Chemical formula is an image with symbols .
Signs of chemical elements
chemical sign or element chemical symbol is the first or two first letters of the Latin name of this element.
For example: Ferrum-Fe , cuprum-Cu , oxygenium-O etc.
Table 1: Information provided by the chemical mark
| Intelligence | On the example of Cl |
| Element name | Chlorine |
| Non-metal, halogen | |
| One item | 1 chlorine atom |
| (ar) given element | Ar(Cl) = 35.5 |
| Absolute atomic mass of a chemical element
m = Ar 1.66 10 -24 g = Ar 1.66 10 -27 kg |
M (Cl) \u003d 35.5 1.66 10 -24 \u003d 58.9 10 -24 g |
The name of a chemical sign in most cases is read as the name of a chemical element. For example, K - potassium, Ca - calcium, Mg - magnesium, Mn - manganese.
Cases where the name of the chemical mark is read differently are given in Table 2:
| Name of the chemical element | chemical sign | The name of the chemical symbol
(pronunciation) |
| Nitrogen | N | En |
| Hydrogen | H | Ash |
| Iron | Fe | Ferrum |
| Gold | Au | Aurum |
| Oxygen | O | ABOUT |
| Silicon | Si | Silicium |
| Copper | Cu | Cuprum |
| Tin | sn | Stanum |
| Mercury | hg | hydrargium |
| Lead | Pb | Plumbum |
| Sulfur | S | Es |
| Silver | Ag | Argentum |
| Carbon | C | Tse |
| Phosphorus | P | Pe |
Chemical formulas of simple substances
The chemical formulas of most simple substances (all metals and many non-metals) are the signs of the corresponding chemical elements.
So substance iron And chemical element iron are labeled the same Fe .
If it has a molecular structure (exists in the form , then its formula is the chemical sign of the element with index bottom right, indicating number of atoms in a molecule: H2, O2, O 3, N 2, F2, Cl2, Br2, P4, S8.
Table 3: Information provided by the chemical mark
| Intelligence | For example C |
| Substance name | Carbon (diamond, graphite, graphene, carbine) |
| Belonging of an element to a given class of chemical elements | Non-metal |
| One element atom | 1 carbon atom |
| Relative atomic mass (ar) the element that makes up the substance | Ar(C)=12 |
| Absolute atomic mass | M (C) \u003d 12 1.66 10-24 \u003d 19.93 10 -24 g |
| One substance | 1 mole of carbon, i.e. 6.02 10 23 carbon atoms |
| M(C) = Ar(C) = 12 g/mol |
Chemical formulas of complex substances
The formula of a complex substance is compiled by writing the signs of the chemical elements of which this substance consists, indicating the number of atoms of each element in the molecule. In this case, as a rule, chemical elements are written in order of increasing electronegativity according to the following practice series:
Me , Si , B , Te , H , P , As , I , Se , C , S , Br , Cl , N , O , F
For example, H2O , CaSO4 , Al2O3 , CS2 , OF 2 , NaH.
The exception is:
- some compounds of nitrogen with hydrogen (for example, ammonia NH3 , hydrazine N 2H4 );
- salts of organic acids (for example, sodium formate HCOONa , calcium acetate (CH 3COO) 2Ca) ;
- hydrocarbons ( CH 4 , C 2 H 4 , C 2 H 2 ).
Chemical formulas of substances that exist in the form dimers (NO 2 , P2O 3 , P2O5, monovalent mercury salts, for example: HgCl , HgNO3 etc.), is written in the form N 2 O 4 ,P4 O 6 ,P4 O 10 ,Hg 2 Cl2,Hg 2 ( NO 3) 2 .
The number of atoms of a chemical element in a molecule and a complex ion is determined based on the concept valency or oxidation states and recorded index bottom right from the sign of each element (index 1 is omitted). This is based on the rule:
the algebraic sum of the oxidation states of all atoms in a molecule must be equal to zero (the molecules are electrically neutral), and in a complex ion, the charge of the ion.
For example:
2Al 3 + + 3SO 4 2- \u003d Al 2 (SO 4) 3
The same rule is used when determining the degree of oxidation of a chemical element according to the formula of a substance or complex. Usually it is an element that has several oxidation states. The oxidation states of the remaining elements forming the molecule or ion must be known.
The charge of a complex ion is the algebraic sum of the oxidation states of all the atoms that form the ion. Therefore, when determining the oxidation state of a chemical element in a complex ion, the ion itself is enclosed in brackets, and its charge is taken out of brackets.
When compiling formulas for valence the substance is represented as a compound consisting of two particles of different types, the valences of which are known. Further enjoy rule:
in a molecule, the product of valence and the number of particles of one type must be equal to the product of valence and the number of particles of another type.
For example:
The number in front of a formula in a reaction equation is called coefficient. She indicates either number of molecules, or number of moles of a substance.
The coefficient before the chemical sign, indicates the number of atoms of a given chemical element, and in the case when the sign is a formula of a simple substance, the coefficient indicates either number of atoms, or the number of moles of this substance.
For example:
- 3 Fe- three iron atoms, 3 moles of iron atoms,
- 2 H- two hydrogen atoms, 2 mol hydrogen atoms,
- H2- one molecule of hydrogen, 1 mole of hydrogen.
The chemical formulas of many substances have been determined empirically, which is why they are called "empirical".
