Chemical formula: I2
State at room temperature: solid
Molecular weight: 253.8
Element iodine is a purple-black crystal with a density of 4.93g/cm3. The relative atomic mass of element 53 (proton number 53) is 126.9. Melting point 1 13.5℃, boiling point 184.35℃. Valence-1,+1, +3, +5 and +7. The ionization energy is 10.4438+0 eV. It has metallic luster, brittle nature and easy sublimation. Toxic and corrosive. Soluble in organic solvents such as ether, ethanol, chloroform, etc., also soluble in hydroiodic acid and potassium iodide solution, dark brown. It can directly combine with most elements, but it is not as violent as other halogens. Typical organic reactions of iodine include: electrophilic substitution of aromatic compounds to form aryl iodine; Iodization of carbonyl functional groups adjacent to carbon atoms; Addition reaction of iodine (I) on unsaturated hydrocarbon multiple bonds. But it is difficult to dissolve in water. Due to disproportionation, the brown solution is acidic. In aqueous solution, strong reducing agent is needed to reduce iodine (I-). Iodine turns blue when it meets starch.
Iodine is a purple-black shiny solid. Iodine is heated and sublimated into beautiful purple steam with a pungent smell. Iodine can form compounds with most elements, but it is not as active as other halogens (F, Cl, Br). Halogens before iodine can replace iodine from iodide. Iodine has metal-like properties. Iodine is easily soluble in chloroform, carbon tetrachloride, carbon disulfide and other organic solvents to form a beautiful purple solution, but slightly soluble in water (but if there are iodine ions in water, the solubility will increase: (I-)+(I2)==(I3-)). Iodine compounds are very important in organic chemistry and are widely used in medicine and photography. Iodine deficiency can lead to goiter. Excessive iodine can also cause goiter. Iodine will be dark blue when it meets starch, which is one of the characteristics of iodine. Like halogen gas, iodine vapor is toxic, so when taking iodine, try to operate in a fume hood.
Iodine is mainly used to make drugs, dyes, iodine wine, test paper and iodine compounds. Iodine is a medicine made of iodine, potassium iodide and ethanol. It is a reddish-brown transparent liquid with special odor of iodine and ethanol.
Atomic volume: 25.74 ml/mol
Chemical bond energy: (kJ/mol)
Interstate 299
Interstate 228
Interstate 234
I-F 280
I-Cl 208
I-I 15 1
I-Si 234
I 184
Cell parameters:
a = 7 18.02 pm
b = 47 1.02 pm
c = 98 1.03 pm
α = 90
β = 90
γ = 90
Period: 5
Number of families: VIIA
Electron layer arrangement: 2-8- 18- 18-7.
Crystal structure: the unit cells are orthogonal.
Common valence:-1,+1, +3, +5, +7.
Ionization energy (kJ/mol)
M - M+ 1008.4
M+ - M2+ 1845.9
M2+ - M3+ 3200
M3+ - M4+ 4 100
M4+ - M5+ 5000
M5+ - M6+ 7400
M6+ - M7+ 8700
M7+ - M8+ 16400
M8+ - M9+ 19300
M9+ - M 10+ 22 100
[Edit this paragraph] Element content:
Pacific water surface 0.043ppm；; Content in the crust:1.4ppm.
The abundance of iodine in nature is not large, but everything contains iodine, whether it is hard clods or rocks, even the purest transparent crystals contain quite a lot of iodine atoms. Seawater contains a lot of iodine, soil and tap water also contain a lot of iodine, and animals, plants and human bodies contain more iodine.
Seaweed in nature, saltpeter in Chile and mineral water in oil-producing areas also contain high iodine. In industrial production, elemental iodine is produced by adding sodium bisulfite to the mother liquor of seaweed ash or Chilean saltpeter and reducing it.
Related chemical formula:
I2+Fe=FeI2
2KI+Cl2=2KCl+I2
2KI+Br2=2KBr+I2
I2+2NaOH=NaI+NaIO+H2O
3I2+6NaOH=5NaI+NaIO3+3H2O
I2+H2O = Hi +HIO
5Cl2+I2+6H2O=2HIO3+ 10HCl
[Edit this paragraph] The role of iodine in chemistry
Iodine can be used to verify whether a substance contains starch.
Dropping a drop of iodine on the biscuit shows that the iodine is dark blue, indicating that the biscuit contains starch (starch is a kind of polysaccharide).
[Edit this paragraph] found that:
18 1 1 year, iodine was found in the mother liquor of seaweed ash when it was treated with sulfuric acid in Kurt.
