smallest electrically neutral, chemically indivisible particle
Alternative descriptionsSmall, yes daring (energy)
smallest particle of matter
The smallest particle of a chemical element
On the planet Neptune, for one ... helium, there are 20 similar offspring of hydrogen
Something small, in the "sharing" of which humanity has amassed big troubles
When an electron is lost or gained, it becomes an ion.
The most energetic particle
Molecule constituent
Host of protons and neutrons
What is an isobar
electron acceptor
Nucleon+electron
Divided "indivisible"
. "peaceful" culprit of the Chernobyl disaster
Name of Canadian film director Egoyan
A grain of the universe
Igor Gostev's film "Marked..."
It was this concept that was introduced by the ancient Greek scientist Leucippus to denote the smallest units of being.
The letter "A" in the nuclear power plant
What is an isotope?
What does the world consist of according to the ancient Greek scientist Democritus?
Although it is "indivisible", it can be divided into a nucleus and an electron shell
Invisible piece of matter
Small, yes daring (energetic)
The smallest electrically neutral particle
. "peaceful" Chernobyl
molecular brick
Culprit of the Chernobyl disaster
Even he is splintered
Peaceful, "indivisible"
Molecule component
. "indivisible"
part of a molecule
particle of matter
. "brick of the universe"
microparticle
. "peaceful" particle
Baby with electrons
Particle of matter
smallest particle
. "indivisible" microparticle
It is smaller than a molecule
isotope as it is
Nucleus + electrons
Peaceful until split
energetic particle
Acceptor
Particle of matter
. "and now our peaceful..."
Molecule constituent
The basis of the world according to Democritus
. "grain" of a molecule
What has protons inside?
Gostev's film "Marked ..."
. "detail" for which nuclear power plants are being built
It is split into nuclear power plants
You just can't see him
Greek "indivisible"
Detail for the "assembly" of the molecule
. "indivisible" part of a molecule
The smallest particle of a chemical element
. "brick" of the molecule
The film "Tagged ..."
Ions revolve around it
Nuclear power source
Divisible "indivisibility" of a molecule
fissile particle
. "peaceful", killing all living things
. the "building block" of the molecule
It is split by the nuclear
. "baby" for which nuclear power plants are being built
Base "A" in nuclear power plants
Split by nuclear
That which splits the nuclear
The simplest case of the formula
Nuclear source of big problems
Bohr created his model
Point with non-zero measure
Robot from the movie "Real Steel"
Peaceful before splitting
Particle of an element (chemical)
The smallest particle of a chemical element, consisting of a nucleus and electrons
Atomic Energy
. "Detail" of the molecule
. "Detalka" for the sake of which nuclear power plants are being built
. "Small, but daring" (energetic)
. "Kid" for which they build nuclear power plants
. "Peaceful", killing all living things
. "Indivisible" part of a molecule
. "Indivisible"
. Molecule "grain of sand"
. "Building brick" of the molecule
. "and now our peaceful..."
. "brick of the universe"
. "brick" of the molecule
. "peaceful" culprit of the Chernobyl disaster
. "peaceful" Chernobyl
. "Peaceful" particle
. "Indivisible" microparticle
Anagram for "Tom"
The letter "A" in the nuclear power plant
What has protons inside
Greek "indivisible"
Divisible "indivisibility" of a molecule
Detail for the "assembly" of the molecule
What the world consists of according to the ancient Greek scientist Democritus
M. Greek. indivisible; matter in the extreme limits of its divisibility, an invisible speck of dust, from which all bodies are allegedly composed, every substance, as if from grains of sand. An immeasurable, infinitely small speck of dust, an insignificant amount. chemists, the word atom takes on the meaning of a measure of the affinity of bodies: one oxygen atom absorbs one, two, three iron atoms, which means: these substances are combined in such a multiple ratio. Atomism m. atomistic, atomic doctrine, in physics, taking as a basis that every substance consists of indivisible atoms; atomistics science, knowledge is; atomist m. scientist who holds this belief. He is opposed to the speaker, a dynamic school that rejects the limit of the divisibility of matter and recognizes it as an expression, a manifestation of forces in our world.
