Chemical formulas for dummies. Chemical calculations Introduction to nitrogen. Amines
In mineralogy, it is important to be able to calculate the formula of a mineral based on the results of its chemical analysis. This section provides a number of examples of such calculations for different minerals. When the calculations are made and the structural formula is obtained, it becomes clear whether it coincides with the crystal chemical data for the mineral. It should be noted that even if the total sum of components in the analysis turns out to be equal to 100%, this does not always mean that the composition of the mineral is determined correctly and accurately.
5.7.1 Calculation of sulfide analysis
In the case of sulfide minerals, analytical results are usually expressed in mass percentages.
Table 5.1 Results of chemical analysis of iron-containing sphalerite from the Renström deposit, North. Sweden (byR. S. Duckworth and D. Richard,Mineral. Mag. 57:83-91, 1993)
|
Element |
Mac.% |
Atomic |
Atomic |
|
quantities |
ratios |
||
|
at S = 1 |
|||
|
57,93 |
0,886 |
0,858 |
|
|
8,21 |
0,1407 |
0,136 |
|
|
33,09 |
1,032 |
1,000 |
|
|
Sum |
99,23 |
max (wt.%) of elements. Calculating a formula based on data from such analyzes is a simple arithmetic problem. In the example of iron-bearing sphalerite below (Table 5.1), the first step is to divide the mass percentage of each element by its atomic mass to obtain the mole fraction of that element. The structural formula of iron-bearing sphalerite looks like (Zn, Fe)S, and therefore, in order for the results to have the correct relationships, it is necessary to reduce either the sum of the mole fractions of Zn and Fe, or the mole fraction of S, to unity. The formula used, allowing for both completely cationic and completely anionic lattice, is valid for the case under consideration, and if the results of the analysis are correct, then the formulas calculated by both methods should coincide. Thus, bringing S to unity and rounding the resulting values to the second decimal place, we obtain the formula (Zn 086 Fe 014) 100 S. Some sulfide minerals (for example, pyrrhotite Fe 1-x S) have a non-stoichiometric content of cations. In such cases, analyzes should be calculated based on the amount of sulfur ions.
5.7.2 Calculation of silicate analysis
The results of analyzes of rock-forming minerals (see, for example, the analysis of garnet in Table 5.2) are usually expressed in mass percentage of oxides. The calculation of the analysis presented in this form is somewhat more complex and includes a number of additional operations.
molecular weight, which gives the relative content of oxide molecules (column 2).
2. Calculate the atomic quantities of oxygen. To do this, each value in column 2 is multiplied by the number of oxygen atoms in the corresponding oxides, which gives the relative content of oxygen atoms contributed to the formula by each element (column 3).
At the bottom of column 3 is the total number of oxygen atoms (2.7133).
3. If we want to obtain a garnet formula based on 12 oxygen atoms, then it is necessary to recalculate the ratios of oxygen atoms so that their total number is 12. To do this, the numbers in column 3 for each oxide are multiplied by 12/T, where T is the total amount of oxygen from column 3. The results are shown in column 4.
4. Calculate the atomic ratios for various cations. For this purpose, the numbers in column 4 must be multiplied or divided by the values of these ratios, determined by stoichiometry. So, for example, SiO 2 has one silicon per two oxygen. Therefore, the corresponding number in column 4 is divided by 2. In A1 2 0 3, for every three oxygen atoms there are two aluminum atoms, in which case the number in column 4 is multiplied by 2/3. For divalent cations, the numbers in columns 4 and 5 are the same.