/kloc-at the end of 0/8/kloc-at the beginning of 0/9, the French emperor Napoleon launched a war and needed a lot of potassium nitrate to make gunpowder. At that time, courtois, a saltpeter merchant and pharmacist in Dijon, France, used seaweed or seaweed ash solution to convert natural sodium nitrate or other nitrates into potassium nitrate, thus producing potassium nitrate. In 18 1 1, he found that the copper container containing algae ash solution was corroded quickly. He thought that the algae ash solution contained an unknown substance that interacted with copper, so he studied it.
He poured sulfuric acid into the algae ash solution and found that a beautiful purple gas was released. This gas will not form liquid after condensation, but will become dark black crystals with metallic luster. This is iodine.
Today, this reaction can be explained as follows: sulfuric acid meets alkali metal iodide-potassium iodide (KI) and sodium iodide (NaI) contained in seaweed ash to generate hydrogen iodide (HI). It reacts with sulfuric acid to produce free iodine;
H2SO4 + 2HI ——→ 2H2O + SO2↑+ I2 ↑
18 13, courtois published the article "Discovery of New Substances in Algae Ash", and gave the iodine he obtained to French chemists Clemens, De Somerset, Grusack and others at that time for research and identification, which was affirmed by them.
Guy Lussac named it iode, from the Greek word purple. Therefore, the Latin name of iodine and the symbol I of the element are obtained.
[Edit this paragraph] The influence of iodine on people:
Iodine is one of the essential trace elements for human body. The total amount of iodine in healthy adults is 30 mg (20 ~ 50 mg), of which 70%~80% exists in the thyroid gland.
Physiological functions of iodine:
1. Promote biological oxidation: Thyroxine can promote biological oxidation in the tricarboxylic acid cycle, coordinate the coupling of biological oxidation and phosphorylation, and regulate energy conversion.
2. Regulate the synthesis and decomposition of protein: when protein is insufficient, thyroxine can promote the synthesis of protein; When protein is ingested sufficiently, thyroxine can promote the decomposition of protein.
3. Promote the metabolism of sugar and fat: Thyroxine can accelerate the absorption and utilization of sugar, promote the decomposition and oxidation of glycogen and fat, and regulate the concentration of serum cholesterol and phospholipids.
4. Regulation of water and salt metabolism: Thyroxine can promote water and salt in tissues to enter the blood and be discharged from the kidneys. When it is deficient, it can cause water and salt retention in tissues, and interstitial fluid containing a large amount of mucin appears in tissues, resulting in mucinous edema.
5. Promote the absorption and utilization of vitamins: Thyroxine can promote the absorption and utilization of nicotinic acid, the process of transforming carotene into vitamin A and the process of synthesizing riboflavin adenine dinucleotide from riboflavin.
6. Enhance enzyme activity: Thyroxine can activate many enzymes in vivo, such as cytochrome, succinate oxidase, alkaline phosphatase, etc. , and play a role in substance metabolism.
7. Promote growth and development: Thyroxine promotes bone development and protein synthesis, and maintains the normal structure of the central nervous system.
It is worth noting that excessive iodine intake is also harmful, and excessive iodine intake in daily diet can also cause hyperthyroidism. Whether it is necessary to "supplement iodine" in addition to the normal diet, you must go through a formal physical examination and follow the doctor's advice. Never blindly "supplement iodine".
Iodine tincture, compound iodine solution, iodine throat tablets, iodine glycerin and other iodine preparations are widely used in medical treatment. Iodine tincture is a common disinfectant in the family. Iodine poisoning in children is mostly caused by mistake or overdose. Someone once mistook tincture of iodine for cough syrup and gave it to children. A few sick children are allergic to iodine, and the therapeutic dose also has a serious reaction. Children can die if they take 3 ~ 4 ml of iodine tincture by mistake.
Children take high concentration iodine by mistake, which has a strong stimulating and corrosive effect on gastrointestinal tract. After absorption, it reacts with protein in tissues, causing systemic poisoning. After children take it by mistake, there is iodine in the mouth, burning pain in the mouth, esophagus and heartburn, edema and brown in the mouth and throat, which can cause scar and stenosis in the esophagus and stomach after recovery. The sick children also have dizziness, headache, thirst, nausea, vomiting, diarrhea, fever and other symptoms, and blood can be carried in the feces. Children with severe poisoning have pallor, shortness of breath, cyanosis, limb tremor, confusion, disorientation, sensory disorder, speech disorder, even coma and shock, or toxic nephritis, hematuria and proteinuria, which can cause acute renal failure in severe cases. Allergic children can cause anaphylactic shock.
Due to the strong corrosiveness of iodine preparation, it can cause laryngeal edema, even suffocation, and even mental symptoms and coma in severe cases. If it cannot be rescued in time, it will cause severe hypoxia in the brain and damage the central nervous system, thus affecting the child's intellectual development. Therefore, iodine preparations should be kept in a safe place, and children should not be allowed to get them casually. In particular, children should be educated not to eat more iodine throat tablets. In addition, iodine tincture should be placed separately from cough syrup, and the name should be marked to prevent iodine tincture from being mistaken for cough syrup for children to prevent poisoning. If you take a lot of iodine preparations, you should immediately send them to the hospital for emergency treatment, which can alleviate the symptoms.
