Is BaSO4 an ionic or covalent bond



Salts are chemical compounds that are made up of positively charged ions, the so-called cations, and negatively charged ions, the so-called anions. Ionic bonds exist between these ions. Almost all compounds with this type of bond are called salts. At inorganic salts the cations are often formed by metals and the anions are often formed by non-metals or their oxides. As a solid, they together form a crystal lattice. As organic salts refers to all compounds in which at least one anion or cation is an organic compound. Connections where all cations or. all anions of protons (H.+) or hydroxides (OH) are not called salts, because their effect as an acid or base is in the foreground.

Inorganic salts

In the narrowest sense, salt is sodium chloride (NaCl, table salt). In a broad sense, all compounds that are built up from anions and cations like NaCl are called salts. Sodium chloride is made up of the cations Na+ and anions Cl built up. The salt calcium chloride (CaCl2) is from approx2+ and Cl educated. The formulas NaCl and CaCl2 are the ratio formulas of the compounds (Na: Cl = 1: 1, or Ca: Cl = 1: 2). The ratio formula of a salt is determined by the number of charges of the ions, since positive and negative charges have to compensate each other. Ratio formulas are in clear contrast to formulas of individual compounds such as water (H.2O) or methane (CH4) that are molecules. In the case of inorganic salts, ionic bonds exist between the ions. A very large number of ions form an ion lattice with a specific crystal structure, if the respective ratio formula is adhered to. The figure on the right shows a small excerpt from the structure of sodium chloride. Since there are many different cations and anions, a large number of different salts are known. Some of the ions are listed in the tables below. Unlike the halide Cl, other non-metals form oxidic anions. Nitrogen can, among other things, the nitrate anion (NO3) form. The sulfate anion (SO42−) is also an oxidic anion, but carries two negative charges. In the case of oxidic anions, the oxygen is firmly bonded to the other element involved with covalent bonds. Ionic bonds exist only between the anions and cations. Sodium nitrate (NaNO3), among the sulfates sodium sulfate (Na2SO4) known. The cations are mostly formed by metals. They can be monovalent or polyvalent, i.e. they can carry one or more positive charges. Salts formed by metal cations are sometimes called Metal salts.

Examples of cations and anions

Anions
monovalent bivalent oxidic metallic
Fluoride, F.Oxides, O2−Carbonates, CO32−Chromates, CrO42−
Chlorides, ClSulfides, S.2−Sulfates, SO42−Permanganate, MnO4
Bromide, BrPhosphates, PO43− complex
Iodides, I.Nitrates, NO3Hexacyanoferrate (II), [FeII(CN)6]4−

Properties of salts

 

  • Many salts are solids at room temperature with relatively high melting points. Many salts are quite hard and brittle and have smooth breaking edges when mechanically processed. These properties are quite typical for solids that are built up by an ion lattice and therefore form crystals. But not every crystalline substance is a salt. So sugar (sucrose) also forms crystals, but has no Ion lattice and counts Not to the salts.
  • Many salts are soluble in water and almost always insoluble in organic solvents. In the case of water-soluble salts, the water overcomes the lattice energy of the ion lattice by hydration. If the hydration energy is similar to or greater than the lattice energy, the salt is moderately or readily soluble. In solutions, the individual ions are surrounded by water molecules quite tightly and intensively. As a reaction, this is often represented in chemistry as follows:

    The (s) indicates a solid and (aq) indicates that the ion is hydrated.
  • Dissolving salts in water can change the pH of the respective solution. If the salt does not affect the value, one speaks of neutral salts. Sodium chloride is also one of the neutral salts. Other salts raise or lower the pH. One speaks of basic or. acid salts. How a certain salt reacts can only be estimated with difficulty from the composition of the compound. In principle, however, the following applies: Anions (acid residues) from strong acids usually react neutrally. Acid residues from weak acids usually have a basic reaction. The behavior of phosphates is an example of salts, of which polyprotonic acids are known.
  • Dry salt crystals are electrical insulators. Salt melts and aqueous solutions, on the other hand, conduct the electrical current due to their freely moving ions as charge carriers; they are electrolytes.