Table 5.2 Results of chemical analysis of garnet, Wesselton mine, Kimberley, South Africa (according toA.D. Edgar and N.E. Charbonneau,Am.Mineral. 78: 132-142, 1993)
|
Oxide |
Mmass% oxides |
Molecular quantities oxides |
Atomic amount of oxygen in a molecule |
Number of anions per 12 O atoms, i.e. column (3) x 4.422 |
Number of cations in the formula |
|
Si0 2 |
40,34 |
0,6714 |
1,3426 |
5,937 |
Si 2.968 |
|
A1 2 0 3 |
18,25 |
0,1790 |
0,537 |
2,374 |
Al 1.582 |
|
4,84 |
0,0674 |
0,0674 |
0,298 |
Fe 0.298 |
|
|
0,25 |
0,0035 |
0,0035 |
0,015 |
Mn 0.015 |
|
|
Ti0 2 |
2,10 |
0,0263 |
0,0526 |
0,232 |
Ti 0.116 |
|
Cr 2 0 3 |
2,22 |
0,0146 |
0,0438 |
0,194 |
Cr 0.129 |
|
18,77 |
0,3347 |
0,3347 |
1,480 |
Ca 1.480 |
|
|
13,37 |
0,3317 |
0,3317 |
1,467 |
Mg 1.467 |
|
|
Sum |
100,14 |
2,7133 |
|||
|
12/2,7133 = 4,422 |
The quantities of cations in the formula corresponding to the established number of oxygen atoms (12) and given in column 5 can be grouped in the manner shown in the table in accordance with the structural formula of garnet A 3 B 2 [(Si, Al)0 4 ], where A - divalent cations (Ca, Mg, Fe, Mn), and B - trivalent cations (Al, Cr), as well as Ti 4 +. The deficiency of Si is compensated by Al, which is taken in such quantity as to completely fill the tetrahedral positions. The remaining aluminum atoms are to position B,
To quickly assess the correctness of the arithmetic operations performed, you need to check the balance of valences by summing up the positive and negative charges.
5.7.3 Calculation of analysis in the presence of different anions
In the last example, we will briefly consider the calculation of the formula based on the results of analysis in the presence of different anions in the mineral composition (Table 5.3). In our case, the mineral is represented by fluorine-apatite Ca 5 (PO 4) 3 ^,0,OH), which, in addition to
Table 5.3 Results of chemical analysis of apatite
|
Oxides |
(!) ~ |
(2.) |
Ch 4) Ka number |
|
|
Wt.% |
Molek |
Molek |
||
|
lar |
lar |
tions in |
||
|
if |
quantity |
based on |
||
|
Na2O K2O P2O5 H2O Sum O=FjCl Sum |
55,08 0,32 0,02 0,05 0,03 0,04 0,0! 42,40 1,63 0,20 1,06 100,84 -0,72 100,12 |
quality 0,9822 0,0020 0,0003 0,0012 0,0003 0,0006 0,0001 0,2987 0,0858 0,0056 0,0567 0,0914 3/2, 5409 = |
va oxygen 0,9822 0,0060 0,0003 0,0012 0,0003 0,0006 0,0001 1,4935 0,0858 0,0056 0,0567 0,0914 2,5409 4, 9386 |
13 anions (4.9386) 4,85 0,02 0,01 0,01 2,95 0,42 0,03 0,56 |
oxygen contains F and Cl. The results of the analysis are again expressed in mass percentage of oxides, although in fact some of them are halogens. In such cases, it is necessary to correct the total amount of oxygen by taking into account the number of moles of oxygen equivalent to the halides present.
So, the calculation includes the following steps.
To do this, the number of moles indicated in column 2 must be multiplied by the stoichiometric
anion number. Remember to subtract the oxygen equivalent (in in this case 0.0914 moles) present in the mineral F and Cl (table bets 3).
3. Sum up the number of anions, remembering to subtract 0.0914 moles of oxygen associated with the F and Cl present (2.5409).
4. If we want to obtain an apatite formula based on 13 anions, then we need to recalculate the ratios of the anions so that their total number is 13. To do this, each of them is multiplied by 13/2.5409, those. at 4.9386.
5. Calculate the ratios of atoms of various cations. To do this, you need to multiply the molecular quantities given in column 2 by 4.9386, and then multiply or divide the resulting values by the values of these ratios, determined by the stoichiometry of the oxides. For example, at P 2 O 5 on There are two phosphorus atoms per mole of oxide. The final results are shown in column 4.
Literature for further study
1. Goldstein, J. L., Newbury, D. E., Echhn, P., Joy, D. S., FiOTi, C. and Lifshm, E. Scanning Electron Microscopy and X-ray Microanalysis. New York, Plenum, 1984.