Children poisoned by oral iodine preparation should be given plenty of starchy food immediately, such as rice soup, lotus root starch, noodles, porridge, bread, biscuits, etc. Then induce vomiting, and then gastric lavage with 1% ~ 10% starch solution or rice soup, or gastric lavage with 1% sodium thiosulfate solution until the washed liquid is blue. Catharsis after gastric lavage, oral rice soup, raw egg white, milk, vegetable oil, etc. To protect the gastric mucosa. Severe laryngeal edema should be given oxygen, and when suffocation occurs, the trachea should be cut immediately and artificial respiration should be carried out. At the same time, we should pay attention to symptomatic treatment.
The national standard requires that the iodine content per 100g milk rice flour is 30- 150μg ... Excessive iodine intake will lead to goiter. The safe upper limit of children's iodine intake announced by the Nutrition Society of China is 800 micrograms per day, but the Institute recommended the daily iodine intake in 2000, which is 50 micrograms for infants, 90 ~ 120 micrograms for children and 150 micrograms for adults.
The latest recommended daily iodine supply of WHO 200 1 is as follows:
0-59 months preschool children 90 micrograms/day.
6- 12 120 μ g/day of school-age children.
/kloc-adults over 0/2 years old150μ g/day
Pregnant and lactating women 200 micrograms/day
Effects of iodine deficiency on different life stages;
Fetus: abortion, stillbirth, congenital malformation, rising birth mortality and neonatal mortality, dementia, mental retardation and fetal hypothyroidism.
Infants: hypothyroidism and goiter in infants.
Children and adolescents: adolescents with hypothyroidism, goiter, mental disorders, developmental retardation and dementia.
Adults: goiter and reproductive system diseases, hypothyroidism, mental disorders.
[Edit this paragraph] How to supplement iodine in daily life
First, eat iodized salt.
The state stipulates that 20 micrograms of iodine should be added to each gram of salt. The whole people can take iodized salt as a simple, safe, effective and economical iodine supplement measure to prevent iodine deficiency disorders.
Iodized salt is a mixture of potassium iodate and salt in a certain proportion. Because iodine is a lively and volatile element, iodized salt can lose 20% ~ 25% during storage and 15% ~ 50% due to improper cooking methods, so it is necessary to use iodized salt correctly.
1, can't be placed in high temperature and sunlight.
2. The storage container should be tightly covered.
3. Take quick cover quickly
4. Add salt when the dish is to be cooked, so as to prevent high-temperature volatilization and reduce the iodine content.
Secondly, kelp, laver, Chinese cabbage, marine fish, shrimp, crab and shellfish are also rich in iodine, so you can eat more.
Third, infants eat iodized milk powder. Considering that the diet of infants is mainly dairy products, the Chinese government also stipulates that iodine must be added to infant milk powder.
[Edit this paragraph] Iodine deficiency
Fetal period 1. Abortion, stillbirth, congenital malformation, perinatal mortality and infant mortality increased;
2. Endemic cretinism
3. Neuromotor function is backward.
4. Fetal hypothyroidism
Neonatal period-neonatal hypothyroidism, neonatal goiter
Childhood and adolescence-goiter, adolescent hypothyroidism, subclinical cretinism, mental retardation, physical retardation, simple deafness.
Adult goiter and its complications, hypothyroidism, mental retardation, hyperthyroidism caused by iodine
Need crowd
Iodine deficiency patients are accompanied by diseases such as thyroid hypertrophy and hypothyroidism.
physiological drives
The recommended intake of iodine for adults is150 ug/d; The maximum tolerable intake is1000 ug/d/d.
Overexpression
Long-term high iodine intake can lead to high iodine harm, such as high iodine goiter.
Brief introduction of iodine
Iodine is an essential trace element for human body (including all animals) and one of halogen elements. Iodine has the weakest chemical activity among halogen elements, but it can still be directly combined with most elements and widely exists in nature in the form of compounds. Iodine is slightly soluble in water and hydrolyzed to form stable hypoiodic acid, which can make brown aqueous solution acidic. Iodine is easily soluble in organic solvents such as ethanol, ether and glycerol. Iodine turns blue when it meets starch, which can be used for qualitative and quantitative detection. Seaweed is the most abundant iodine, which is the main raw material for extracting pure iodine. Industrial iodine also comes from seaweed and is mainly used in medicine, fuel, photosensitive materials and chemical reagents.