Table 4: Information provided by the chemical formula of a complex substance
| Intelligence | For example C aCO3 |
| Substance name | Calcium carbonate |
| Belonging of an element to a certain class of substances | Medium (normal) salt |
| One molecule of a substance | 1 molecule of calcium carbonate |
| One mole of a substance | 6.02 10 23 molecules CaCO3 |
| Relative molecular weight of the substance (Mr) | Mr (CaCO3) \u003d Ar (Ca) + Ar (C) + 3Ar (O) \u003d 100 |
| Molar mass of a substance (M) | M (CaCO3) = 100 g/mol |
| Absolute molecular weight of a substance (m) | M (CaCO3) = Mr (CaCO3) 1.66 10 -24 g = 1.66 10 -22 g |
| Qualitative composition (what chemical elements form a substance) | calcium, carbon, oxygen |
| The quantitative composition of the substance: | |
| The number of atoms of each element in one molecule of a substance: | The calcium carbonate molecule is made up of 1 atom calcium, 1 atom carbon and 3 atoms oxygen. |
| The number of moles of each element in 1 mole of a substance: | In 1 mol CaCO 3(6.02 10 23 molecules) contains 1 mol(6.02 10 23 atoms) calcium, 1 mol(6.02 10 23 atoms) carbon and 3 mol(3 6.02 10 23 atoms) of the chemical element oxygen) |
| Mass composition of the substance: | |
| The mass of each element in 1 mole of a substance: | 1 mole of calcium carbonate (100g) contains chemical elements: 40g calcium, 12g carbon, 48g oxygen. |
| Mass fractions of chemical elements in a substance (composition of a substance in percent by weight):
|
Composition of calcium carbonate by mass:
W (Ca) \u003d (n (Ca) Ar (Ca)) / Mr (CaCO3) \u003d (1 40) / 100 \u003d 0.4 (40%) W (C) \u003d (n (Ca) Ar (Ca)) / Mr (CaCO3) \u003d (1 12) / 100 \u003d 0.12 (12%) W (O) \u003d (n (Ca) Ar (Ca)) / Mr (CaCO3) \u003d (3 16) / 100 \u003d 0.48 (48%) |
| For a substance with an ionic structure (salts, acids, bases) - the formula of a substance gives information about the number of ions of each type in a molecule, their number and mass of ions in 1 mol of a substance:
|
Molecule CaCO 3 is made up of an ion Ca 2+ and ion CO 3 2-
1 mol ( 6.02 10 23 molecules) CaCO 3 contains 1 mol of Ca 2+ ions And 1 mole of ions CO 3 2-; 1 mole (100g) of calcium carbonate contains 40g ions Ca 2+ And 60g ions CO 3 2- |
| Molar volume of a substance under normal conditions (only for gases) | |
Graphic formulas
For more information about a substance use graphic formulas , which indicate the order in which atoms are connected in a molecule And valency of each element.
Graphic formulas of substances consisting of molecules, sometimes, to one degree or another, reflect the structure (structure) of these molecules, in these cases they can be called structural .
To draw up a graphical (structural) formula of a substance, you must:
- Determine the valence of all chemical elements that form a substance.
- Write down the signs of all chemical elements that form a substance, each in an amount equal to the number of atoms of a given element in a molecule.
- Connect the signs of chemical elements with dashes. Each line denotes a pair that makes a connection between chemical elements and therefore equally belongs to both elements.
- The number of dashes surrounding the sign of a chemical element must correspond to the valence of this chemical element.
- When formulating oxygen-containing acids and their salts, hydrogen atoms and metal atoms are bound to the acid-forming element through an oxygen atom.
- Oxygen atoms are connected to each other only when formulating peroxides.
Examples of graphic formulas:
oxides- compounds of elements with oxygen, the oxidation state of oxygen in oxides is always -2.
Basic oxides form typical metals with C.O. +1,+2 (Li 2 O, MgO, CaO, CuO, etc.).
Acid oxides form non-metals with S.O. more than +2 and metals with S.O. from +5 to +7 (SO 2, SeO 2, P 2 O 5, As 2 O 3, CO 2, SiO 2, CrO 3 and Mn 2 O 7). Exception: NO 2 and ClO 2 oxides do not have corresponding acidic hydroxides, but they are considered acidic.
Amphoteric oxides formed by amphoteric metals with S.O. +2,+3,+4 (BeO, Cr 2 O 3 , ZnO, Al 2 O 3 , GeO 2 , SnO 2 and PbO).
Non-salt-forming oxides- oxides of non-metals with С.О. + 1, + 2 (СО, NO, N 2 O, SiO).
Foundations (main hydroxides ) - complex substances that consist of a metal ion (or ammonium ion) and a hydroxo group (-OH).
Acid hydroxides (acids)- complex substances that consist of hydrogen atoms and an acid residue.
Amphoteric hydroxides formed by elements with amphoteric properties.
salt- complex substances formed by metal atoms combined with acidic residues.
Medium (normal) salts- all hydrogen atoms in acid molecules are replaced by metal atoms.
Acid salts- hydrogen atoms in the acid are partially replaced by metal atoms. They are obtained by neutralizing a base with an excess of an acid. To properly name acid salt, it is necessary to add the prefix hydro- or dihydro- to the name of the normal salt, depending on the number of hydrogen atoms that make up the acid salt.
For example, KHCO 3 is potassium bicarbonate, KH 2 PO 4 is potassium dihydroorthophosphate
It must be remembered that acid salts can only form two or more basic acids.
Basic salts- hydroxo groups of the base (OH -) are partially replaced by acidic residues. To name basic salt, it is necessary to add the prefix hydroxo- or dihydroxo- to the name of the normal salt, depending on the number of OH groups that make up the salt.
For example, (CuOH) 2 CO 3 is copper (II) hydroxocarbonate.