2. Marfunin, A. S. (ed.]. Methods and Instrumentation: Results and Recent Developments, vol. 2 of Advanced Mineralogy Berlin, Springer-Verlag, 1985.
3. Willard, H. H., Merntt, L. L., Dean, J. A. and Settle, F. A. Instrumental Methods of Analysis, 7th edn. Belmont, CA, Wadsworth, 1988.
Editor's Addition
1. Garanin V.K., Kudryavtseva G.P.The use of electron probe instruments for the study of mineral matter. M, Nedra, 1983, 216 p.
2. Laputina I.P. Microprobe in mineralogy. M., on Science, 1991, 139 p.
The physical properties of minerals are determined by the interaction between structure and chemical composition. These properties include those that affect appearance mineral, such as its luster and color. Other properties affect physical characteristics minerals - hardness, piezoelectricity, magnetism. We will first look at the density of minerals, since this property is directly related to their structure and composition.
On their basis, schemes and equations of chemical reactions are drawn up, as well as chemical classification and nomenclature of substances. One of the first to use them was the Russian chemist A. A. Iovsky.
A chemical formula may indicate or reflect:
- 1 molecule (as well as ion, radical...) or 1 mole of a specific substance;
- qualitative composition: what chemical elements the substance consists of;
- quantitative composition: how many atoms of each element does a molecule (ion, radical...) contain?
For example, the formula HNO 3 means:
- 1 molecule of nitric acid or 1 mole of nitric acid;
- qualitative composition: the nitric acid molecule consists of hydrogen, nitrogen and oxygen;
- quantitative composition: a nitric acid molecule contains one hydrogen atom, one nitrogen atom and three oxygen atoms.
Kinds
Currently, the following types of chemical formulas are distinguished:
- The simplest formula . It can be obtained experimentally by determining the ratio of chemical elements in a substance using the atomic mass values of the elements. So, the simplest formula of water is H 2 O, and the simplest formula of benzene is CH (unlike C 6 H 6 - true). Atoms in formulas are indicated by signs chemical elements, and their relative quantity - numbers in subscript format.
- True Formula . Molecular formula - can be obtained if the molecular mass of a substance is known. The true formula of water is H 2 O, which coincides with the simplest one. The true formula of benzene is C 6 H 6, which differs from the simplest one. True formulas are also called gross formulas . They reflect the composition, but not the structure, of the molecules of a substance. The true formula shows the exact number of atoms of each element in one molecule. This quantity corresponds to a [lower] index - a small number after the symbol of the corresponding element. If the index is 1, that is, there is only one atom of a given element in the molecule, then such an index is not indicated.
- Rational formula . Rational formulas highlight groups of atoms characteristic of classes of chemical compounds. For example, for alcohols the group -OH is allocated. When writing a rational formula, such groups of atoms are enclosed in parentheses (OH). The number of repeating groups is indicated by numbers in subscript format, which are placed immediately after the closing bracket. Square brackets are used to reflect the structure of complex compounds. For example, K4 is potassium hexacyanocobaltate. Rational formulas are often found in a semi-expanded form, when some of the same atoms are shown separately to better reflect the structure of the molecule of a substance.
- Markush formula represent a formula in which the active nucleus and a number of substituent options are isolated, combined into a group of alternative structures. It is a convenient way to designate chemical structures in a generalized form. The formula refers to the description of an entire class of substances. The use of “broad” Markush formulas in chemical patents leads to a lot of problems and discussions.
- Empirical formula. Different authors may use this term to mean the simplest , true or rational formulas.
- Structural formula. Graphically shows the relative arrangement of atoms in a molecule. Chemical bonds between atoms are indicated by lines (dashes). There are two-dimensional (2D) and three-dimensional (3D) formulas. Two-dimensional are a reflection of the structure of matter on a plane (also skeletal formula- attempts to approximate a 3D structure on a 2D plane). Three-dimensional [spatial models] allow one to represent its composition most closely to theoretical models of the structure of matter, and, often (but not always), a more complete (true) relative arrangement of atoms, bond angles and distances between atoms.