A mess of the word "Toma"
Peaceful, "indivisible"
Something small, in the "sharing" of which humanity has made big trouble for itself
Base "A" in nuclear power plants
Divided "indivisible"
Robot from the movie Real Steel
Film "Tagged..."
Gostev's film "Marked..."
Igor Gostev's film "Marked..."
Although it is "indivisible", it can be divided into a nucleus and an electron shell
What is an isotope
Nucleus + electrons
An atom is the smallest integral particle of matter. At its center is the nucleus, around which, like planets around the Sun, electrons revolve. Oddly enough, but this smallest particle was discovered and the concept of it was formulated
ancient Greek and ancient Indian scientists who have neither the proper equipment nor the theoretical base. Their calculations for many centuries existed on the basis of hypotheses, and only in the 17th century, chemists were able to experimentally prove the validity of ancient theories. But science is rapidly moving forward, and at the beginning of the last century, physicists discovered the subatomic components and structures of particles. It was then that such a thing as "indivisible" was refuted. Nevertheless, the concept has already entered into scientific use and has been preserved.
Ancient scientists believed that an atom is an ultra-small pieces of any matter. Physical parameters depend on their shape, massiveness, color and other parameters. For example, Democritus believed that the atoms of fire are extremely sharp, because it burns, particles of solids have rough surfaces that are tightly attached to each other, water atoms are smooth and slippery, because they give fluid fluidity.
Democritus even considered the soul of a person to consist of temporarily connected atoms, which disintegrate when the individual dies.
A more modern structure was proposed at the beginning of the 20th century by the Japanese physicist Nagaoka. He presented a theoretical development, which is that the atom is a planetary system on a microscopic scale, and its structure is similar to that of Saturn. This structure turned out to be wrong. The Bohr-Rutherford model of the atom turned out to be closer to reality, but it also failed to explain all the physical and electrical properties of corpuscles. Only the assumption that the atom is a structure that includes not only corpuscular properties, but also quantum ones, could explain the largest number of observed realities.
Corpuscles can be in a bound state, or they can be in a free state. For example, an oxygen atom combines with another similar particle to make up a molecule. After an electrical discharge, such as a thunderstorm, it combines into
more complex structure - azine, which consists of triatomic molecules. Accordingly, for a certain kind of compounds of atoms, certain physico-chemical conditions are necessary. But there are also stronger bonds between the particles of the molecule. For example, a nitrogen atom is connected to another triple bond, as a result of which the molecule is extremely strong and almost does not change.
If the number of protons in the nucleus) are similarly orbiting, then the atom is electrically neutral. If there is no identity, then the particle has a negative or positive discharge and is called an ion. As a rule, these charged particles are formed from atoms under the influence of electric fields, radiation of various nature, or high temperature. Ions are chemically hyperactive. These charged atoms are capable of reacting dynamically with other particles.
1. Basic concepts, definitions and laws of chemistry
1.2. Atom. Chemical element. simple substance
Atom is a central concept in chemistry. All substances are made up of atoms. Atom - the limit of crushing a substance by chemical methods, i.e. atom - the smallest chemically indivisible particle of matter. The fission of an atom is possible only in physical processes - nuclear reactions and radioactive transformations.
The modern definition of an atom: an atom is the smallest chemically indivisible electrically neutral particle, consisting of a positively charged nucleus and negatively charged electrons.
In nature, atoms exist both in a free (individual, isolated) form (for example, noble gases consist of individual atoms), and as part of various simple and complex substances. It is clear that in the composition of complex substances, atoms are not electrically neutral, but have an excess positive or negative charge (for example, Na + Cl − , Ca 2+ O 2−), i.e. in complex substances, atoms can be in the form of monatomic ions. Atoms and the monatomic ions formed from them are called atomic particles.
The total number of atoms in nature cannot be counted, but they can be classified into narrower types, just as, for example, all trees in a forest are divided into birch, oak, spruce, pine, etc. according to their characteristic features. The nuclear charge is taken as the basis for the classification of atoms according to certain types, i.e. the number of protons in the nucleus of an atom, since it is this characteristic that is preserved, regardless of whether the atom is in a free or chemically bound form.