Other cations and anions

  • However, ions formed from non-metals also exist among the cations. The ammonium cation (NH4+), for example, forms the salt ammonium sulfate ((NH4)2SO4). There are organic compounds analogous to ammonium compounds (quaternary ammonium compounds), which are described in more detail below.
  • The proton (H.+) occur as a cation, e.g. B. the salt sodiumhydrogensulfate (NaHSO4). Are only H+-Ions are present, one no longer speaks of salts. In the case of sulfates, the compound would only be sulfuric acid with protons (H.2SO4). Analogous salts are also known among the phosphates: sodium phosphate, disodiumhydrogenphosphate, sodiumdihydrogenphosphate. If only protons are present, the compound is called phosphoric acid (H.3PO4).
  • Metal oxides make up a large part of the earth's crust and can also be viewed as salts. The anion O2− However, (oxide ion) occurs as such only with salts in the molten state; it is not known in the solid state or in their aqueous solutions. The metal (M) is preferably assigned an oxidation number (valence) instead of speaking of cations. One speaks of one-, two-, three- and polyvalent metals (MI., MII, MIII). The oxide ion has the valence O-II assigned. The valency of the metals thus determines the ratio formula of the respective compound: MI.2O, MIIO, MIII2O3. If an oxide is considered "soluble", a specific chemical reaction takes place, for example:

    Sodium oxide reacts with water to form hydroxide ions to form caustic soda.
    Calcium oxide (CaO) reacts similarly, too quick lime called, too slaked lime (Ca (OH)2). Very many oxides do not react with water. The iron (III) oxide (Fe2O3) (Rust) is not a water-soluble compound.
  • Sulphides. Minerals are often found in nature as sulfides (p2−) to find, e.g. B. pyrite and copper luster. Sulphides can also be viewed as salts. Sodium sulfide (Na2S) is a soluble salt, most sulfides, such as zinc sulfide (ZnS) and copper (II) sulfide (CuS), are practically insoluble in water. In analytical chemistry, the different (poor) solubility of different metal sulfides is used to separate the elements (in the separation process of the hydrogen sulfide group).
  • Some transition metals can form not only cations but also anions as oxides. So chromium can convert the chromates ([CrO4]2−), the anion in potassium chromate (K2[CrO4]) and manganese the permanganates ([MnO4]), the anion in potassium permanganate (K [MnO4]) form.

 

  • As complex salts one denotes salts, in which with the participation of Molecules independent (stable) ions are present - in contrast to ions such as [CrO4]2−made up of atoms. In the case of potassium hexacyanoferrate (II) (K4[Fe (CN)6]) forms the iron ion Fe2+ together with six cyanide groups (CN) together form a stable anion with four negative charges. The hexacyanoferrate (II) anion is therefore one of the complexes. In the salt there are ionic bonds between potassium ions and the hexacyanoferrate (II) anion. Similarly, the iron ion forms Fe3+Potassium hexacyanoferrate (III) (K3[Fe (CN)6]) also a complex salt. At K3[Fe (CN)6] forms the iron ion Fe3+ together with six cyanide groups (CN) together form a stable anion with three negative charges.

Crystal water

In addition to the ions, many salts also contain water molecules in certain quantities, the so-called crystal water. It is specified in the ratio formula, as in the example of sodium sulfate decahydrate: Na2SO4 · 10 H.2O.

Double salts

In addition to salts with only one type of cation (M), salts with two different cations are also known. These salts are called double salts, like alums with the general composition MI.M.III(SO4)2. Example: aluminum potassium sulfate dodecahydrate (KAl (SO4)2 · 12 H.2O).

Limits of the term Salts

  • Substances are called salts if there are ionic bonds between the particles of the compound. However, it is not easy to determine whether this type of bond exists. While calcium oxide (CaO) has ionic bonds, chromium (VI) oxide (CrO3) only covalent bonds between Cr and O; it should therefore no longer be called salt. For this reason it is often more clever to use oxides not from salts, but generally from Metal oxides to speak.
  • Salts are usually understood as chemical compounds because they have a defined composition of different chemical elements. However, mixed crystals are known from two salts which are not composed stoichiometrically: Thus potassium permanganate (K [MnO4]) with barium sulfate (Ba [SO4]) mixed crystals in almost any proportions (even if only up to a certain maximum of barium sulfate), since the components have similar crystal structures and lattice spacings. A chemical similarity of the compounds involved or an equal valency is not absolutely necessary for the formation of mixed crystals.

