Subliminal stimuli

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

Subliminal stimuli (/sʌbˈlɪmɪnəl/; the prefix sub- literally means "below" or "less than") are any sensory stimuli below an individual's threshold for conscious perception, in contrast to supraliminal stimuli (above threshold). A 2012 review of functional magnetic resonance imaging (fMRI) studies showed that subliminal stimuli activate specific regions of the brain despite participants' unawareness. Visual stimuli may be quickly flashed before an individual can process them, or flashed and then masked to interrupt processing. Audio stimuli may be played below audible volumes or masked by other stimuli.

Effectiveness

Applications of subliminal stimuli are often based on the persuasiveness of a message. Research on action priming has shown that subliminal stimuli can only trigger actions a receiver of the message plans to perform anyway. However, consensus of subliminal messaging remains unsubstantiated by other research. Most actions can be triggered subliminally only if the person is already prepared to perform a specific action.

The context that the stimulus is presented in affects their effectiveness. For example, if the target is thirsty then a subliminal stimulus for a drink is likely to influence the target to purchase that drink if it is readily available. The stimuli can also influence the target to choose the primed option over other habitually chosen options. If the subliminal stimuli are for a product that is not quickly accessible or if there is no need for it within a specific context then the stimuli will have little to no effect. Subliminal priming can direct people's actions even when they believe they are making free choices. When primed to push a button with their off-hand, people will use that hand even if they are given a free choice between using their off-hand and their dominant hand. However, a meta analysis of many strong articles displaying effectiveness of subliminal messaging revealed its effects on actual consumer purchasing choices between two alternatives are not statistically significant; subliminal messaging is only effective in very specific contexts.

Method

In subliminal stimuli research, the threshold is the level at which the participant is not aware of the stimulus being presented. Researchers determine a threshold for the stimulus that is used as the subliminal stimulus. That stimulus is then presented during the study at some point and measures are taken to determine the effects of the stimulus. The way in which studies operationally define thresholds depends on the methods of the particular article. The methodology of the research also varies by the type of subliminal stimulus (auditory or visual) and the dependent variables they measure.

Objective threshold

The objective threshold is found using a forced-choice procedure, in which participants must choose which stimulus they saw from options given to them. For example, participants are flashed a stimulus (like the word orange) and then given a few choices and asked which one they saw. Participants must choose an answer in this design. The objective threshold is obtained when participants are at the chance level of performance in this task. The length of presentation that causes chance performance on the forced-choice task is used later in the study for the subliminal stimuli.

Subjective threshold

The subjective threshold is determined when the participant reports that their performance on the forced-choice procedure approximates chance. The subjective threshold is 30 to 50 ms slower than the objective threshold, demonstrating that participants' ability to detect the stimuli is earlier than their perceived accuracy ratings would indicate; that is, stimuli presented at a subjective threshold have a longer presentation time than those presented at an objective threshold. When using the objective threshold, priming stimuli neither facilitated nor inhibited the recognition of a color. However, the longer the duration of the priming stimulus, the greater effect it had on subsequent responding. These findings indicate that the results of some studies may be due to their definition of below threshold.

Direct and indirect measures

Perception without awareness can be demonstrated through the comparison of direct and indirect measures of perception. Direct measures use responses to task definitions in accordance to the explicit instructions given to the subjects, while indirect measures use responses that are not a part of the task definition given to subjects. Both direct and indirect measures are displayed under comparable conditions except for the direct or indirect instruction. For example, in a typical Stroop test, subjects are asked to name the color of a patch of ink. A direct measure is accuracy—true to the instructions given to the participants. The popular indirect measure used in the same task is response time—subjects are not told that they are being measured for response times.

Similarly, a direct effect is the effect of a task stimulus on the instructed response to it, and is usually measured as accuracy. An indirect effect is an uninstructed effect of the task stimulus on behavior, sometimes measured by including an irrelevant or distracting component in the task stimulus and measuring its effect on accuracy. These effects are then compared on their relative sensitivity: an indirect effect that is greater than a direct effect indicates that unconscious cognition exists.

Visual stimuli

In order to study the effects of subliminal stimuli, researchers often prime participants with specific visual stimuli, and determine if those stimuli elicit different responses. Subliminal stimuli have mostly been studied in the context of emotion; in particular, researchers have focused a lot of attention to the face perception and how subliminal presentation to different facial expression affects emotion. Visual subliminal stimuli have also been used to study emotion eliciting stimuli and simple geometric stimuli. A significant amount of research has been produced throughout the years to demonstrate the effects of subliminal visual stimuli.