It must be remembered that basic salts are capable of forming only bases containing two or more hydroxo groups in their composition.
double salts- in their composition there are two different cations, they are obtained by crystallization from a mixed solution of salts with different cations, but the same anions. For example, KAl (SO 4) 2, KNaSO 4.
mixed salts- in their composition there are two different anions. For example, Ca(OCl)Cl.
Hydrate salts (crystalline hydrates) - they include molecules of crystallization water. Example: Na 2 SO 4 10H 2 O.
Trivial names of commonly used inorganic substances:
| Formula | Trivial name |
| NaCl | halite, rock salt, table salt |
| Na 2 SO 4 * 10H 2 O | Glauber's salt |
| NaNO 3 | Sodium, Chilean nitrate |
| NaOH | caustic soda, caustic, caustic soda |
| Na 2 CO 3 * 10H 2 O | crystal soda |
| Na2CO3 | soda ash |
| NaHCO3 | food (drinking) soda |
| K2CO3 | potash |
| KOH | caustic potash |
| KCl | potassium salt, sylvin |
| KClO 3 | Berthollet salt |
| KNO 3 | Potash, Indian saltpeter |
| K3 | red blood salt |
| K4 | yellow blood salt |
| Kfe 3+ | Prussian blue |
| Kfe 2+ | turnbull blue |
| NH4Cl | ammonium chloride |
| NH 3 *H 2 O | ammonia, ammonia water |
| (NH 4) 2 Fe (SO 4) 2 | mora salt |
| CaO | quicklime (burnt) lime |
| Ca(OH) 2 | slaked lime, lime water, milk of lime, lime dough |
| CaSO 4 * 2H 2 O | Gypsum |
| CaCO3 | marble, limestone, chalk, calcite |
| Sanro 4 × 2H2O | Precipitate |
| Ca (H 2 RO 4) 2 | double superphosphate |
| Ca (H 2 PO 4) 2 + 2CaSO 4 | simple superphosphate |
| CaOCl 2 (Ca(OCl) 2 + CaCl 2) | bleaching powder |
| MgO | magnesia |
| MgSO 4 * 7H 2 O | Epsom salt (bitter) |
| Al2O3 | corundum, bauxite, alumina, ruby, sapphire |
| C | diamond, graphite, soot, coal, coke |
| AgNO3 | lapis |
| (CuOH) 2 CO 3 | malachite |
| Cu 2 S | copper luster, chalcosine |
| CuSO 4 * 5H 2 O | blue vitriol |
| FeSO 4 * 7H 2 O | inkstone |
| FeS 2 | pyrite, iron pyrite, sulfur pyrite |
| FeCO 3 | siderite |
| Fe 2 O 3 | red ironstone, hematite |
| Fe 3 O 4 | magnetic iron ore, magnetite |
| FeO × nH 2 O | brown ironstone, limonite |
| H2SO4 × nSO3 | oleum solution of SO 3 in H 2 SO 4 |
| N2O | laughing gas |
| NO 2 | brown gas, fox tail |
| SO 3 | sulfuric gas, sulfuric anhydride |
| SO2 | sulfur dioxide, sulfur dioxide |
| CO | carbon monoxide |
| CO2 | carbon dioxide, dry ice, carbon dioxide |
| SiO2 | silica, quartz, river sand |
| CO + H2 | water gas, synthesis gas |
| Pb(CH 3 COO) 2 | lead sugar |
| PbS | lead luster, galena |
| ZnS | zinc blende, sphalerite |
| HgCl 2 | corrosive sublimate |
| HgS | cinnabar |
TRIVIAL NAMES OF SUBSTANCES. For many centuries and millennia, people have used a wide variety of substances in their practical activities. Many of them are mentioned in the Bible (these are precious stones, and dyes, and various incense). Of course, each of them was given a name. Of course, it had nothing to do with the composition of matter. Sometimes the name reflected an appearance or a special property, real or imagined. A typical example is a diamond. In Greek damasma - subjugation, taming, damao - I crush; accordingly, adamas - indestructible (it is interesting that in Arabic "al-mas" - the hardest, the hardest). In ancient times, miraculous properties were attributed to this stone, for example, this: if a diamond crystal is placed between a hammer and an anvil, then they will shatter into smithereens rather than the “king of stones” will be damaged. In fact, the diamond is very fragile and does not withstand blows at all. But the word "brilliant" really reflects the property of a cut diamond: in French brilliant - brilliant.
Many names of substances were invented by alchemists. Some of them have survived to this day. Thus, the name of the zinc element (M.V. Lomonosov introduced it into the Russian language) probably comes from the ancient Germanic tinka - “white”; Indeed, the most common zinc preparation, ZnO oxide, is white. At the same time, alchemists came up with many of the most fantastic names - partly because of their philosophical views, partly - to classify the results of their experiments. For example, they called the same zinc oxide “philosophical wool” (alchemists obtained this substance in the form of a loose powder). Other names were based on the methods of obtaining the substance. For example, methyl alcohol was called wood alcohol, and calcium acetate was called “burnt-wood salt” (dry distillation of wood was used to obtain both substances, which, of course, led to its charring - “burning”). Very often the same substance received several names. For example, even by the end of the 18th century. there were four names for copper sulfate, ten for copper carbonate, and twelve for carbon dioxide!
The description of chemical procedures was also ambiguous. So, in the works of M.V. Lomonosov, one can come across a mention of the “loose bastard”, which can confuse the modern reader (although in cookbooks sometimes there are recipes according to which you need to “dissolve a kilogram of sugar in a liter of water”, and “bastard” simply means "sediment").
