What are binary salts?
The binary salts are compounds formed primarily by the chemical bonding of a metallic element with low ionization potential, and a nonmetallic element with high electron affinity (electronegative). These types of chemical compounds are called ionic binary salts.
Meanwhile, molecular binary salts, also known as volatile salts, are a small group of binary salts formed by the union of two non-metallic elements with small differences in electronegativity.
The presence of the ionic bond is responsible for the characteristics and properties of ionic binary salts, such as their high melting and boiling points, their crystal formation, their hardness, etc.
An example of an ionic binary salt is sodium chloride, NaCl. Sodium represents the metallic element with the low ionization potential, while chlorine is the electronegative non-metallic element. NaCl has all the properties that can be expected for a binary salt.
In molecular binary salts, on the other hand, there is a covalent bond between the components of the salts. The covalent bond is weaker than the ionic one and this produces differences in the characteristics and properties of the molecular binary salts compared to the ionic ones. For example, the boiling and melting points of molecular binary salts are lower.
An example of a molecular binary salt is carbon tetrachloride, CCl 4, which is volatile and non-ionic. It is classified as such, even when it does not exhibit any of the properties expected for a salt: it is not solid, nor crystalline, nor is it composed of ions.
Characteristics of binary salts
Binary salts have a number of characteristics:
Ionic binary salts are formed by the union of an element from the group of metals, with an element belonging to the group of non-metals. Meanwhile, molecular binary salts are formed by the union between two non-metallic elements, other than oxygen and hydrogen.
The components of an ionic binary salt are linked by an ionic bond. Metals, although there are exceptions such as beryllium, are characterized by low ionization potentials. This allows them to easily release electrons and transform them into positively charged ions (cations).
Electrons released by metals are captured by nonmetal elements, due to their high affinity for electrons (electronegativity). This causes the nonmetal element present in the binary salt to become negatively charged (anion).
Due to the electrostatic interaction between the positive charge acquired by the metal present in the binary ionic salt, and the negative charge that appears in the nonmetal element, a high-energy ionic bond is formed between the components of the salt.
The non-metallic components of molecular binary salts are linked by a covalent bond, in which the two non-metallic elements share a pair of electrons.
Ionic binary salts acquire a crystalline structure, which is due to the strength of the ionic bond between the components of the salt. In the case of sodium chloride, it forms a cubic crystal.
Ionic binary salts in crystalline form are not conductive of electricity, therefore they are considered as electrical insulators. However, when the binary salt crystals dissolve in water they become good conductors of electricity.
This is because the electrical charges in ionic binary salts conduct electricity. Likewise, molten salts are good conductors of electricity.
Melting and boiling points
Due to the high energy content of the ionic bond present in ionic binary salts, their boiling and melting points are high. For example, sodium chloride has a melting point of 801 ° C, and a boiling point of 1413 ° C.
Molecular binary salts, on the other hand, have lower melting and boiling points than ionic ones.
Ionic binary salts with high-energy ionic bonds, such as those formed by alkali metals (lithium, sodium, potassium, rubidium, and cesium) are usually white and crystalline. This is the case with sodium chloride, which is white in color.
But if the bond that joins the components of the ionic binary salt has an ionic character of less intensity, the color of the salt can be yellow, orange, or red. In addition, the color of the ionic binary salt can depend on the degree of hydration that it possesses.
For example, cobalt (II) chloride (CoCl 2 ) has a blue color if the salt is in anhydrous form; but when cobalt chloride is in the hexahydrate form (CoCl 2 · 6 H 2 O) it acquires a reddish color.
Ionic binary salts are strong and hard due to the ionic bonds present in them. But they can become brittle under pressure.
This is due to the fact that deformation can occur in the structure of the salt that brings the electrical charges present in them closer together. Therefore, electrostatic repulsions are produced between the electric charges of the binary salt crystals, capable of causing them to break.