Images

Attitudes can develop without being aware of their antecedents. Individuals viewed slides of people performing familiar daily activities after being exposed to either an emotionally positive scene, such as a romantic couple or kittens, or an emotionally negative scene, such as a werewolf or a dead body between each slide and the next. After exposure from something which the individuals consciously perceived as a flash of light, the participants exhibited more positive personality traits to those people whose slides were associated with an emotionally positive scene and vice versa. Despite the statistical difference, the subliminal messages had less of an impact on judgment than the slide's inherent level of physical attractiveness.

Individuals show right amygdala activity in response to subliminal fear, and a greater left amygdala response to supraliminal fear. In a 2005 study, participants were exposed to a subliminal image flashed for 16.7 milliseconds that could signal a potential threat and again with a supraliminal image flashed for half a second. Furthermore, supraliminal fear showed more sustained cortical activity, suggesting that subliminal fear may not entail conscious surveillance while supraliminal fear entails higher-order processing.

Emotion eliciting stimuli

A subliminal sexual stimulus has a different effect on men compared to women. In a study by Omri Gilliath et al., men and women were subliminally exposed to either a sexual or a neutral picture, and their sexual arousal was recorded. Researchers examined the accessibility of sex-related thoughts after following the same procedure with either a pictorial judgment task or lexical decision task. The results revealed that the subliminal sexual stimuli did not have an effect on men, but for women, lower levels of sexual arousal were reported. However, in conditions related to accessibility of sex-related thoughts, the subliminal sexual stimuli led to higher accessibility for both men and women.

Subliminal stimuli can elicit significant emotional changes, but these changes are not valuable for a therapeutic effect. Spider-fearful and non-fearful undergraduates experienced either a positive, negative, or neutral subliminal priming stimulus followed immediately by a picture of a spider or a snake. Using visual analogue scales, the participants rated the affective quality of the picture. No evidence was found to support that the unpleasantness of the pictures can be modulated by subliminal priming. Non-fearful participants rated the spiders as being more frightening after being primed with a negative stimulus, but the event was not found in fearful participants.

Simple geometric stimuli

Laboratory research on unconscious perception often employs simple stimuli (e.g., geometric shapes or colors) in which visibility is controlled by visual masking. Masked stimuli are then used to prime the processing of subsequently presented target stimuli. For instance, in the response priming paradigm, participants have to respond to a target stimulus (e.g. by identifying whether it is a diamond or a square) which is immediately preceded by a masked priming stimulus (also a diamond or a square). The prime has large effects on responses to the target: it speeds responses when it is consistent with the target, and slows responses when it is inconsistent. Response priming effects can be dissociated from visual awareness of the prime, such as when prime identification performance is at chance, or when priming effects increase despite decreases in prime visibility.

The presentation of geometric figures as subliminal stimuli can result in below threshold discriminations. The geometric figures were presented on slides of a tachistoscope followed by a supraliminal shock for a given slide every time it appeared. The shock was administered after a five-second interval. Electrical skin changes of the participants that occurred before the reinforcement (shock) or non-reinforcement were recorded. The findings indicate that the proportion of electrical skin changes that occurred following subliminal visual stimuli was significantly greater than expected, while the proportion of electrical skin changes that occurred in response to the stimuli which were not reinforced was significantly less. As a whole, participants were able to make below threshold discriminations.

Word and non-word stimuli

Another form of visual stimuli is words and non-words. In a set of experiments, words and non-words were used as subliminal primes. Priming stimuli that work best as subliminal stimuli are words that have been classified several times before they are used to prime. Word primes can also be made from parts of practiced words to create new words. In this case, the actual word used to prime can have the opposite meaning of the words it came from (its "parents"), but it will still prime for the meaning of the parent words. Non-words created from previously practiced stimuli have a similar effect, even when they are unpronounceable (e.g. made of all consonants). These primes generally only increase response times for later stimuli for a very short period of time (milliseconds).

Masking visual stimuli

Visual stimuli are often masked by forward and backward masks so that they can be displayed for longer periods of time without the subject being able to recognize the priming stimuli. A forward mask is briefly displayed before the priming stimulus and a backward mask usually follows it to prevent the subject from recognizing the stimulus.