- The simplest formula: C 2 H 6 O
- True, empirical, or gross formula: C 2 H 6 O
- Rational formula: C 2 H 5 OH
- Rational formula in semi-expanded form: CH 3 CH 2 OH
- Structural formula (3D):
The simplest formula C 2 H 6 O can equally correspond to dimethyl ether (rational formula; structural isomerism): CH 3 -O-CH 3.
There are other ways to write chemical formulas. New methods appeared in the late 1980s with the development of personal computer technology (SMILES, WLN, ROSDAL, SLN, etc.). Personal computers also use special software called molecular editors to work with chemical formulas.
Notes
- Basic concepts of chemistry (undefined) (unavailable link). Retrieved November 23, 2009. Archived November 21, 2009.
- Distinguish empirical And true formulas. Empirical formula expresses the simplest formula substance (chemical compound), which is determined by elemental analysis. Thus, the analysis shows that simplest, or empirical, the formula of some compound corresponds to CH. True Formula shows how many of these simplest CH groups are contained in the molecule. Let's imagine true formula in the form (CH) x, then at x = 2 we have acetylene C 2 H 2, at x = 6 we have benzene C 6 H 6.
- Strictly speaking, you cannot use the terms “ molecular formula" And " molecular mass"salts, since salts do not contain molecules, but only ordered lattices consisting of ions. None of the sodium ions [cations] in the sodium chloride structure “belong” to any particular chloride ion [anion]. It's correct to talk about chemical formula salt & its corresponding formula mass. Because the chemical formula (true) sodium chloride - NaCl, formula mass sodium chloride is defined as the sum of the atomic masses of one sodium atom and one chlorine atom: 1 sodium atom: 22.990 a. eat.
1 chlorine atom: 35.453 a. eat.
-----------
Total: 58,443 a. eat.
It is customary to call this quantity “
10-1. Write the reaction equations for interaction with water of the following
compounds: SOCl2, PCl3, P2S5, Al4C3, LiAlH4, NaHCO3, Na2SiO3.
10-2. The laboratory has five flasks with aqueous solutions of various
substances. The first flask says “barium hydroxide”, the second says “iodide”
potassium", on the third - "sodium carbonate", on the fourth - "hydrochloric acid" and on
the fifth is “copper nitrate”. The labels are mixed up in such a way that none of the
solutions are not signed correctly. When draining the solution from the second flask with
the solution releases gas from the third flask, while the solution remains
transparent. When mixing the solution from the second flask with the contents
In the fourth flask, a white precipitate is formed, the color of the solution does not change.
1. Indicate the correct labels for flasks Nos. 1–5.
2. Write the equations for the reactions mentioned in the condition.
3. What other reactions can be carried out between these substances?
10-3. Three organic substances are isomers. When burned they
form only CO2 and water. Molecular weight of each of these substances
is 60, while the mass fraction of hydrogen in the molecule is 6 times less than
mass fraction of carbon.
1. Determine the composition of substances, suggest their possible structure.
2. Which of the following compounds interact with a) aqueous
sodium hydroxide solution. c) freshly precipitated copper hydroxide?
Write the reaction equations.
10-4. While sorting out painkillers on the shelves, the pharmacist came across
jar with white crystals. The branded label has almost worn off, and you can
it was possible to read only part of the name of the substance: “S-2-(para-iso...)-
about...ova.......” To titrate an aqueous solution of 1.0 grams of these crystals
4.85 ml of 1 M NaOH solution was consumed. Elemental analysis showed
that in addition to carbon and hydrogen, the substance contains 15.5% oxygen by mass.
Try to restore the gross formula using the available data, and then
the structure of this compound. Justify your choice.
10-5. A sample of the mineral enargite weighing 3.95 g was fired in excess
oxygen. During firing, 896 ml (n.s.) of gas A with hydrogen density was obtained
32, as well as 3.55 g of a mixture of two solid products B and C. When processing mixture B
and In a dilute solution of sodium hydroxide, substance B dissolved with
formation of a salt of a tribasic acid. The molecule of this acid contains
45.10% oxygen by mass. The undissolved residue is
substance B weighs 2.40 g, it is soluble in dilute sulfuric acid with
formation of a blue solution.
1. Determine the quantitative composition (formula) of enargite
2. Determine the oxidation states of its constituent elements. TO
What class of compounds does this mineral belong to?