Ionic or neutral binary salts are the most numerous. They are represented by the formula MX, where M represents the metallic element, and X the non-metallic element, and they are named in the following ways:
First, the root of the non-metal element is placed, adding the suffix “uro”, followed by the word “de” and the name of metal. If the metal has a single valence, simply enter the name of the metal as is. For example, the salt of the formula KBr has named potassium bromide.
But if the metal has two valences, the name of the metal is usually changed to its Latin root, and the suffix “bear” is added to the root of the metal. If the highest valence is present in the metal, the suffix “ico” is used, and the preposition “de” is also deleted.
For example: in FeCl 2 the valence of iron is +2, which is why it is named ferrous chloride. While in FeCl 3 the valence of iron is +3, then the compound is named ferric chloride.
First, a numerical prefix is placed that can be di, tri, tetra, etc., which indicates the number of atoms of the non-metallic element in the binary salt, followed by the root of the name of the non-metal with the suffix “uro”. Then the preposition “of” is placed followed by a numerical prefix and the name of the metal.
For example, the compound of the formula AlCl 3 is named aluminum trichloride.
First, the root of the nonmetal name is placed followed by the suffix “uro”. Then the preposition “of” is placed and then the name of the metal is added. At the end of the metal name, its valence or oxidation state is placed in parentheses and in Roman numerals.
Example: CuCl 2 salt is named copper (II) chloride.
Nomenclature of molecular binary salts
Molecular binary salts are represented by the molecular formula X a Y b, where:
- X represents the least electronegative nonmetallic element.
- Y represents the most electronegative element.
- The subscripts a and b represent the valences of the non-metallic elements.
First, a numerical prefix is placed, if any, followed by the root of the most electronegative nonmetallic element, adding the suffix “uro”. Then the preposition “of” is placed followed by a numerical prefix and the name of the less electronegative nonmetallic element.
The molecular binary salt PCL 3 is named phosphorous trichloride.
How are binary salts formed?
Ionic binary salts can be formed by a neutralization reaction between an acid and a hydroxide. For example, potassium chloride can be formed from the reaction of hydrochloric acid (HCl) with potassium hydroxide (KOH), additionally, a water molecule is produced:
HCl + KOH → KCl + H 2 O
Metals, especially those belonging to the group of alkali metals, can react directly with the gases of electronegative non-metallic elements to form ionic binary salts.
When the solvent evaporates from a solution due to high temperatures, an increase in the concentration of the components of the ionic binary salts can occur, which favors their interaction and the nucleation process; that is, the formation of ionic bonds, a process that leads to the formation of ionic binary salt crystals.
Examples of binary salts
Ionic binary salts List
- NaCl: sodium chloride
- NaBr: sodium bromide
- NaI: sodium iodide
- NaF: sodium fluoride
- Na 2 S: sodium sulfide
- Na 3 P: sodium nitride
- LiF: lithium fluoride
- LiBr: lithium bromide
- Li 2 S: lithium sulfide
- Li 3 N: lithium nitride
- CuF: copper fluoride
- CuF 2 : copper difluoride
- CuBr: copper bromide
- Cu 2 S: dicopper sulfide
- Cu 3 N: tricobre nitride
- PbS: lead sulfide
- FeF 3 : iron trifluoride
- FeF 2 : iron difluoride
- FeCl 3 : iron trichloride
- PbF 4 : lead tetrafluoride
- PbS 2 : lead disulfide
- AlCl 3 : aluminum trichloride
- AlN: aluminum nitride
- AlP: aluminum phosphide
- MgCl 2 : magnesium dichloride
- MgF 2 : magnesium difluoride
- CaCl 2 : calcium dichloride
- CaF 2 : calcium difluoride
- CaS: calcium sulfide
- K 2 S: dipotassium sulfide
- KCl: potassium chloride
- K 3 N: potassium nitride
Molecular or volatile binary salts
- BCl 3: boron trichloride
- CS 2: carbon disulfide
- PCl 3: phosphorous trichloride
- CCl 4 : carbon tetrachloride
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