Auditory stimuli

Auditory masking

One method for creating subliminal auditory stimuli is masking, which involves hiding the target auditory stimulus in some way. Auditory subliminal stimuli are shown to have some effect on the participant, but not a large one. For example, one study used other speechlike sounds to cover up the target words, and it found evidence of priming in the absence of awareness of the stimuli. The effects of these subliminal stimuli were only seen in one of the outcome measures of priming, while the effects of conscious stimuli were seen in multiple outcome measures. However, the empirical evidence for the assumption of an impact of auditory subliminal stimuli on human behavior remains weak; in an experimental study on the influence of subliminal target words (embedded into a music track) on choice behavior for a drink, authors found no evidence for a manipulative effect.

Self-help audio recordings

A study investigated the effects on self-concept of rational emotive behavior therapy and auditory subliminal stimulation (separately and in combination) on 141 undergraduate students with self-concept problems. They were randomly assigned to one of four groups receiving either rational-emotive therapy, subliminal stimulation, both, or a placebo treatment. Rational-emotive therapy significantly improved scores on all dependent measures (cognition, self-concept, self-esteem, anxiety) except behavior. Results for the subliminal stimulation group were similar to those of the placebo treatment except for a significant self-concept improvement and a decline in self-concept-related irrational cognitions. The combined treatment yielded results similar to those of rational-emotive therapy, with tentative indications of continued improvement in irrational cognitions and self-concept from posttest to follow-up.

Consumption and television

Some studies looked at the efficacy of subliminal messaging in television. Subliminal messages produce only one-tenth of the effects of detected messages and the findings related to the effects of subliminal messaging were relatively ambiguous. Participants’ ratings of positive responses to commercials were not affected by subliminal messages in the commercials.

Johan Karremans suggests that subliminal messages have an effect when the messages are goal-relevant. In a study, researchers made half of the 105 volunteers feel thirsty by giving them food with lots of salt before performing the experiment. At the end, as predicted, they found that the subliminal message had succeeded among the thirsty. 80% of them chose a certain ice tea brand versus the 20% of the control group that were not exposed to the message. Those who were not thirsty did not choose the drink in question, despite the subliminal message. The experiment showed that in certain circumstances subliminal advertising worked.

Karremans did a study assessing whether subliminal priming of a brand name of a drink would affect a person's choice of drink, and if this effect was caused by the individual's feelings of being thirsty. In another study, participant's ratings of thirst were higher after viewing an episode of The Simpsons that contained single frames of the word thirsty or of a picture of a Coca-Cola can. Some studies showed greater effects of subliminal messaging with as high as 80% of participants showing a preference for a particular rum when subliminally primed by the name placed in an ad backward. Martin Gardner, however, criticizes claims, such as those by Wilson Bryan Key, by pointing out that "recent studies" serving as the basis for his claims were not identified by place or experimenter. He also suggests that claims about subliminal images are due to the "tendency of chaotic shapes to form patterns vaguely resembling familiar things". In 2009, the American Psychological Association defended that subliminal stimuli are subordinated to previously structured associative stimuli and that their only role is to reinforce a certain behavior or a certain previous attitude, without there being conclusive evidence that the stimulus that provokes these behaviors is properly subliminal.

Currently, there is still speculation about this effect. Many authors have continued to argue for the effectiveness of subliminal cues in changing consumption behavior, citing environmental cues as a main culprit of behavior change. Authors who support this line of reasoning cite findings such as Ronald Millman's research that showed slow-paced music in a supermarket was associated with more sales and customers moving at a slower pace. Findings such as these support the notion that external cues can affect behavior, although the stimulus may not fit into a strict definition of subliminal stimuli because although the music may not be attended to or consciously affecting the customers, they are certainly able to perceive it.

Subliminal messaging is prohibited in advertising in the United Kingdom.

Studies on advertising with subliminal stimuli in still images

Among the researchers in favor of subliminal stimuli is Wilson Bryan Key. One of Key's most cited studies is a whisky ad in which he found several hidden figures in ice cubes. However, Cecil Adams wrote that Key is someone with a sexual fixation.

Luís Bassat suggests an interesting observation by indicating that the current objective of advertising is "to get the consumer to take into account the brand when making the decision", a trend opposed to the objective of subliminal advertising. In turn, Fernando Ocaña showed that the essential thing in the field of media planning is to obtain the greatest possible memory, which implies a conscious perception and not an unconscious one as it should be the case.

