Tetrahedral complexes have somewhat more intense colour because mixing d and p orbitals is possible when there is no centre of symmetry, so transitions are not pure d-d transitions. The molar absorptivity (ε) of bands caused by d-d transitions are relatively low, roughly in the range 5-500 M⁻¹cm⁻¹ (where M = mol dm⁻³). Some d-d transitions are spin forbidden. An example occurs in octahedral, high-spin complexes of manganese(II), which has a d⁵ configuration in which all five electron has parallel spins; the colour of such complexes is much weaker than in complexes with spin-allowed transitions. Many compounds of manganese(II) appear almost colourless. The spectrum of [Mn(H
₂O)
₆]²⁺
shows a maximum molar absorptivity of about 0.04 M⁻¹cm⁻¹ in the visible spectrum.

Oxidation states

A characteristic of transition metals is that they exhibit two or more oxidation states, usually differing by one. For example, compounds of vanadium are known in all oxidation states between −1, such as [V(CO)
₆]⁻
, and +5, such as VO³⁻
₄.

Oxidation states of the transition metals. The solid dots show common oxidation states, and the hollow dots show possible but unlikely states.

Main-group elements in groups 13 to 18 also exhibit multiple oxidation states. The "common" oxidation states of these elements typically differ by two instead of one. For example, compounds of gallium in oxidation states +1 and +3 exist in which there is a single gallium atom. Compounds of Ga(II) would have an unpaired electron and would behave as a free radical and generally be destroyed rapidly, but some stable radicals of Ga(II) are known. Gallium also has a formal oxidation state of +2 in dimeric compounds, such as [Ga
₂Cl
₆]²⁻
, which contain a Ga-Ga bond formed from the unpaired electron on each Ga atom. Thus the main difference in oxidation states, between transition elements and other elements is that oxidation states are known in which there is a single atom of the element and one or more unpaired electrons.

The maximum oxidation state in the first row transition metals is equal to the number of valence electrons from titanium (+4) up to manganese (+7), but decreases in the later elements. In the second row, the maximum occurs with ruthenium (+8), and in the third row, the maximum occurs with iridium (+9). In compounds such as [MnO
₄]⁻
and OsO
₄, the elements achieve a stable configuration by covalent bonding.

The lowest oxidation states are exhibited in metal carbonyl complexes such as Cr(CO)
₆ (oxidation state zero) and [Fe(CO)
₄]²⁻
(oxidation state −2) in which the 18-electron rule is obeyed. These complexes are also covalent.

Ionic compounds are mostly formed with oxidation states +2 and +3. In aqueous solution, the ions are hydrated by (usually) six water molecules arranged octahedrally.

Magnetism

Main article: Magnetochemistry

Transition metal compounds are paramagnetic when they have one or more unpaired d electrons. In octahedral complexes with between four and seven d electrons both high spin and low spin states are possible. Tetrahedral transition metal complexes such as [FeCl
₄]²⁻
are high spin because the crystal field splitting is small so that the energy to be gained by virtue of the electrons being in lower energy orbitals is always less than the energy needed to pair up the spins. Some compounds are diamagnetic. These include octahedral, low-spin, d⁶ and square-planar d⁸ complexes. In these cases, crystal field splitting is such that all the electrons are paired up.

Ferromagnetism occurs when individual atoms are paramagnetic and the spin vectors are aligned parallel to each other in a crystalline material. Metallic iron and the alloy alnico are examples of ferromagnetic materials involving transition metals. Anti-ferromagnetism is another example of a magnetic property arising from a particular alignment of individual spins in the solid state.

Catalytic properties

The transition metals and their compounds are known for their homogeneous and heterogeneous catalytic activity. This activity is ascribed to their ability to adopt multiple oxidation states and to form complexes. Vanadium(V) oxide (in the contact process), finely divided iron (in the Haber process), and nickel (in catalytic hydrogenation) are some of the examples. Catalysts at a solid surface (nanomaterial-based catalysts) involve the formation of bonds between reactant molecules and atoms of the surface of the catalyst (first row transition metals utilize 3d and 4s electrons for bonding). This has the effect of increasing the concentration of the reactants at the catalyst surface and also weakening of the bonds in the reacting molecules (the activation energy is lowered). Also because the transition metal ions can change their oxidation states, they become more effective as catalysts.

An interesting type of catalysis occurs when the products of a reaction catalyse the reaction producing more catalyst (autocatalysis). One example is the reaction of oxalic acid with acidified potassium permanganate (or manganate (VII)). Once a little Mn²⁺ has been produced, it can react with MnO₄⁻ forming Mn³⁺. This then reacts with C₂O₄⁻ ions forming Mn²⁺ again.

Physical properties

As implied by the name, all transition metals are metals and thus conductors of electricity.

In general, transition metals possess a high density and high melting points and boiling points. These properties are due to metallic bonding by delocalized d electrons, leading to cohesion which increases with the number of shared electrons. However the group 12 metals have much lower melting and boiling points since their full d sub-shells prevent d–d bonding, which again tends to differentiate them from the accepted transition metals. Mercury has a melting point of −38.83 °C (−37.89 °F) and is a liquid at room temperature.