Chemical element A type of atomic particle with the same nuclear charge.
For example, the chemical element sodium is meant, regardless of whether free sodium atoms or Na + ions in the composition of salts are considered.
Do not confuse the concepts of atom, chemical element and simple substance. An atom is a concrete concept, atoms exist in reality, and a chemical element is an abstract, collective concept. For example, in nature there are specific copper atoms with rounded relative atomic masses of 63 and 65. But the chemical element copper is characterized by an average relative atomic mass given in the periodic table of chemical elements by D.I. Mendeleev, which, taking into account the content of isotopes, is 63.54 (copper atoms with such a value of Ar are absent in nature). An atom in chemistry is traditionally understood as an electrically neutral particle, while a chemical element in nature can be represented by both electrically neutral and charged particles - monatomic ions: , , , .
A simple substance is one of the forms of the existence of a chemical element in nature (another form is a chemical element in the composition of complex substances). For example, the chemical element oxygen in nature exists in the form of a simple substance O 2 and as part of a number of complex substances (H 2 O, Na 2 SO 4 ⋅ 10H 2 O, Fe 3 O 4). Often the same chemical element forms several simple substances. In this case, they speak of allotropy - the phenomenon of the existence of an element in nature in the form of several simple substances. The simple substances themselves are called allotropic modifications ( modifications) . A number of allotropic modifications are known for carbon (diamond, graphite, carbine, fullerene, graphene, tubulenes), phosphorus (white, red and black phosphorus), oxygen (oxygen and ozone). Due to the phenomenon of allotropy, about 5 times more simple substances are known than chemical elements.
Causes of allotropy:
- differences in the quantitative composition of molecules (O 2 and O 3);
- differences in the structure of the crystal lattice (diamond and graphite).
Allotropic modifications of a given element always differ in physical properties and chemical activity. For example, ozone is more active than oxygen, and the melting point of diamond is higher than that of fullerene. Allotropic modifications under certain conditions (changes in pressure, temperature) can transform into each other.
In most cases, the names of a chemical element and a simple substance coincide (copper, oxygen, iron, nitrogen, etc.), so it is necessary to distinguish between the properties (characteristics) of a simple substance as a collection of particles and the properties of a chemical element as a type of atoms with the same nuclear charge.
A simple substance is characterized by a structure (molecular or non-molecular), density, a certain state of aggregation under given conditions, color and smell, electrical and thermal conductivity, solubility, hardness, boiling and melting points (t bale and t pl), viscosity, optical and magnetic properties , molar (relative molecular) weight, chemical formula, chemical properties, methods of preparation and application. It can be said that the properties of a substance are the properties of a set of chemically bound particles, i.e. physical body, since one atom or molecule has no taste, smell, solubility, melting and boiling points, color, electrical and thermal conductivity.
Properties (characteristics) chemical element: atomic number, chemical sign, relative atomic mass, atomic mass, isotopic composition, abundance in nature, position in the periodic system, atomic structure, ionization energy, electron affinity, electronegativity, oxidation states, valence, allotropy phenomenon, mass and mole fraction in the composition of a complex substance, absorption and emission spectra. We can say that the properties of a chemical element are the properties of a single particle or isolated particles.
The differences between the concepts of "chemical element" and "simple substance" are shown in Table. 1.2 using nitrogen as an example.