Currently, the names of substances are regulated by the rules of chemical nomenclature (from the Latin nomenclatura - painting names). In chemistry, nomenclature is a system of rules, using which, each substance can be given a “name” and, conversely, knowing the “name” of a substance, write down its chemical formula. It is not easy to develop a single, unambiguous, simple and convenient nomenclature: suffice it to say that even today there is no complete unity among chemists on this score. The issues of nomenclature are handled by a special commission of the International Union of Pure and Applied Chemistry - IUPAC (according to the initial letters of the English name International Union of Pure and Applied Chemistry). And national commissions develop rules for applying the IUPAC recommendations to the language of their country. So, in Russian, the old term "oxide" was replaced by the international "oxide", which was also reflected in school textbooks.
Anecdotal stories are also associated with the development of a system of national names for chemical compounds. For example, in 1870 the commission on chemical nomenclature of the Russian Physico-Chemical Society discussed the proposal of one chemist to name compounds according to the same principle as names, patronymics and surnames are built in Russian. For example: Potassium Khlorovich (KCl), Potassium Khlorovich Trikislov (KClO 3), Chlor Vodorodovich (HCl), Hydrogen Kislorodovich (H 2 O). After a long debate, the commission decided: to postpone the discussion of this issue until January, without specifying at the same time - what year. Since then, the commission has not returned to this issue.
Modern chemical nomenclature is more than two centuries old. In 1787, the famous French chemist Antoine Laurent Lavoisier presented to the Academy of Sciences in Paris the results of the work of the commission headed by him to create a new chemical nomenclature. In accordance with the proposals of the commission, new names were given to chemical elements, as well as complex substances, taking into account their composition. The names of the elements were chosen so that they reflect the features of their chemical properties. Thus, the element that Priestley previously called “dephlogisticated air”, Scheele called “fiery air”, and Lavoisier himself called “vital air”, received the name oxygen according to the new nomenclature (then it was believed that acids necessarily included this element). Acids are named from their respective elements; as a result, "saltpeter fumed acid" turned into nitric acid, and "vitriol" into sulfuric acid. To designate salts, the names of acids and the corresponding metals (or ammonium) began to be used.
The adoption of the new chemical nomenclature made it possible to systematize vast factual material and greatly facilitated the study of chemistry. Despite all the changes, the basic principles laid down by Lavoisier have survived to this day. Nevertheless, among chemists, and especially among non-professionals, many so-called trivial (from Latin trivialis - ordinary) names have been preserved, which are sometimes used incorrectly. For example, a person who feels bad is offered to “smell ammonia”. For a chemist, this is nonsense, since ammonia (ammonium chloride) is an odorless salt. In this case, ammonia is confused with ammonia, which really has a pungent odor and excites the respiratory center.
A lot of trivial names of chemical compounds are still used by artists, technologists, builders (ochre, mummy, minium, cinnabar, litharge, fluff, etc.). Even more trivial names among medicines. In directories, you can find up to a dozen or more different synonyms for the same drug, which is mainly due to brand names adopted in different countries (for example, domestic piracetam and imported nootropil, Hungarian seduxen and Polish relanium, etc.).
Chemists also often use trivial names for substances, sometimes quite curious ones. For example, 1,2,4,5-tetramethylbenzene has the trivial name "durol", and 1,2,3,5-tetramethylbenzene - "isodurol". A trivial name is much more convenient if it is obvious to everyone what is at stake. For example, even a chemist would never call ordinary sugar "alpha-D-glucopyranosyl-beta-D-fructofuranoside", but would use the trivial name for this substance, sucrose. And even in inorganic chemistry, the systematic, strictly by nomenclature, name of many compounds can be cumbersome and inconvenient, for example: O 2 - dioxygen, O 3 - trioxygen, P 4 O 10 - tetraphosphorus decaoxide, H 3 PO 4 - hydrogen tetraoxophosphate (V) , ВаSO 3 - barium trioxosulfate, Cs 2 Fe (SO 4) 2 - iron (II)-dicesium tetraoxosulfate (VI), etc. And although the systematic name fully reflects the composition of the substance, in practice they use trivial names: ozone, phosphoric acid, etc.
Among chemists, nominal names of many compounds are also common, especially complex salts, such as the Zeise salt K.H 2 O - named after the Danish chemist William Zeise. Such short names are very convenient. For example, instead of "potassium nitrosodisulfonate" a chemist will say "Frémy's salt", instead of "crystal hydrate of double ammonium-iron(II) sulfate" - Mohr's salt, etc.
The table shows the most common trivial (everyday) names of some chemical compounds, with the exception of highly specialized, obsolete, medical terms, and the names of minerals, as well as their traditional chemical names.