Boron group

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

 

Boron group (group 13)
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson group 12 ←    → carbon group
IUPAC group number 13 Name by element boron group Trivial name triels CAS group number (US, pattern A-B-A) IIIA old IUPAC number (Europe, pattern A-B) IIIB
↓ Period
2	Boron (B) 5 Metalloid
3	Aluminium (Al) 13 Other metal
4	Gallium (Ga) 31 Other metal
5	Indium (In) 49 Other metal
6	Thallium (Tl) 81 Other metal
7	Nihonium (Nh) 113 other metal
Legend primordial element synthetic element Atomic number color: black=solid

The boron group are the chemical elements in group 13 of the periodic table, comprising boron (B), aluminium (Al), gallium (Ga), indium (In), thallium (Tl), and perhaps also the chemically uncharacterized nihonium (Nh). The elements in the boron group are characterized by having three valence electrons. These elements have also been referred to as the triels.

Boron is commonly classified as a (metalloid) while the rest, with the possible exception of nihonium, are considered post-transition metals. Boron occurs sparsely, probably because bombardment by the subatomic particles produced from natural radioactivity disrupts its nuclei. Aluminium occurs widely on earth, and indeed is the third most abundant element in the Earth's crust (8.3%). Gallium is found in the earth with an abundance of 13 ppm. Indium is the 61st most abundant element in the earth's crust, and thallium is found in moderate amounts throughout the planet. Nihonium is not known to occur in nature and therefore is termed a synthetic element.

Several group 13 elements have biological roles in the ecosystem. Boron is a trace element in humans and is essential for some plants. Lack of boron can lead to stunted plant growth, while an excess can also cause harm by inhibiting growth. Aluminium has neither a biological role nor significant toxicity and is considered safe. Indium and gallium can stimulate metabolism; gallium is credited with the ability to bind itself to iron proteins. Thallium is highly toxic, interfering with the function of numerous vital enzymes, and has seen use as a pesticide.

Characteristics

Like other groups, the members of this family show patterns in electron configuration, especially in the outermost shells, resulting in trends in chemical behavior:

Z	Element	No. of electrons per shell
5	boron	2, 3
13	aluminium	2, 8, 3
31	gallium	2, 8, 18, 3
49	indium	2, 8, 18, 18, 3
81	thallium	2, 8, 18, 32, 18, 3
113	nihonium	2, 8, 18, 32, 32, 18, 3 (predicted)

The boron group is notable for trends in the electron configuration, as shown above, and in some of its elements' characteristics. Boron differs from the other group members in its hardness, refractivity and reluctance to participate in metallic bonding. An example of a trend in reactivity is boron's tendency to form reactive compounds with hydrogen.

Although situated in p-block, the group is notorious for violation of the octet rule by its members boron and (to a lesser extent) aluminium. All members of the group are characterized as trivalent.

Chemical reactivity

Hydrides

Most of the elements in the boron group show increasing reactivity as the elements get heavier in atomic mass and higher in atomic number. Boron, the first element in the group, is generally unreactive with many elements except at high temperatures, although it is capable of forming many compounds with hydrogen, sometimes called boranes. The simplest borane is diborane, or B₂H₆. Another example is B₁₀H₁₄.

The next group-13 elements, aluminium and gallium, form fewer stable hydrides, although both AlH₃ and GaH₃ exist. Indium, the next element in the group, is not known to form many hydrides, except in complex compounds such as the phosphine complex H₃InP(Cy)₃. No stable compound of thallium and hydrogen has been synthesized in any laboratory.

Oxides

All of the boron-group elements are known to form a trivalent oxide, with two atoms of the element bonded covalently with three atoms of oxygen. These elements show a trend of increasing pH (from acidic to basic). Boron oxide (B₂O₃) is slightly acidic, aluminium and gallium oxide (Al₂O₃ and Ga₂O₃ respectively) are amphoteric, indium(III) oxide (In₂O₃) is nearly amphoteric, and thallium(III) oxide (Tl₂O₃) is a Lewis base because it dissolves in acids to form salts. Each of these compounds are stable, but thallium oxide decomposes at temperatures higher than 875 °C.

A powdered sample of boron trioxide (B₂O₃), one of the oxides of boron

Halides

The elements in group 13 are also capable of forming stable compounds with the halogens, usually with the formula MX₃ (where M is a boron-group element and X is a halogen.) Fluorine, the first halogen, is able to form stable compounds with every element that has been tested (except neon and helium), and the boron group is no exception. It is even hypothesized that nihonium could form a compound with fluorine, NhF₃, before spontaneously decaying due to nihonium's radioactivity. Chlorine also forms stable compounds with all of the elements in the boron group, including thallium, and is hypothesized to react with nihonium. All of the elements will react with bromine under the right conditions, as with the other halogens but less vigorously than either chlorine or fluorine. Iodine will react with all natural elements in the periodic table except for the noble gases, and is notable for its explosive reaction with aluminium to form 2AlI₃. Astatine, the heaviest halogen, has only formed a few compounds, due to its radioactivity and short half-life, and no reports of a compound with an At–Al, –Ga, –In, –Tl, or –Nh bond have been seen, although scientists think that it should form salts with metals.