Table 1.2
Differences between the concepts of "chemical element" and "simple substance" for nitrogen
| Nitrogen - chemical element | Nitrogen is a simple substance |
|---|---|
| 1. Atomic number 7. | 1. Gas (n.o.s.) colorless, odorless and tasteless, non-toxic. |
| 2. Chemical sign N. | 2. Nitrogen has a molecular structure, the formula is N 2, the molecule consists of two atoms. |
| 3. Relative atomic mass 14. | 3. Molar mass 28 g/mol. |
| 4. In nature, it is represented by nuclides 14 N and 15 N. | 4. Poorly soluble in water. |
| 5. Mass fraction in the earth's crust 0.030% (16th place in prevalence). | 5. Density (N.O.) 1.25 g / dm 3, slightly lighter than air, helium relative density 7. |
| 6. Does not have allotropic modifications. | 6. Dielectric, poorly conducts heat. |
| 7. Included in various salts - nitrates (KNO 3, NaNO 3, Ca (NO 3) 2). | 7. t bale = -195.8 °С; t pl \u003d -210.0 ° С. |
| 8. Mass fraction in ammonia 82.35%, is part of proteins, amines, DNA. | 8. Dielectric constant 1.00. |
| 9. The mass of an atom is (for 14 N) 14u or 2.324 10 −23 g. | 9. Dipole moment is 0. |
| 10. The structure of the atom: 7p, 7e, 7n (for 14 N), electronic configuration 1s 2 2s 2 2p 3, two electron layers, five valence electrons, etc. | 10. Has a molecular crystal lattice (in the solid state). |
| 11. In the periodic system, it is in the 2nd period and VA-group, belongs to the family of p-elements. | 11. In the atmosphere, the volume fraction is 78%. |
| 12. Ionization energy 1402.3 kJ/mol, electron affinity −20 kJ/mol, electronegativity 3.07. | 12. World production 44 · 10 6 tons per year. |
| 13. Shows covalencies I, II, III, IV and oxidation states -3, -2, -1, 0, +1, +2, +3, +4, +5. | 13. Get: in the laboratory - by heating NH 4 NO 2; in industry - by heating liquefied air. |
| 14. Atomic radius (orbital) 0.052 nm. | 14. Chemically inactive, when heated, interacts with oxygen, metals. |
| 15. Main line in the spectrum 399.5 nm. | 15. Used to create an inert atmosphere when drying explosives, when storing valuable paintings and manuscripts, to create low temperatures (liquid nitrogen). |
| 16. The body of an average person (body weight 70.0 kg) contains 1.8 kg of nitrogen. | |
| 17. As part of ammonia, it participates in the formation of a hydrogen bond. |
Example 1.2. Indicate in which of the following statements oxygen is mentioned as a chemical element:
- a) the mass of an atom is 16u;
- b) forms two allotropic modifications;
- c) the molar mass is 32 g/mol;
- d) poorly soluble in water.
Decision. Statements c), d) refer to a simple substance, and statements a), b) - to the chemical element oxygen.
Answer: 3).
Each chemical element has its own symbol - a chemical sign (symbol): K, Na, O, N, Cu, etc.
A chemical sign can also express the composition of a simple substance. For example, the symbol for the chemical element Fe also reflects the composition of the simple substance iron. However, the chemical symbols O, H, N, Cl denote only chemical elements; simple substances have the formulas O 2 , H 2 , N 2 , Cl 2 .
As already noted, in most cases the names of chemical elements and simple substances are the same. The exceptions are the names of allotropic modifications of carbon (diamond, graphite, carbine, fullerene) and one of the modifications of oxygen (oxygen and ozone). For example, when we use the word "graphite", we mean only a simple substance (but not a chemical element) carbon.
The prevalence of chemical elements in nature is expressed in mass and mole fractions. Mass fraction w is the ratio of the mass of atoms of a given element to the total mass of atoms of all elements. Mole fraction χ - the ratio of the number of atoms of a given element to the total number of atoms of all elements.
In the Earth's crust (a layer about 16 km thick), oxygen atoms have the largest mass (49.13%) and mole (55%) fractions, silicon atoms are in second place (w (Si) = 26%, χ(Si) = 16 .35%. In the Galaxy, almost 92% of the total number of atoms are hydrogen atoms, and 7.9% are helium atoms. Mass fractions of atoms of the main elements in the human body: O - 65%, C - 18%, H - 10%, N - 3%, Ca - 1.5%, P - 1.2%.