| Table 1. TRIVIAL (HOUSEHOLD) NAMES OF SOME CHEMICAL COMPOUNDS | ||
| Trivial name | chemical name | Formula |
| Alabaster | Calcium sulfate hydrate (2/1) | 2CaSO4 . H2O |
| Anhydrite | calcium sulfate | CaSO4 |
| Orpiment | Arsenic sulfide | As 2 S 3 |
| White lead | Basic lead carbonate | 2PbCO3 . Pb(OH)2 |
| White titanium | Titanium(IV) oxide | TiO2 |
| White zinc | zinc oxide | ZnO |
| Prussian blue | Iron(III)-potassium hexacyanoferrate(II) | KFe |
| Bertoletova salt | potassium chlorate | KClO 3 |
| Marsh gas | Methane | CH 4 |
| Bura | Sodium tetraborate tetrahydrate | Na 2 B 4 O 7 . 10H2O |
| Laughing gas | Nitric oxide(I) | N2O |
| Hyposulfite (photo) | Sodium thiosulfate pentahydrate | Na 2 S 2 O 3 . 5H 2 O |
| Glauber's salt | Sodium sulfate decahydrate | Na2SO4 . 10H2O |
| Lead litharge | Lead(II) oxide | PbO |
| Alumina | Aluminium oxide | Al2O3 |
| Epsom salt | Magnesium sulfate heptahydrate | MgSO4 . 7H2O |
| Caustic soda (caustic) | Sodium hydroxide | NaOH |
| caustic potash | Potassium hydroxide | KOH |
| yellow blood salt | Potassium hexacyanoferrate(III) trihydrate | K 4 Fe(CN) 6 . 3H2O |
| yellow cadmium | Cadmium sulfide | CDS |
| Magnesia | magnesium oxide | MgO |
| Lime slaked (fluff) | calcium hydroxide | Ca(OH) 2 |
| Burnt lime (quicklime, boiled) | calcium oxide | Cao |
| Calomel | Mercury(I) chloride | Hg2Cl2 |
| Carborundum | Silicon carbide | SiC |
| Alum | Dodecahydrates of double sulfates of 3- and 1-valent metals or ammonium (for example, potassium alum) | M I M III (SO 4) 2 . 12H 2 O (M I - cations Na, K, Rb, Cs, Tl, NH 4; M III - cations Al, Ga, In, Tl, Ti, V, Cr, Fe, Co, Mn, Rh, Ir) |
| Cinnabar | mercury sulfide | HgS |
| red blood salt | Potassium hexacyanoferrate(II) | K 3 Fe(CN) 6 |
| Silica | silicon oxide | SiO2 |
| Vitriol (battery acid) | Sulfuric acid | H 2 SO4 |
| vitriol | Crystalline hydrates of sulfates of a number of divalent metals | M II SO 4 . 7H 2 O (M II - cations Fe, Co, Ni, Zn, Mn) |
| lapis | Silver nitrate | AgNO3 |
| Urea | Urea | CO(NH2)2 |
| Ammonia | Aqueous ammonia solution | NH3 . x H2O |
| ammonium chloride | ammonium chloride | NH4Cl |
| Oleum | Sulfur(III) oxide solution in sulfuric acid | H2SO4 . x SO 3 |
| Perhydrol | 30% aqueous hydrogen peroxide solution | H 2 O 2 |
| Hydrofluoric acid | Aqueous solution of hydrogen fluoride | HF |
| Table (rock) salt | Sodium chloride | NaCl |
| Potash | Potassium carbonate | K 2 CO 3 |
| Soluble glass | Sodium silicate nonahydrate | Na 2 SiO 3 . 9H2O |
| lead sugar | Lead acetate trihydrate | Pb(CH 3 COO) 2 . 3H2O |
| Segnet's (senet's) salt | Potassium sodium tartrate tetrahydrate | KNaC4H4O6 . 4H2O |
| ammonium nitrate | ammonium nitrate | NH4NO3 |
| Potassium saltpeter (Indian) | potassium nitrate | KNO 3 |
| Norwegian saltpeter | calcium nitrate | Ca(NO 3) 2 |
| Chilean saltpeter | sodium nitrate | NaNO 3 |
| Sulfur liver | Sodium polysulfides | Na 2 S x |
| Sulphur dioxide | Sulfur(IV) oxide | SO2 |
| Sulfuric anhydride | Sulfur(VI) oxide | SO 3 |
| Sulfur color | Fine Sulfur Powder | S |
| silica gel | Dried silicic acid gel | SiO2 . x H2O |
| Hydrocyanic acid | Hydrogen cyanide | HCN |
| soda ash | Sodium carbonate | Na2CO3 |
| Caustic soda (see Caustic soda) | ||
| drinking soda | sodium bicarbonate | NaHCO3 |
| Foil | Tin foil | sn |
| Corrosive sublimate | Mercury(II) chloride | HgCl 2 |
| Double superphosphate | Calcium Dihydrogen Phosphate Hydrate | Ca (H 2 RO 4) 2 . H 2 O |
| Superphosphate simple | The same in a mixture with CaSO 4 | |
| Gold leaf | Tin(IV) sulfide or gold foil | SnS 2 , Au |
| Minium lead | Lead(IV) oxide - lead(II) | Pb 3 O 4 (Pb 2 II Pb IV O 4) |
| Minium iron | Diiron(III)-iron(II) oxide | Fe 3 O 4 (Fe II Fe 2 III) O 4 |
| Dry ice | Solid carbon monoxide(IV) | CO2 |
| Bleaching powder | Mixed chloride-calcium hypochlorite | Ca(OCl)Cl |
| Carbon monoxide | Carbon monoxide(II) | SO |
| Carbon dioxide | Carbon monoxide(IV) | CO 2 |
| Phosgene | Carbonyl dichloride | COCl2 |
| Chrome green | Chromium(III) oxide | Cr2O3 |
| Chrompic (potassium) | Potassium dichromate | K2Cr2O7 |
| verdigris | Basic copper acetate | Cu(OH)2 . x Cu(CH 3 COO) 2 |
Ilya Leenson
Well, to complete the acquaintance with alcohols, I will give another formula of another well-known substance - cholesterol. Not everyone knows that it is a monohydric alcohol!