3. Write the equations for the mentioned reactions.
10-6. When 100 g of a solution containing substance A was boiled,
0.448 l carbon monoxide (IV) (n.s.). After gas evolution stops, the solution
carefully evaporated to obtain 5.72 g of substance. When calcined, the mass of this
substance decreased by 3.60 g.
1. What is substance A?
2. Determine the mass fraction of the substance in the solution obtained after
cessation of gas evolution if the volume of the solution does not change during boiling.
Solutions
10-1.
SOCl2 + H2O = SO2 + 2 HCl or SOCl2 + 2 H2O = H2SO3 + 2 HCl
PCl3 + 3 H2O = H3PO3 + 3 HCl
P2S5 + 8 H2O = 2 H3PO4 + 5 H2S
Since the amount of water is not indicated, reactions with the formation of other phosphoric acids,for example, HPO3 are also the right solution. However, write oxide in productsphosphorus - incorrect, since it is very hygroscopic and interacts with watermuch faster than the original sulfide.
Al4C3 + 12 H2O = 4 Al(OH)3 + 3 CH4
LiAlH4 + 4 H2O = + 4 H2
NaHCO3 in water hydrolyzes to form an alkaline medium.
It is better to write hydrolysis in ionic form, but any way of writingwas assessed as correct.
HCO32– + H2O = H2CO3 + OH–
The same is true for sodium silicate Na2SiO3
SiO32– + H2O = HSiO3– + OH–
10-2.
1. Emission of gas (without formation of sediment) means that the solutions have been drained
sodium carbonate and hydrochloric acid: Na2CO3 + 2 HCl = 2 NaCl + CO2 + H2O (flasks No. 2 + No. 3)
The formation of a white precipitate corresponds to Na2CO3 + Ba(OH)2 = BaCO3 + 2 NaOH (No. 2 + No. 4)
The second flask occurs in both cases, therefore it is sodium carbonate
No. 2 - sodium carbonate
No. 3 - hydrochloric acid
No. 4 - barium hydroxide
No. 1 and No. 5 remained - potassium iodide and copper nitrate. Since all the flasksare labeled incorrectly, then No. 1 is copper nitrate, and No. 5 is potassium iodide(it cannot be the other way around, since number 5 is labeled copper nitrate).
Other reactions that can be carried out between these substances:
2 Cu(NO3)2 + 2 Na2CO3 + H2O = (CuOH)2CO3 + CO2 + 4 NaNO3
Cu(NO3)2 + Ba(OH)2 = Cu(OH)2 + Ba(NO3)2
2 Cu(NO3)2 + 4 KI = 2 CuI + I2 + 4 KNO3
Ba(OH)2 + 2 HCl = BaCl2 + 2H2O
10-3.
Judging by the combustion products, the substance contains only C, H and O.
Since the ratio of C to H by mass is 6:1, then the atomic ratio = 1:2.
There cannot be a hydrocarbon with such a ratio and a molecular weight of 60,
the molecule must also contain oxygen. C2H4O2 is suitable.
As isomers we can offer
CH3COOH acetic acid
HCOOCH3 methyl formate
HOCH2–CHO glycolaldehyde
Reactions: a) with an aqueous solution of NaOH
CH3COOH + NaOH ----------------CH3COONa + H2O neutralization, formation of sodium acetate
HCOOCH3 + NaOH ----------------HCOONA + CH3OH alkaline hydrolysis
HOCH2–CHO + NaOH ----------------OCH2–CHO + H2O (partially)
b) with copper hydroxide
CH3COOH + Cu(OH)2 ---------------- (CH3COO)2Cu + 2H2O neutralization, formation of copper acetate
HOCH2–CHO + 2 Cu(OH)2 ---------------- HOCH2–COOH + Cu2O + 2 H2O oxidation
10-4.
It is obvious from the name that the substance is aromatic; it contains para-substituted
benzene ring, most likely an acid.
Calculation by titration. Amount of NaOH used for titration: 0.00485 mol
Let us assume that the acid is monobasic.