The absolute values of the atomic masses are extremely small (for example, the mass of an oxygen atom is on the order of 2.7 ⋅ 10 −23 g) and are inconvenient for calculations. For this reason, a scale of relative atomic masses of elements was developed. At present, 1/12 of the mass of an atom of the nuclide C-12 is accepted as a unit of measurement of relative atomic masses. This value is called constant atomic mass or atomic mass unit(a.m.u.) and has the international designation u:
m u = 1 a. e.m. = 1 u = 1/12 (m a 12 C) =
1.66 ⋅ 10 - 24 g = 1.66 ⋅ 10 - 27 kg.
It is easy to show that the numerical value of u is 1/N A:
1 u = 1 12 m a (12 C) = 1 12 M (C) N A = 1 12 12 N A = 1 N A =
1 6.02 ⋅ 10 23 = 1.66 ⋅ 10 − 24 (d).
Relative atomic mass of an element A r (E) is a physical dimensionless quantity that shows how many times the mass of an atom or the average mass of an atom (for isotopically pure and isotopically mixed elements, respectively) is greater than 1/12 of the mass of an atom of the C-12 nuclide:
A r (E) \u003d m a (E) 1 a. e. m. \u003d m a (E) 1 u. (1.1)
Knowing the relative atomic mass, one can easily calculate the mass of an atom:
m a (E) \u003d A r (E)u \u003d A r (E) ⋅ 1.66 ⋅ 10 −24 (g) \u003d
A r (E) ⋅ 1.66 ⋅ 10 −27 (kg).
Molecule. And he. Substances of molecular and non-molecular structure. chemical equation
When atoms interact, more complex particles are formed - molecules.
Molecule - the smallest electrically neutral isolated set of atoms capable of independent existence and being the carrier of the chemical properties of a substance.
Molecules have the same qualitative and quantitative composition as the substance they form. The chemical bond between atoms in a molecule is much stronger than the forces of interaction between molecules (that is why the molecule can be considered as a separate, isolated particle). In chemical reactions, molecules, unlike atoms, are not preserved (destroyed). Like an atom, a single molecule does not have such physical properties of a substance as color and smell, melting and boiling points, solubility, thermal and electrical conductivity, etc.
We emphasize that the molecule is precisely the carrier of the chemical properties of the substance; it cannot be said that a molecule retains (has exactly the same) chemical properties of a substance, since the chemical properties of a substance are significantly affected by intermolecular interaction, which is absent for a separate molecule. For example, the substance trinitroglycerin has the ability to explode, but not a single molecule of trinitroglycerin.
An ion is an atom or group of atoms that has a positive or negative charge.
Positively charged ions are called cations, and negatively charged anions. Ions are simple, i.e. monatomic (K +, Cl -), and complex (NH 4 +, NO 3 -), one - (Na +, Cl -) and multiply charged (Fe 3+, PO 4 3 -).
1. For a given element, a simple ion and a neutral atom have the same number of protons and neutrons, but differ in the number of electrons: the cation has fewer of them, and the anion has more than the electrically neutral atom.
2. The mass of a simple or complex ion is the same as the mass of the corresponding electrically neutral particle.
It should be borne in mind that not all substances are composed of molecules.
Substances made up of molecules are called substances of molecular structure. It can be both simple (argon, oxygen, fullerene) and complex (water, methane, ammonia, benzene) substances.
All gases and almost all liquids have a molecular structure (the exception is mercury); solids can have both molecular (sucrose, fructose, iodine, white phosphorus, phosphoric acid) and non-molecular structures (diamond, black and red phosphorus, carborundum SiC, common salt NaCl). In substances of molecular structure, the bonds between molecules (intermolecular interaction) are weak. When heated, they are easily destroyed. It is for this reason that substances of a molecular structure have relatively low melting and boiling points, are volatile (as a result, they often have an odor).