The discovery of iodine
In China, as early as the 4th century BC, there was a record of gall disease, namely iodine deficiency. Among them, Jin (4th century A.D.) first treated gall disease with wine extract of seaweed; Sui Fang (7th century AD) put forward the theory that gall disease is related to water and soil. Sun Simiao and Wang Tao in the Tang Dynasty (8th century AD) expanded the use of kelp to treat diseases. It was in the12nd century that seaweed was used to treat goiter abroad, which was about 800 years later than that in China. After centuries of life practice and research on iodine, courtois separated iodine from algae ash for the first time in 18 13. Later named iodine by Grusack; Coindet suggested using iodine preparation to prevent and treat goiter in 1820; 1896, Bowman first confirmed that the thyroid gland has the function of polyiodine, and iodine was separated from the thyroid gland.
food source
The iodine needed by human body mainly comes from food, accounting for about 80%-90% of the total daily intake, followed by drinking water and salt. The iodine content in food depends on the biogeochemical conditions in different regions.
The iodine content of marine life is very high, such as kelp, laver, seafood fish, scallop, mussel, jellyfish, lobster and so on. The iodine content of dried kelp can reach 240 mg/kg; However, the iodine content in soil and air is less in inland mountainous areas far from the ocean or areas that are not easily blown by sea breeze, and the iodine content in food in these areas is not high either.
The iodine content of terrestrial food is higher than that of plant food, slightly higher in eggs and milk, followed by meat, and lower in freshwater fish. Plants have the lowest iodine content, especially fruits and vegetables.
Metabolic absorption
The total daily intake of iodine from food, water and air is about 100-300ug, which is mainly absorbed by the digestive tract in the form of iodide. Some of the organic iodine can be absorbed directly, and the other part can be absorbed only after being converted into inorganic iodine in the digestive tract. The lungs, skin and mucous membranes can also absorb very small amounts of iodine. About 80%-90% of human iodine comes from food, 10%-20% from drinking water and 5% from air.
Iodine in diet and water is mainly inorganic iodide, which is quickly and completely absorbed in the stomach and upper part of small intestine after entering the human body through the mouth. Generally, it is absorbed within 1 hour after entering the gastrointestinal tract, and almost completely absorbed within 3 hours. Organic iodine is absorbed after releasing iodide through intestinal degradation, but about 80% of thyroid hormone iodine can be directly absorbed. Iodine bound to amino acids can be directly absorbed. However, organic iodine-bound fatty acids can enter the blood through the chylous duct without passing through the liver. The absorbed iodine is quickly transported to plasma and distributed in all tissues of the whole body. Dietary calcium, magnesium and some drugs, such as sulfanilamide, have certain obstacles to the absorption of iodine. Protein, when the energy is low. It will also hinder the absorption of iodine in the gastrointestinal tract.
Iodine is mainly used to synthesize thyroid hormone in the body. The thyroid gland has a strong ability to absorb iodine from blood, and the iodine concentration in the thyroid gland is more than 25 times higher than that in plasma.
Iodine absorbed by digestive tract enters portal vein. After the organic iodine is converted into inorganic iodide by the liver, part of it enters the blood circulation and is transported to thyroid, heart, lung, kidney, muscle, skin and other tissues. The other part enters the digestive tract after being filled with bile from the liver, and the other part re-enters the portal vein to reach the liver after being reabsorbed, which is called "intestinal-hepatic circulation". The rest is excreted through the intestine.
physiological function
1. Participate in energy metabolism. In the metabolism of protein, fat and carbohydrate, iodine promotes oxidation and oxidative phosphorylation; Promoting catabolism, energy conversion, increasing oxygen consumption and strengthening heat production are all carried out in the heart, liver, kidney and skeletal muscle, but the effect on the brain is not obvious; Iodine is involved in maintaining and regulating body temperature and maintaining normal metabolism and life activities.
2. Promote the growth and development of metabolism and physique. All mammals must have thyroxine, that is, iodine is needed to maintain their cell differentiation and growth. The height, weight, musculoskeletal growth and sexual development of developing children are bound to involve thyroid hormones. Iodine deficiency will hinder children's growth and development in this period, and one of the most important causes of dwarfism is iodine deficiency. Previous studies have shown that thyroid hormone can promote the synthesis of DNA and protein, the absorption and utilization of vitamins, activate many important enzymes, including cytochrome, succinate oxidase and so on 100, and promote the oxidation and metabolism of organisms.
3. Promote the development of the nervous system. In the stage of brain development, the migration and differentiation of neurons, the differentiation and development of axons, especially the establishment of dendrites, dendritic spines, tactile processes, nerve microtubules and neuronal connections, and the formation and development of myelin sheath all require the participation of thyroid hormones.
4. The role of pituitary hormones The iodine metabolism and the synthesis, release and function of thyroid hormones are regulated by TSH in the anterior pituitary, and the secretion of TSH is influenced by the feedback of plasma thyroid hormone concentration.