|`/`\\`|<`|w>`\`/|<`/w$color(red)HO$color()>\/`|0/`|/\<`|w>|_q_q_q<-dH>:a_q|0<|dH>`/<`|wH>`\|dH; #a_(A-72)<_(A-120,d+)>-/-/<->`\
I marked the hydroxyl group in it in red.
carboxylic acids
Any winemaker knows that wine must be kept out of the air. Otherwise it will sour. But chemists know the reason - if you add one more oxygen atom to alcohol, you get an acid.Let's look at the formulas of acids that are obtained from alcohols already familiar to us:
| Substance | Skeletal formula | Gross formula | ||
|---|---|---|---|---|
| Methanoic acid (formic acid) |
H/C`|O|\OH | HCOOH | O//\OH | |
| Ethanoic acid (acetic acid) |
H-C-C\O-H; H|#C|H | CH3-COOH | /`|O|\OH | |
| propanoic acid (methylacetic acid) |
H-C-C-C\O-H; H|#2|H; H|#3|H | CH3-CH2-COOH | \/`|O|\OH | |
| Butanoic acid (butyric acid) |
H-C-C-C-C\O-H; H|#2|H; H|#3|H; H|#4|H | CH3-CH2-CH2-COOH | /\/`|O|\OH | |
| Generalized formula | (R)-C\O-H | (R)-COOH or (R)-CO2H | (R)/`|O|\OH |
A distinctive feature of organic acids is the presence of a carboxyl group (COOH), which gives such substances acidic properties.
Everyone who has tried vinegar knows that it is very sour. The reason for this is the presence of acetic acid in it. Typically, table vinegar contains 3 to 15% acetic acid, with the rest (mostly) water. Eating undiluted acetic acid is life-threatening.
Carboxylic acids can have multiple carboxyl groups. In this case they are called: dibasic, tripartite etc...
Food products contain many other organic acids. Here are just a few of them:
The name of these acids corresponds to those food products in which they are contained. By the way, note that there are acids here that also have a hydroxyl group characteristic of alcohols. Such substances are called hydroxycarboxylic acids(or hydroxy acids).
Below each of the acids is signed, specifying the name of the group of organic substances to which it belongs.
Radicals
Radicals are another concept that has influenced chemical formulas. The word itself is probably known to everyone, but in chemistry, radicals have nothing to do with politicians, rebels and other citizens with an active position.
Here they are just fragments of molecules. And now we will figure out what is their peculiarity and get acquainted with a new way of writing chemical formulas.
Above in the text, generalized formulas have already been mentioned several times: alcohols - (R) -OH and carboxylic acids - (R) -COOH. Let me remind you that -OH and -COOH are functional groups. But R is the radical. No wonder it is depicted in the form of the letter R.
More specifically, a univalent radical is a part of a molecule devoid of one hydrogen atom. Well, if you take away two hydrogen atoms, you get a divalent radical.
Radicals in chemistry have their own names. Some of them even received Latin designations, similar to the designations of the elements. And besides, sometimes radicals in formulas can be indicated in an abbreviated form, more reminiscent of gross formulas.
All this is shown in the following table.
| Name | Structural formula | Designation | Short Formula | alcohol example | ||
|---|---|---|---|---|---|---|
| Methyl | CH3-() | Me | CH3 | (Me)-OH | CH3OH | |
| Ethyl | CH3-CH2-() | Et | C2H5 | (Et)-OH | C2H5OH | |
| Propil | CH3-CH2-CH2-() | Pr | C3H7 | (Pr)-OH | C3H7OH | |
| Isopropyl | H3C\CH(*`/H3C*)-() | i-Pr | C3H7 | (i-Pr)-OH | (CH3)2CHOH | |
| Phenyl | `/`=`\//-\\-{} | Ph | C6H5 | (Ph)-OH | C6H5OH | |
I think that everything is clear here. I just want to draw your attention to the column that gives examples of alcohols. Some radicals are written in a form that resembles an empirical formula, but the functional group is written separately. For example, CH3-CH2-OH is converted to C2H5OH.
And for branched chains like isopropyl, constructions with brackets are used.
There is another phenomenon free radicals. These are radicals that for some reason separated from functional groups. In this case, one of the rules with which we began the study of formulas is violated: the number of chemical bonds no longer corresponds to the valency of one of the atoms. Well, or you can say that one of the links becomes open from one end. Usually, free radicals live for a short time, because the molecules tend to return to a stable state.
Introduction to nitrogen. Amines
I propose to get acquainted with another element that is part of many organic compounds. This nitrogen.
It is denoted by the Latin letter N and has a valency of three.
Let's see what substances are obtained if nitrogen is added to familiar hydrocarbons:
| Substance | Expanded structural formula | Simplified structural formula | Skeletal formula | Gross formula |
|---|---|---|---|---|
| Aminomethane (methylamine) |
H-C-N\H;H|#C|H | CH3-NH2 | \NH2 | |
| Aminoethane (ethylamine) |
H-C-C-N\H;H|#C|H;H|#3|H | CH3-CH2-NH2 | /\NH2 | |
| Dimethylamine | H-C-N<`|H>-C-H; H|#-3|H; H|#2|H | $L(1.3)H/N<_(A80,w+)CH3>\dCH3 | /N<_(y-.5)H>\ | |
| Aminobenzene (Aniline) |
H\N|C\\C|C<\H>`//C<|H>`\C<`/H>`||C<`\H>/ | NH2|C\\CH|CH`//C<_(y.5)H>`\HC`||HC/ | NH2|\|`/`\`|/_o | |
| Triethylamine | $slope(45)H-C-C/N\C-C-H;H|#2|H; H|#3|H; H|#5|H;H|#6|H; #N`|C<`-H><-H>`|C<`-H><-H>`|H | CH3-CH2-N<`|CH2-CH3>-CH2-CH3 | \/N<`|/>\| |
As you probably guessed from the names, all these substances are combined under the common name amines. The functional group ()-NH2 is called amino group. Here are some general formulas for amines:
In general, there are no special innovations here. If these formulas are clear to you, then you can safely engage in further study of organic chemistry using some textbook or the Internet.