Then her molar mass is 1/0.00485 = 206.18.
analysis, you can find out the number of oxygen atoms: 206.2 x 0.155 = 32, two O atoms,
those. There is only a carboxyl group in the molecule, there is no more oxygen.
Taking into account the presence of one COOH group and a benzene ring, it can be determined
that the gross formula of the substance is C13H18O2
Noting that the benzene ring is substituted in the para position,
carboxylic acid (most likely propionic) is replaced at position 2,
Well, to complete the acquaintance with alcohols, I will give the 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 should be stored without access to air. Otherwise it will turn sour. But chemists know the reason - if you add another oxygen atom to an 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 | ||
|---|---|---|---|---|
| Methane 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 | |
| Propanic 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 |
Distinctive feature organic acids is the presence of a carboxyl group (COOH), which gives such substances acidic properties.
Anyone 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 between 3 and 15% acetic acid, with the rest (mostly) water. Consumption of acetic acid in undiluted form poses a danger to life.
Carboxylic acids can have multiple carboxyl groups. In this case they are called: dibasic, tribasic 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, please note that here there are acids that also have a hydroxyl group, characteristic of alcohols. Such substances are called hydroxycarboxylic acids(or hydroxy acids).
At the bottom, under each of the acids, there is a sign 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 in common with politicians, rebels and other citizens with an active position.
Here these are just fragments of molecules. And now we will figure out what makes them special and get acquainted with a new way of writing chemical formulas.
Generalized formulas have already been mentioned several times in the text: alcohols - (R)-OH and carboxylic acids - (R)-COOH. Let me remind you that -OH and -COOH are functional groups. But R is a radical. It’s not for nothing that he is depicted as the letter R.
To be more specific, a monovalent radical is a part of a molecule lacking one hydrogen atom. Well, if you subtract two hydrogen atoms, you get a divalent radical.
Radicals in chemistry received their own names. Some of them even received Latin designations similar to the designations of the elements. And besides, sometimes in formulas radicals can be indicated in abbreviated form, more reminiscent of gross formulas.
All this is demonstrated in the following table.
| Name | Structural formula | Designation | Brief formula | Example of alcohol | ||
|---|---|---|---|---|---|---|
| Methyl | CH3-() | Me | CH3 | (Me)-OH | CH3OH | |
| Ethyl | CH3-CH2-() | Et | C2H5 | (Et)-OH | C2H5OH | |
| I cut through | 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 everything is clear here. I just want to draw your attention to the column where examples of alcohols are given. Some radicals are written in a form that resembles the gross formula, but the functional group is written separately. For example, CH3-CH2-OH turns into C2H5OH.
And for branched chains like isopropyl, structures with brackets are used.
There is also such a phenomenon as free radicals. These are radicals that, for some reason, have separated from functional groups. In this case, one of the rules with which we began studying the formulas is violated: the number of chemical bonds no longer corresponds to the valency of one of the atoms. Well, or we can say that one of the connections becomes open at one end. Free radicals usually live a short time, because 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 the 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 already guessed from the names, all these substances are united under the general name amines. The functional group ()-NH2 is called amino group. Here are some general formulas of 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 a textbook or the Internet.
But I would also like to talk 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 easier than organic chemistry. Of course, inorganic molecules tend to look much simpler because they don't tend to form complex structures like hydrocarbons. But then we have 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 tell you any of this. The topic of my article is chemical formulas. And with them everything is relatively simple.
Most often used in inorganic chemistry rational formulas. And now we’ll 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 element.
It is designated Ca and has a valency of two. Let's see what compounds it forms with the carbon, oxygen and hydrogen we know.
| 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, you can see that the rational formula is something between a structural and a gross formula. But it is not yet 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 pure form is a soft white metal. It does not occur in nature. But it is quite possible to buy it at a chemical store. It is usually stored in special jars without access to air. Because in air it reacts with oxygen. Actually, that’s why it doesn’t 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 and oxygen produce calcium oxide. This substance also does not occur in nature because it reacts with water:
CaO + H2O -> Ca(OH2)
The result is 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 added to an organic substance, an alcohol is obtained, and if it is added to a metal, a hydroxide is obtained.