Physical properties

It has been noticed that the elements in the boron group have similar physical properties, although most of boron's are exceptional. For example, all of the elements in the boron group, except for boron itself, are soft. Moreover, all of the other elements in group 13 are relatively reactive at moderate temperatures, while boron's reactivity only becomes comparable at very high temperatures. One characteristic that all do have in common is having three electrons in their valence shells. Boron, being a metalloid, is a thermal and electrical insulator at room temperature, but a good conductor of heat and electricity at high temperatures. Unlike boron, the metals in the group are good conductors under normal conditions. This is in accordance with the long-standing generalization that all metals conduct heat and electricity better than most non-metals.

Oxidation states

The inert s-pair effect is significant in the group-13 elements, especially the heavier ones like thallium. This results in a variety of oxidation states. In the lighter elements, the +3 state is the most stable, but the +1 state becomes more prevalent with increasing atomic number, and is the most stable for thallium. Boron is capable of forming compounds with lower oxidization states, of +1 or +2, and aluminium can do the same. Gallium can form compounds with the oxidation states +1, +2 and +3. Indium is like gallium, but its +1 compounds are more stable than those of the lighter elements. The strength of the inert-pair effect is maximal in thallium, which is generally only stable in the oxidation state of +1, although the +3 state is seen in some compounds. Stable and monomeric gallium, indium and thallium radicals with a formal oxidation state of +2 have since been reported. Nihonium may have +5 oxidation state.

Periodic trends

There are several trends that one could notice as they look at the properties of Boron group members. The Boiling Points of these elements drop from period to period, while densities tend to rise.

The 5 stable elements of the boron group

 

Element	Boiling Point	Density (g/cm3)
Boron	4,000°C	2.46
Aluminium	2,519°C	2.7
Gallium	2,204°C	5.904
Indium	2,072°C	7.31
Thallium	1,473°C	11.85

Nuclear

With the exception of the synthetic nihonium, all of the elements of the boron group have stable isotopes. Because all their atomic numbers are odd, boron, gallium and thallium have only two stable isotopes, while aluminium and indium are monoisotopic, having only one, although most indium found in nature is the weakly radioactive ¹¹⁵In. ¹⁰B and ¹¹B are both stable, as are ²⁷Al, ⁶⁹Ga and ⁷¹Ga, ¹¹³In, and ²⁰³Tl and ²⁰⁵Tl. All of these isotopes are readily found in macroscopic quantities in nature. In theory, though, all isotopes with an atomic number greater than 66 are supposed to be unstable to alpha decay. Conversely, all elements with atomic numbers are less than or equal to 66 (except Tc, Pm, Sm and Eu) have at least one isotope that is theoretically energetically stable to all forms of decay (with the exception of proton decay, which has never been observed, and spontaneous fission, which is theoretically possible for elements with atomic numbers greater than 40).

Like all other elements, the elements of the boron group have radioactive isotopes, either found in trace quantities in nature or produced synthetically. The longest-lived of these unstable isotopes is the indium isotope ¹¹⁵In, with its extremely long half-life of 4.41 × 10¹⁴ y. This isotope makes up the vast majority of all naturally occurring indium despite its slight radioactivity. The shortest-lived is ⁷B, with a half-life of a mere 350±50 × 10⁻²⁴ s, being the boron isotope with the fewest neutrons and a half-life long enough to measure. Some radioisotopes have important roles in scientific research; a few are used in the production of goods for commercial use or, more rarely, as a component of finished products.

History

The boron group has had many names over the years. According to former conventions it was Group IIIB in the European naming system and Group IIIA in the American. The group has also gained two collective names, "earth metals" and "triels". The latter name is derived from the Latin prefix tri- ("three") and refers to the three valence electrons that all of these elements, without exception, have in their valence shells. The name "triels" was first suggested by International Union of Pure and Applied Chemistry (IUPAC) in 1970.