But I would like to talk more about formulas in inorganic chemistry. You will see how easy it will be to understand them after studying the structure of organic molecules.
Rational formulas
It should not be concluded that inorganic chemistry is simpler than organic. Of course, inorganic molecules tend to look much simpler because they don't tend to form the complex structures that hydrocarbons do. But on the other hand, one has to study more than a hundred elements that make up the periodic table. And these elements tend to combine according to their chemical properties, but with numerous exceptions.
So, I won't say any of this. The topic of my article is chemical formulas. And with them, everything is relatively simple.
The most commonly used in inorganic chemistry are rational formulas. And now we will figure out how they differ from those already familiar to us.
First, let's get acquainted with another element - calcium. This is also a very common item.
It is designated Ca and has a valency of two. Let's see what compounds it forms with carbon, oxygen and hydrogen known to us.
| Substance | Structural formula | rational formula | Gross formula |
|---|---|---|---|
| calcium oxide | Ca=O | CaO | |
| calcium hydroxide | H-O-Ca-O-H | Ca(OH)2 | |
| Calcium carbonate | $slope(45)Ca`/O\C|O`|/O`\#1 | CaCO3 | |
| Calcium bicarbonate | HO/`|O|\O/Ca\O/`|O|\OH | Ca(HCO3)2 | |
| Carbonic acid | H|O\C|O`|/O`|H | H2CO3 |
At first glance, one can see that the rational formula is something in between the structural and gross formulas. But so far it is not very clear how they are obtained. To understand the meaning of these formulas, you need to consider the chemical reactions in which substances participate.
Calcium in its purest form is a soft white metal. It does not occur in nature. But it is quite possible to buy it in a chemical store. It is usually stored in special jars without air access. Because it reacts with oxygen in air. In fact, that is why it does not occur in nature.
So, the reaction of calcium with oxygen:
2Ca + O2 -> 2CaO
The number 2 before the formula of a substance means that 2 molecules are involved in the reaction.
Calcium oxide is formed from calcium and oxygen. This substance also does not occur in nature because it reacts with water:
CaO + H2O -> Ca(OH2)
It turns out calcium hydroxide. If you look closely at its structural formula (in the previous table), you can see that it is formed by one calcium atom and two hydroxyl groups, with which we are already familiar.
These are the laws of chemistry: if a hydroxyl group is attached to an organic substance, alcohol is obtained, and if to a metal, then hydroxide.
But calcium hydroxide is not found in nature due to the presence of carbon dioxide in the air. I think that everyone has heard about this gas. It is formed during the breathing of people and animals, the combustion of coal and petroleum products, during fires and volcanic eruptions. Therefore, it is always present in the air. But it also dissolves quite well in water, forming carbonic acid:
CO2 + H2O<=>H2CO3
Sign<=>indicates that the reaction can proceed in both directions under the same conditions.
Thus, calcium hydroxide dissolved in water reacts with carbonic acid and turns into poorly soluble calcium carbonate:
Ca(OH)2 + H2CO3 -> CaCO3"|v" + 2H2O
The down arrow means that the substance precipitates as a result of the reaction.
Upon further contact of calcium carbonate with carbon dioxide in the presence of water, a reversible reaction occurs to form an acid salt - calcium bicarbonate, which is highly soluble in water.
CaCO3 + CO2 + H2O<=>Ca(HCO3)2
This process affects the hardness of the water. As the temperature rises, the bicarbonate turns back into carbonate. Therefore, in regions with hard water, scale forms in kettles.
Chalk, limestone, marble, tuff and many other minerals are largely composed of calcium carbonate. It is also found in corals, mollusk shells, animal bones, etc...
But if calcium carbonate is heated on a very high heat, it will turn into calcium oxide and carbon dioxide.
This short story about the calcium cycle in nature should explain why rational formulas are needed. So, rational formulas are written in such a way that functional groups are visible. In our case, this is:
In addition, individual elements - Ca, H, O (in oxides) - are also independent groups.ions
I think it's time to get acquainted with ions. This word is probably familiar to everyone. And after studying the functional groups, it doesn’t cost us anything to figure out what these ions are.
In general, the nature of chemical bonds is usually that some elements donate electrons while others receive them. Electrons are particles with a negative charge. An element with a full set of electrons has zero charge. If he gave an electron, then its charge becomes positive, and if he accepted it, then it becomes negative. For example, hydrogen has only one electron, which it gives up quite easily, turning into a positive ion. For this, there is a special record in chemical formulas:
H2O<=>H^+ + OH^-
Here we see that as a result electrolytic dissociation water breaks down into a positively charged hydrogen ion and a negatively charged OH group. The OH^- ion is called hydroxide ion. It should not be confused with the hydroxyl group, which is not an ion, but part of a molecule. The + or - sign in the upper right corner shows the charge of the ion.
But carbonic acid never exists as an independent substance. In fact, it is a mixture of hydrogen ions and carbonate ions (or bicarbonate ions):
H2CO3 = H^+ + HCO3^-<=>2H^+ + CO3^2-
The carbonate ion has a charge of 2-. This means that two electrons have joined it.