But calcium hydroxide does not occur in nature due to the presence of carbon dioxide in the air. I think everyone has heard about this gas. It is formed during the respiration 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 slightly soluble calcium carbonate:
Ca(OH)2 + H2CO3 -> CaCO3"|v" + 2H2O
A down arrow means that as a result of the reaction the substance precipitates.
With further contact of calcium carbonate with carbon dioxide in the presence of water, a reversible reaction occurs to form an acidic salt - calcium bicarbonate, which is highly soluble in water
CaCO3 + CO2 + H2O<=>Ca(HCO3)2
This process affects the hardness of the water. When the temperature rises, 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 over 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 so that the functional groups are visible. In our case it 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 give up electrons while others gain them. Electrons are particles with a negative charge. Element with full set electrons has zero charge. If he gave away 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. There is a special entry for this 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 some kind of 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 been added to it.
Negatively charged ions are called anions. Typically these include acidic residues.
Positively charged ions - cations. Most often these are hydrogen and metals.
And here you can probably fully understand the meaning of rational formulas. The cation is written in them first, followed by 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 stick. 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 consists of several atoms.
And such a substance is ammonia. Its aqueous solution is often called ammonia and is included in any first aid kit. Ammonia is a compound of hydrogen and nitrogen and has the rational formula NH3. Let's consider chemical reaction which occurs when ammonia is dissolved in water:
NH3 + H2O<=>NH4^+ + OH^-
The same thing, 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 one hydrogen atom moving from a water molecule to an ammonia molecule. But this atom moved without its electron. The anion is already familiar to us - it is a hydroxide ion. And the cation is called ammonium. It exhibits properties similar to metals. For example, it may combine with an acidic residue. The substance formed by combining 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. Typically equations use rational formulas:
2NH4^+ + CO3^2-<=>(NH4)2CO3
Hill system
So, we can assume that we have already studied structural and rational formulas. But there is another issue that is worth considering in more detail. How do gross formulas differ from rational ones?
We know why the rational formula of carbonic acid is written H2CO3, and not some other way. (The two hydrogen cations come first, followed by the carbonate anion.) But why is the gross formula written CH2O3?
In principle, the rational formula of carbonic acid may well be considered a true formula, because it has no repeating elements. Unlike NH4OH or Ca(OH)2.
But an additional rule is very often applied to gross formulas, which determines the order of elements. The rule is quite simple: carbon is placed first, then hydrogen, and then the remaining 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 a conclusion, I would like to talk about the easyChem system. It is designed so that all the 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 even need some kind of system for deriving formulas? The thing is that the standard way to display information in Internet browsers is hypertext markup language (HTML). It is focused on processing text information.
Rational and gross formulas can be depicted using 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 the following entry in HTML: CH 3-CH 2-OH.
This of course creates some difficulties, but you can live with them. But how to depict the structural formula? In principle, you can use a monospace font:
H H | | H-C-C-O-H | | H H Of course it doesn’t look very nice, but it’s also doable.
The real problem comes when trying to draw benzene rings and when using skeletal formulas. There is no other way left except connecting a raster image. Rasters are stored in separate files. Browsers can include images in gif, png or jpeg format.
To create such files, a graphic 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 cope with this task much better. 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).
The easyChem system allows you to store all formulas directly in an HTML document in text form. In my opinion, this is very convenient.
In addition, the gross formulas in this article are calculated automatically. Because easyChem works in two stages: first the text description is converted into an information structure (graph), and then various actions can be performed on 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, to prepare this article, I only used a text editor. Moreover, I didn’t have to think about which of the formulas would be graphic and which would be text.
Here are a few examples that reveal the secret of preparing the text of an article: Descriptions from the left column are automatically turned 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 numerical coefficients are displayed interlinearly.
In the second line, the expanded formula is given in the form of three separate chains separated by a symbol; I think it is easy to see that the textual description is in many ways reminiscent of the actions that would be required to depict the formula with a pencil on paper.
The third line demonstrates the use of slanted lines using the \ and / symbols. The ` (backtick) sign means the line is drawn from right to left (or bottom to top).
There is much more detail here documentation on using the easyChem system.
Let me finish this article and wish you good luck in studying chemistry.