Boron was known to the ancient Egyptians, but only in the mineral borax. The metalloid element was not known in its pure form until 1808, when Humphry Davy was able to extract it by the method of electrolysis. Davy devised an experiment in which he dissolved a boron-containing compound in water and sent an electric current through it, causing the elements of the compound to separate into their pure states. To produce larger quantities he shifted from electrolysis to reduction with sodium. Davy named the element boracium. At the same time two French chemists, Joseph Louis Gay-Lussac and Louis Jacques Thénard, used iron to reduce boric acid. The boron they produced was oxidized to boron oxide. Aluminium, like boron, was first known in minerals before it was finally extracted from alum, a common mineral in some areas of the world. Antoine Lavoisier and Humphry Davy had each separately tried to extract it. Although neither succeeded, Davy had given the metal its current name. It was only in 1825 that the Danish scientist Hans Christian Ørsted successfully prepared a rather impure form of the element. Many improvements followed, a significant advance being made just two years later by Friedrich Wöhler, whose slightly modified procedure still yielded an impure product. The first pure sample of aluminium is credited to Henri Etienne Sainte-Claire Deville, who substituted sodium for potassium in the procedure. At that time aluminium was considered precious, and it was displayed next to such metals as gold and silver. The method used today, electrolysis of aluminium oxide dissolved in cryolite, was developed by Charles Martin Hall and Paul Héroult in the late 1880s.

The mineral zinc blende, more commonly known as sphalerite, in which indium can occur.

Thallium, the heaviest stable element in the boron group, was discovered by William Crookes and Claude-Auguste Lamy in 1861. Unlike gallium and indium, thallium had not been predicted by Dmitri Mendeleev, having been discovered before Mendeleev invented the periodic table. As a result, no one was really looking for it until the 1850s when Crookes and Lamy were examining residues from sulfuric acid production. In the spectra they saw a completely new line, a streak of deep green, which Crookes named after the Greek word θαλλός (thallos), referring to a green shoot or twig. Lamy was able to produce larger amounts of the new metal and determined most of its chemical and physical properties.

Indium is the fourth element of the boron group but was discovered before the third, gallium, and after the fifth, thallium. In 1863 Ferdinand Reich and his assistant, Hieronymous Theodor Richter, were looking in a sample of the mineral zinc blende, also known as sphalerite (ZnS), for the spectroscopic lines of the newly discovered element thallium. Reich heated the ore in a coil of platinum metal and observed the lines that appeared in a spectroscope. Instead of the green thallium lines that he expected, he saw a new line of deep indigo-blue. Concluding that it must come from a new element, they named it after the characteristic indigo color it had produced.

Gallium minerals were not known before August 1875, when the element itself was discovered. It was one of the elements that the inventor of the periodic table, Dmitri Mendeleev, had predicted to exist six years earlier. While examining the spectroscopic lines in zinc blende the French chemist Paul Emile Lecoq de Boisbaudran found indications of a new element in the ore. In just three months he was able to produce a sample, which he purified by dissolving it in a potassium hydroxide (KOH) solution and sending an electric current through it. The next month he presented his findings to the French Academy of Sciences, naming the new element after the Greek name for Gaul, modern France.

The last confirmed element in the boron group, nihonium, was not discovered but rather created or synthesized. The element's synthesis was first reported by the Dubna Joint Institute for Nuclear Research team in Russia and the Lawrence Livermore National Laboratory in the United States, though it was the Dubna team who successfully conducted the experiment in August 2003. Nihonium was discovered in the decay chain of moscovium, which produced a few precious atoms of nihonium. The results were published in January of the following year. Since then around 13 atoms have been synthesized and various isotopes characterized. However, their results did not meet the stringent criteria for being counted as a discovery, and it was the later RIKEN experiments of 2004 aimed at directly synthesizing nihonium that were acknowledged by IUPAC as the discovery.

Etymology

The name "boron" comes from the Arabic word for the mineral borax,(بورق, boraq) which was known before boron was ever extracted. The "-on" suffix is thought to have been taken from "carbon". Aluminium was named by Humphry Davy in the early 1800s. It is derived from the Greek word alumen, meaning bitter salt, or the Latin alum, the mineral. Gallium is derived from the Latin Gallia, referring to France, the place of its discovery. Indium comes from the Latin word indicum, meaning indigo dye, and refers to the element's prominent indigo spectroscopic line. Thallium, like indium, is named after the Greek word for the color of its spectroscopic line: thallos, meaning a green twig or shoot."Nihonium" is named after Japan (Nihon in Japanese), where it was discovered.

Occurrence and abundance

Boron

Boron, with its atomic number of 5, is a very light element. Almost never found free in nature, it is very low in abundance, composing only 0.001% (10 ppm) of the Earth's crust. It is known to occur in over a hundred different minerals and ores, however: the main source is borax, but it is also found in colemanite, boracite, kernite, tusionite, berborite and fluoborite. Major world miners and extractors of boron include Turkey, the United States, Argentina, China, Bolivia and Peru. Turkey is by far the most prominent of these, accounting for around 70% of all boron extraction in the world. The United States is second, most of its yield coming from the state of California.