Substances of non-molecular structure consist of electrically neutral atoms or simple or complex ions. Electrically neutral atoms consist, for example, of diamond, graphite, black phosphorus, silicon, boron, and salts, such as KF and NH 4 NO 3, of simple and complex ions. Metals are made up of positively charged atoms (cations). Carborundum SiC, silicon (IV) oxide SiO 2, alkalis (KOH, NaOH), most salts (KCl, CaCO 3), binary compounds of metals with non-metals (basic and amphoteric oxides, hydrides, carbides, silicides, nitrides, phosphides), intermetallic compounds (compounds of metals with each other). In substances of a non-molecular structure, individual atoms or ions are interconnected by strong chemical bonds, therefore, under normal conditions, these substances are solid, non-volatile, and have high melting points.
For example, sucrose (molecular structure) melts at 185 °C, and sodium chloride (non-molecular structure) melts at 801 °C.
In the gas phase, all substances are composed of molecules, and even those that at ordinary temperature have a non-molecular structure. For example, NaCl, K 2 , and SiO 2 molecules were found in the gas phase at high temperatures.
For substances that decompose when heated (CaCO 3, KNO 3, NaHCO 3), molecules cannot be obtained by heating the substance
Molecular substances form the basis of the organic world, and non-molecular substances form the basis of the inorganic (mineral) world.
Chemical formula. formula unit. chemical equation
The composition of any substance is expressed using a chemical formula. Chemical formula- this is an image of the qualitative and quantitative composition of a substance using the symbols of chemical elements, as well as numerical, alphabetic and other signs.
For simple substances of a nonmolecular structure, the chemical formula coincides with the sign of the chemical element (for example, Cu, Al, B, P). In the formula of a simple substance of a molecular structure, indicate (if necessary) the number of atoms in a molecule: O 3, P 4, S 8, C 60, C 70, C 80, etc. Noble gas formulas are always written with one atom: He, Ne, Ar, Xe, Kr, Rn. When writing the equations of chemical reactions, the chemical formulas of some polyatomic molecules of simple substances can (unless otherwise stated) be written as symbols of elements (single atoms): P 4 → P, S 8 → S, C 60 → C (this cannot be done for ozone O 3, oxygen O 2, nitrogen N 2, halogens, hydrogen).
For complex substances of molecular structure, there are empirical (simple) and molecular (true) formulas. Empirical formula shows the smallest integer ratio of the number of atoms in a molecule, and molecular formula is the true integer ratio of atoms. For example, the true formula of ethane is C 2 H 6, and the simplest is CH 3. The simplest formula is obtained by dividing (reducing) the number of atoms of the elements in the true formula by any suitable number. For example, the simplest formula for ethane was obtained by dividing the numbers of C and H atoms by 2.
The simplest and true formulas may either coincide (methane CH 4, ammonia NH 3, water H 2 O), or not coincide (phosphorus (V) oxide P 4 O 10, benzene C 6 H 6, hydrogen peroxide H 2 O 2, glucose C 6 H 12 O 6).
Chemical formulas allow you to calculate the mass fractions of atoms of elements in a substance.
The mass fraction w of the atoms of the element E in a substance is determined by the formula
w (E) = A r (E) ⋅ N (E) M r (B) , (1.2)
where N (E) - the number of atoms of the element in the formula of the substance; M r (B) is the relative molecular (formula) mass of the substance.
For example, for sulfuric acid M r (H 2 SO 4) = 98, then the mass fraction of oxygen atoms in this acid
w (O) \u003d A r (O) ⋅ N (O) M r (H 2 SO 4) \u003d 16 ⋅ 4 98 ≈ 0.653 (65.3%) .
According to formula (1.2), the number of element atoms in a molecule or formula unit is found:
N (E) = M r (B) ⋅ w (E) A r (E) (1.3)
or molar (relative molecular or formula) mass of a substance:
M r (V) \u003d A r (E) ⋅ N (E) w (E) . (1.4)
In formulas 1.2–1.4, the values of w (E) are given in fractions of a unit.
Example 1.3. In some substance, the mass fraction of sulfur atoms is 36.78%, and the number of sulfur atoms in one formula unit is two. Specify the molar mass (g/mol) of the substance:
Decision . Using formula 1.4, we find
M r = A r (S) ⋅ N (S) w (S) = 32 ⋅ 2 0.3678 = 174 ,
M = 174 g/mol.