Negatively charged ions are called anions. Usually these include acidic residues.
Positively charged ions cations. Most often it is hydrogen and metals.
And here you can probably fully understand the meaning of rational formulas. The cation is written in them first, and then the anion. Even if the formula does not contain any charges.
You probably already guess that ions can be described not only by rational formulas. Here is the skeletal formula of the bicarbonate anion:
Here, the charge is indicated directly next to the oxygen atom, which received an extra electron, and therefore lost one line. Simply put, each extra electron reduces the number of chemical bonds depicted in the structural formula. On the other hand, if some node of the structural formula has a + sign, then it has an additional wand. As always, this fact needs to be demonstrated with an example. But among the substances familiar to us, there is not a single cation that would consist of several atoms.
And such a substance is ammonia. Its aqueous solution is often called ammonia and is part of any first aid kit. Ammonia is a compound of hydrogen and nitrogen and has the rational formula NH3. Consider the chemical reaction that occurs when ammonia is dissolved in water:
NH3 + H2O<=>NH4^+ + OH^-
The same, but using structural formulas:
H|N<`/H>\H + H-O-H<=>H|N^+<_(A75,w+)H><_(A15,d+)H>`/H + O`^-# -H
On the right side we see two ions. They were formed as a result of the fact that one hydrogen atom moved from a water molecule to an ammonia molecule. But this atom moved without its electron. The anion is already familiar to us - it is the hydroxide ion. And the cation is called ammonium. It exhibits properties similar to metals. For example, it can combine with an acid residue. The substance formed by the combination of ammonium with a carbonate anion is called ammonium carbonate: (NH4)2CO3.
Here is the reaction equation for the interaction of ammonium with a carbonate anion, written in the form of structural formulas:
2H|N^+<`/H><_(A75,w+)H>_(A15,d+)H + O^-\C|O`|/O^-<=>H|N^+<`/H><_(A75,w+)H>_(A15,d+)H`|0O^-\C|O`|/O^-|0H_(A-15,d-)N^+<_(A105,w+)H><\H>`|H
But in this form, the reaction equation is given for demonstration purposes. Usually equations use rational formulas:
2NH4^+ + CO3^2-<=>(NH4)2CO3
Hill system
So, we can assume that we have already studied the structural and rational formulas. But there is another issue worth considering in more detail. What is the difference between gross formulas and rational ones?
We know why the rational formula for carbonic acid is written H2CO3 and not otherwise. (Two hydrogen cations come first, followed by the carbonate anion.) But why is the gross formula written as CH2O3?
In principle, the rational formula of carbonic acid may well be considered a true formula, because there are no repeating elements in it. Unlike NH4OH or Ca(OH)2 .
But an additional rule is often applied to gross formulas, which determines the order of the elements. The rule is pretty simple: put carbon first, then hydrogen, and then the rest of the elements in alphabetical order.
So CH2O3 comes out - carbon, hydrogen, oxygen. This is called the Hill system. It is used in almost all chemical reference books. And in this article too.
A little about the easyChem system
Instead of concluding, I would like to talk about the easyChem system. It is designed so that all those formulas that we discussed here can be easily inserted into the text. Actually, all the formulas in this article are drawn using easyChem.
Why do we need any system for the derivation of formulas? The thing is that the standard way to display information in Internet browsers is Hypertext Markup Language (HTML). It is focused on text processing.
Rational and gross formulas can be depicted with the help of text. Even some simplified structural formulas can also be written in text, for example alcohol CH3-CH2-OH. Although for this you would have to use this notation in HTML: CH 3-CH 2-OH.
This of course creates some difficulties, but you can put up with them. But how to represent the structural formula? In principle, one can use a monospaced font:
H H | | H-C-C-O-H | | H H It certainly doesn't look very nice, but it's also feasible.
The real problem arises when trying to represent benzene rings and when using skeletal formulas. There is no other way but to connect the bitmap. Rasters are stored in separate files. Browsers can include gif, png or jpeg images.
To create such files, a graphical editor is required. For example, Photoshop. But I have been familiar with Photoshop for more than 10 years and I can say for sure that it is very poorly suited for depicting chemical formulas.
Molecular editors are much better at this task. But with a large number of formulas, each of which is stored in a separate file, it is quite easy to get confused in them.
For example, the number of formulas in this article is . They are displayed in the form of graphic images (the rest using HTML tools).
easyChem allows you to store all formulas directly in an HTML document in text form. I think it's very convenient.
In addition, the gross formulas in this article are calculated automatically. Because easyChem works in two stages: first, the textual description is converted into an information structure (graph), and then various actions can be performed with this structure. Among them, the following functions can be noted: calculation of molecular weight, conversion to a gross formula, checking for the possibility of output as text, graphic and text rendering.
Thus, for the preparation of this article, I used only a text editor. Moreover, I did not have to think which of the formulas would be graphical and which would be textual.
Here are some examples that reveal the secret of article text preparation: Descriptions from the left column are automatically converted into formulas in the second column.
In the first line, the description of the rational formula is very similar to the displayed result. The only difference is that the numeric coefficients are output as interlinear.
In the second line, the expanded formula is given as three separate strings, separated by a symbol; I think it's easy to see that a text description is a lot like what would be required to draw a formula with a pencil on paper.
The third line demonstrates the use of slanted lines using the characters \ and /. The ` (backtick) sign means that the line is drawn from right to left (or from bottom to top).
There is much more detail here. documentation on using the easyChem system.
On this, let me finish the article and wish you good luck in studying chemistry.