Organic salts

In addition to the inorganic salts described above, there are also numerous salts of organic compounds. The anions of these salts are derived from the organic acids. The salts of the carboxylic acids are important here, such as acetic acid, many of which are known as salts Acetates (CH3COO) are known. So with Na+ the salt sodium acetate or with Cu2+ form the copper acetate. Acetic acid is a monocarboxylic acid (has only one -COOH group) and only forms monovalent anions. Citric acid is a tricarboxylic acid (has three -COOH groups) and can form trivalent anions; their salts are called citrates. For example, the salts sodium citrate and calcium citrate are known. Many acetates and citrates form crystals, but that is not the real reason for calling them salts. The real and only reason is due to the presence of ionic bonds between anions and cations. Covalent bonds exist within the ions of organic compounds.

The salts of carboxylic acids, which are among the fatty acids, are of practical importance. The sodium or potassium salts of fatty acids are called soaps. Mixtures of different fatty acid salts are present in soaps. They find practical use as curd soap or soft soap. As a concrete example, palmitic acid forms salts, which Palmitates to be named. Salts based on such large organic molecules are usually not crystalline.

Analogous to the inorganic sulfates (SO42−) there are also organic sulfates (R-O-SO3), such as sodium lauryl sulfate, which are used as surfactants in shampoos and shower gels. Salts, the alcoholates, of alcohols are also known. Alcohols are extremely weak acids and are therefore almost never called that. Compounds of the form R-OM.+ (M = metal) win. In analogy to many inorganic oxides (MO), alcoholates react with hydrolysis on contact with water and the corresponding alcohols are formed.

Among the organic cations, the ammonium cations (NH4+) analog connections meaning. They are commonly called quaternary ammonium compounds. In these compounds, the nitrogen atom usually carries four alkyl groups (R-) and one positive charge. For example, the alkylammonium compound cetyltrimethylammonium bromide is an organic ammonium compound in which a bromine atom is present as an anion. Ammonium compounds with three short and one long alkyl groups are of practical importance, since these cations show the properties of surfactants in aqueous solution. Compounds of this type also play an important role in the metabolism of living things, such as B. the choline.

In principle, every organic amine can be absorbed by a proton (H.+) become a cation. Analogous to the reaction of ammonia (NH3) to the ammonium ion (NH4+), for example, a primary amine (R-NH2; R = organic residue) to the cation R-NH3+. Since such compounds are usually more polar and therefore more easily soluble in water than the original substances, nitrogen-containing active pharmaceutical ingredients, for example, are converted into salts, the so-called hydrochlorides, by adding hydrochloric acid. This makes it easier for them to be absorbed into the body. In contrast to the original compounds, hydrochlorides can also be more easily purified by recrystallization.

In addition to molecules that have a positive or Carrying negative charge, there are also molecules that have a negative and have a positive charge. They are called Internal salts or Zwitterions. The betaine group of substances is one of the inner salts, the simplest compound of which is betaine.

The amino acids have a carboxyl group (-COOH) and an amino group (-NH2) and can react acidic and basic. An anionic (-COO) and a cationic (-NH3+) Group and thus a zwitterion. The simplest amino acid is alanine, which is readily soluble in water. In contrast to other ions dissolved in water, zwitterions show poor (no) electrical conductivity. (Ampholyte)

Examples of organic cations and anions

Manufacture of inorganic salts

Reactions of acids and bases

Salts are formed when acids react with bases ((Greek: basis) Arrhenius: bases are the basis for salts). The oxonium ions of the acid and the hydroxide ions of the base form water (neutralization). Some salts are sparingly soluble in water and directly form the solid. As a rule, the salt is in solution and can be obtained as a solid by evaporating the water.

From other salts

Some salts can be obtained from two other salts. If you mix aqueous solutions of two salts, a third salt can form as a solid. This only works if the third salt, in contrast to the other two, is less soluble.

Reaction of oxides

As described above, metal oxides tend to form hydroxides with water. Acids can be used to neutralize oxonium ions to form water. Metal oxides that are “insoluble” (= stable) in pure water also react under acidic conditions. In this way, many salts, such as. B. win copper sulfate.

Other reactions

The ions in the reactions described above are not formed first, but exist before a new salt is formed. If no or not all ions with the required charge are present in reactions to form a new salt, redox reactions take place. In this way, salts can be obtained from elemental metals and non-metals. Reactions of this type are described in more detail under the salt formation reaction.

Categories: Fabric Group | salt