Answer: 2).
The following example shows how to find the simplest formula of a substance from the mass fractions of elements.
Example 1.4. In some chlorine oxide, the mass fraction of chlorine atoms is 38.8%. Find the formula for oxide.
Decision . Since w (Cl) + w (O) = 100%, then
w (O) \u003d 100% - 38.8% \u003d 61.2%.
If the mass of a substance is 100 g, then m (Cl) = 38.8 g and m (O) = 61.2 g.
Let's represent the oxide formula as Cl x O y . We have
x : y = n (Cl) : n (O) = m (Cl) M (Cl) : m (O) M (O) ;
x : y = 38.8 35.5 : 61.2 16 = 1.093 : 3.825 .
Dividing the numbers obtained by the smallest of them (1.093), we find that x: y \u003d 1: 3.5 or, multiplying by 2, we get x: y \u003d 2: 7. Therefore, the oxide formula is Cl 2 O 7.
Answer: Cl 2 O 7.
For all complex substances of a non-molecular structure, chemical formulas are empirical and reflect the composition of not molecules, but the so-called formula units.
formula unit(FU) - a group of atoms corresponding to the simplest formula of a substance of a non-molecular structure.
Thus, the chemical formulas of substances of a nonmolecular structure are formula units. Examples of formula units: KOH, NaCl, CaCO 3 , Fe 3 C, SiO 2 , SiC, KNa 2 , CuZn 3, Al 2 O 3 , NaH, Ca 2 Si, Mg 3 N 2 , Na 2 SO 4 , K 3 PO 4 etc.
Formula units can be considered as structural units of non-molecular substances. For substances of molecular structure, these, obviously, are actually existing molecules.
Using chemical formulas, the equations of chemical reactions are written.
chemical equation- this is a conditional record of a chemical reaction using chemical formulas and other signs (equal, plus, minus, arrows, etc.).
The chemical equation is a consequence of the law of conservation of mass, so it is drawn up so that the number of atoms of each element in its both parts is equal.
The numbers in front of the formulas are called stoichiometric coefficients, while the unit is not written, but is implied (!) and taken into account when calculating the total sum of stoichiometric coefficients. Stoichiometric coefficients show in what molar ratios the starting substances react and the reaction products are formed. For example, for a reaction whose equation is
3Fe 3 O 4 + 8Al \u003d 9Fe + 4Al 2 O 3
n (Fe 3 O 4) n (Al) \u003d 3 8; n (Al) n (Fe) = 8 9 etc.
In reaction schemes, the coefficients are not placed and an arrow is used instead of an equal sign:
FeS 2 + O 2 → Fe 2 O 3 + SO 2
The arrow is also used when writing the equations of chemical reactions involving organic substances (so as not to confuse the equal sign with a double bond):
CH 2 \u003d CH 2 + Br 2 → CH 2 Br–CH 2 Br,
as well as the equations of electrochemical dissociation of strong electrolytes:
NaCl → Na + + Cl - .
Law of constancy of composition
For substances of molecular structure, law of constancy of composition(J. Proust, 1808): any substance of molecular structure, regardless of the method and conditions of preparation, has a constant qualitative and quantitative composition.
It follows from the law of composition constancy that elements in molecular compounds must be in strictly defined mass proportions, i.e. have a constant mass fraction. This is true if the isotopic composition of the element does not change. For example, the mass fraction of hydrogen atoms in water, regardless of the method of its production from natural substances (synthesis from simple substances, heating of copper sulfate CuSO 4 5H 2 O, etc.), will always be 11.1%. However, in water obtained by the interaction of deuterium molecules (hydrogen nuclide with A r ≈ 2) and natural oxygen (A r = 16), the mass fraction of hydrogen atoms
w (H) = 2 ⋅ 2 2 ⋅ 2 + 16 = 0.2 (20%) .
Substances subject to the law of composition constancy, i.e. molecular substances are called stoichiometric.