Aluminium

Aluminium, in contrast to boron, is the most abundant metal in the Earth's crust, and the third most abundant element. It composes about 8.2% (82,000 ppm) of the Earth’s crust, surpassed only by oxygen and silicon. It is like boron, however, in that it is uncommon in nature as a free element. This is due to aluminium's tendency to attract oxygen atoms, forming several aluminium oxides. Aluminium is now known to occur in nearly as many minerals as boron, including garnets, turquoises and beryls, but the main source is the ore bauxite. The world's leading countries in the extraction of aluminium are Ghana, Surinam, Russia and Indonesia, followed by Australia, Guinea and Brazil.

Gallium

Gallium is a relatively rare element in the Earth's crust and is not found in as many minerals as its lighter homologues. Its abundance on the Earth is a mere 0.0018% (18 ppm). Its production is very low compared to other elements, but has increased greatly over the years as extraction methods have improved. Gallium can be found as a trace in a variety of ores, including bauxite and sphalerite, and in such minerals as diaspore and germanite. Trace amounts have been found in coal as well. The gallium content is greater in a few minerals, including gallite (CuGaS₂), but these are too rare to be counted as major sources and make negligible contributions to the world's supply.

Indium

Indium is another rare element in the boron group. Even less abundant than gallium at only 0.000005% (0.05 ppm), it is the 61st most common element in the earth's crust. Very few indium-containing minerals are known, all of them scarce: an example is indite. Indium is found in several zinc ores, but only in minute quantities; likewise some copper and lead ores contain traces. As is the case for most other elements found in ores and minerals, the indium extraction process has become more efficient in recent years, ultimately leading to larger yields. Canada is the world's leader in indium reserves, but both the United States and China have comparable amounts.

Thallium

A small bundle of fiberglass

Thallium is of intermediate abundance in the Earth's crust, estimated to be 0.00006% (0.6 ppm). Thallium is the 56th most common element in the earth's crust, more abundant than indium by a sizeable amount. It is found on the ground in some rocks, in the soil and in clay. Many sulfide ores of iron, zinc and cobalt contain thallium. In minerals it is found in moderate quantities: some examples are crookesite (in which it was first discovered), lorandite, routhierite, bukovite, hutchinsonite and sabatierite. There are other minerals that contain small amounts of thallium, but they are very rare and do not serve as primary sources.

Nihonium

Nihonium is an element that is never found in nature but has been created in a laboratory. It is therefore classified as a synthetic element with no stable isotopes.

Applications

With the exception of synthetic nihonium, all the elements in the boron group have numerous uses and applications in the production and content of many items.

Boron

Main article: Boron § Applications

Boron has found many industrial applications in recent decades, and new ones are still being found. A common application is in fiberglass. There has been rapid expansion in the market for borosilicate glass; most notable among its special qualities is a much greater resistance to thermal expansion than regular glass. Another commercially expanding use of boron and its derivatives is in ceramics. Several boron compounds, especially the oxides, have unique and valuable properties that have led to their substitution for other materials that are less useful. Boron may be found in pots, vases, plates, and ceramic pan-handles for its insulating properties.

The compound borax is used in bleaches, for both clothes and teeth. The hardness of boron and some of its compounds give it a wide array of additional uses. A small part (5%) of the boron produced finds use in agriculture.

Aluminium

Main article: Aluminium § Applications

Aluminium is a metal with numerous familiar uses in everyday life. It is most often encountered in construction materials, in electrical devices, especially as the conductor in cables, and in tools and vessels for cooking and preserving food. Aluminium's lack of reactivity with food products makes it particularly useful for canning. Its high affinity for oxygen makes it a powerful reducing agent. Finely powdered pure aluminium oxidizes rapidly in air, generating a huge amount of heat in the process (burning at about 5500 °F or 3037 °C), leading to applications in welding and elsewhere that a large amount of heat is needed. Aluminium is a component of alloys used for making lightweight bodies for aircraft. Cars also sometimes incorporate aluminium in their framework and body, and there are similar applications in military equipment. Less common uses include components of decorations and some guitars. The element is also sees use in a diverse range of electronics.