Substances of non-molecular structure (especially carbides, hydrides, nitrides, oxides and sulfides of metals of the d-family) do not obey the law of composition constancy, therefore they are called non-stoichiometric. For example, depending on the production conditions (temperature, pressure), the composition of titanium(II) oxide is variable and varies within TiO 0.7 -TiO 1.3, i.e. in a crystal of this oxide, there can be from 7 to 13 oxygen atoms per 10 titanium atoms. However, for many substances of a nonmolecular structure (KCl, NaOH, CuSO 4), the deviations from the constancy of the composition are very small, so we can assume that their composition is practically independent of the method of preparation.
Relative molecular and formula weight
To characterize substances of molecular and non-molecular structure, respectively, the concepts of "relative molecular weight" and "relative formula weight" are introduced, which are denoted by the same symbol - M r
Relative molecular weight- dimensionless physical quantity, which shows how many times the mass of the molecule is greater than 1/12 of the mass of the atom of the nuclide C-12:
M r (B) = m mol (B) u . (1.5)
Relative formula weight- dimensionless physical quantity, which shows how many times the mass of the formula unit is greater than 1/12 of the mass of the atom of the C-12 nuclide:
M r (B) = m FU (B) u . (1.6)
Formulas (1.5) and (1.6) allow you to find the mass of a molecule or PU:
m (say, PU) = uM r . (1.7)
In practice, the values of M r are found by summing the relative atomic masses of the elements that form a molecule or formula unit, taking into account the number of individual atoms. For example:
M r (H 3 PO 4) = 3A r (H) + A r (P) + 4A r (O) =
3 ⋅ 1 + 31 + 4 ⋅ 16 = 98.
The founder of "atomism" - a philosophical doctrine, according to which all elements of animate and inanimate nature consist of atoms (chemically indivisible particles). Atoms exist forever and are so small that they cannot be measured, they are the same and differ only in appearance, but retain all the properties of the original substance.
In 1808 he revived atomism and proved that atoms are real. Atoms are chemical elements that cannot be created anew, divided into smaller components, destroyed by any chemical transformations. Any chemical reaction only changes the order of rearrangement of atoms.
In 1897, the scientist J. Thompson proved the existence of electrons - negatively charged particles. In 1904, he proposed a model of the atom - "raisin pudding" An atom is a positively charged body, inside which small particles with a negative charge are distributed, like raisins in a pudding.
1911 - Together with his students, he conducted an experiment that refuted the theory of J. Thompson and proposed a model of the atom like a planetary system. In the center of the atom there is a positively charged nucleus, around which negatively charged electrons rotate. In this case, the main mass of the atom is concentrated in the nucleus, the mass of electrons is very small. The total charge of the nucleus and electrons must be equal to zero, since the atom as a whole is electrically neutral.
Particle Mass Charge Absolute (kg) Relative Electric Relative Electron 9.109* .00051.602* Proton 1.673* .602* Neutron 1.675* Z - proton number (shows the number of protons in the nucleus and their total mass (relative)) N - neutron number (shows the number of neutrons in the nucleus and their total mass (relative)) A - mass (nucleon) number - this is the sum of neutrons and protons in the nucleus and their total mass (relative))
Nucleon number (equal to the relative atomic mass) - Proton number (equal to the ordinal number of the element) A = 23 Z = 11 N = = 12 e = 11
OPTION 1 1) An atom is a particle consisting of ...... 2) The mass of an atom is determined by the sum of the masses of the particles: ... 3) The serial number of the element shows the number ... .. and the number ... .. in the atom 4) Atoms of one chemical element that differ in relative value atomic mass is called ……. 5) The type of atoms with a certain nuclear charge is called .... 6) Write down the composition of the zinc atom using symbols (protons, neutrons, electrons, nucleon number) OPTION 2 1) The atomic nucleus consists of .... 2) Isotopes differ in quantity ... .. 3) The mass number of an atom is the sum of the masses of particles .... 4) Number .... = number.... = the ordinal number of the element. 5) An electron is denoted by the symbol ..., has a charge ...., and a relative mass .... 6) Write down the composition of the copper atom using symbols (protons, neutrons, electrons, nucleon number)