Gallium is one of the chief components of blue LEDs

Gallium

Main article: Gallium § Applications

Gallium and its derivatives have only found applications in recent decades. Gallium arsenide has been used in semiconductors, in amplifiers, in solar cells (for example in satellites) and in tunnel diodes for FM transmitter circuits. Gallium alloys are used mostly for dental purposes. Gallium ammonium chloride is used for the leads in transistors. A major application of gallium is in LED lighting. The pure element has been used as a dopant in semiconductors, and has additional uses in electronic devices with other elements. Gallium has the property of being able to 'wet' glass and porcelain, and thus can be used to make mirrors and other highly reflective objects. Gallium can be added to alloys of other metals to lower their melting points.

Indium

Main article: Indium § Applications

Indium's uses can be divided into four categories: the largest part (70%) of the production is used for coatings, usually combined as indium tin oxide (ITO); a smaller portion (12%) goes into alloys and solders; a similar amount is used in electrical components and in semiconductors; and the final 6% goes to minor applications. Among the items in which indium may be found are platings, bearings, display devices, heat reflectors, phosphors, and nuclear control rods. Indium tin oxide has found a wide range of applications, including glass coatings, solar panels, streetlights, electrophosetic displays (EPDs), electroluminescent displays (ELDs), plasma display panels (PDPs), electrochemic displays (ECs), field emission displays (FEDs), sodium lamps, windshield glass and cathode ray tubes, making it the single most important indium compound.

Thallium

Main article: Thallium § Applications

Thallium is used in its elemental form more often than the other boron-group elements. Uncompounded thallium is used in low-melting glasses, photoelectric cells, switches, mercury alloys for low-range glass thermometers, and thallium salts. It can be found in lamps and electronics, and is also used in myocardial imaging. The possibility of using thallium in semiconductors has been researched, and it is a known catalyst in organic synthesis. Thallium hydroxide (TlOH) is used mainly in the production of other thallium compounds. Thallium sulfate (Tl₂SO₄) is an outstanding vermin-killer, and it is a principal component in some rat and mouse poisons. However, the United States and some European countries have banned the substance because of its high toxicity to humans. In other countries, though, the market for the substance is growing. Tl₂SO₄ is also used in optical systems.

Biological role

None of the group-13 elements has a major biological role in complex animals, but some are at least associated with a living being. As in other groups, the lighter elements usually have more biological roles than the heavier. The heaviest ones are toxic, as are the other elements in the same periods. Boron is essential in most plants, whose cells use it for such purposes as strengthening cell walls. It is found in humans, certainly as a essential trace element, but there is ongoing debate over its significance in human nutrition. Boron's chemistry does allow it to form complexes with such important molecules as carbohydrates, so it is plausible that it could be of greater use in the human body than previously thought. Boron has also been shown to be able to replace iron in some of its functions, particularly in the healing of wounds. Aluminium has no known biological role in plants or animals, despite its widespread occurrence in nature. Gallium is not essential for the human body, but its relation to iron(III) allows it to become bound to proteins that transport and store iron. Gallium can also stimulate metabolism. Indium and its heavier homologues have no biological role, although indium salts in small doses, like gallium, can stimulate metabolism.

Toxicity

All of the elements in the boron group can be toxic, given a high enough dose. Some of them are only toxic to plants, some only to animals, and some to both.

As an example of boron toxicity, it has been observed to harm barley in concentrations exceeding 20 mM. The symptoms of boron toxicity are numerous in plants, complicating research: they include reduced cell division, decreased shoot and root growth, decreased production of leaf chlorophyll, inhibition of photosynthesis, lowering of stomata conductance, reduced proton extrusion from roots, and deposition of lignin and suborgin.

Aluminium does not present a prominent toxicity hazard in small quantities, but very large doses are slightly toxic. Gallium is not considered toxic, although it may have some minor effects. Indium is not toxic and can be handled with nearly the same precautions as gallium, but some of its compounds are slightly to moderately toxic.

Thallium, unlike gallium and indium, is extremely toxic, and has caused many poisoning deaths. Its most noticeable effect, apparent even from tiny doses, is hair loss all over the body, but it causes a wide range of other symptoms, disrupting and eventually halting the functions of many organs. The nearly colorless, odorless and tasteless nature of thallium compounds has led to their use by murderers. The incidence of thallium poisoning, intentional and accidental, increased when thallium (with its similarly toxic compound, thallium sulfate) was introduced to control rats and other pests. The use of thallium pesticides has therefore been prohibited since 1975 in many countries, including the USA.

Nihonium is a highly unstable element and decays by emitting alpha particles. Due to its strong radioactivity, it would definitely be extremely toxic, although significant quantities of nihonium (larger than a few atoms) have not yet been assembled.