To form the molecules Of chemical compounds, the atoms of different substances or elements must combine with each other in a stable way. This can occur in various ways by virtue of the structural characteristics of every atom (consisting of a positively charged nucleus surrounded by a cloud of electrons).
The electrons have a negative charge and remain close to the nucleus because the electromagnetic force of the protons attracts them. The closer an electron is to the nucleus, the greater the energy required to get it released.
But not all elements are the same: some have a tendency to lose the outermost electrons of the cloud (elements with low ionization energy), while others tend to capture them (elements with high electron affinity). This happens because according to Lewis octet rule, stability is associated with the presence of 8 electrons in the outermost shell u orbital (region of space where it is most likely to find an electron around the atom), at least in most cases.
Due to this, to form the different chemical compounds, the neutral atoms give up, accept or share the electrons of their last electronic shell, always ensuring that there are 8 electrons left in it, although there are always exceptions, such as the case of hydrogen that can only have 2 electrons.
So, as the neutral atoms they can gain or lose electrons, ions of opposite charge can be formed. The electrostatic attraction between the oppositely charged ions causes the ions to bond together and form chemical compounds, in which one of the elements gave up electrons and the other received them. So that this can happen and a ionic bond it is necessary that there exists a difference or delta of electronegativity between the elements involved of at least 1.7.
The ionic bond, in general, occurs between a metallic compound and a non-metallic one: the metal atom gives up one or more electrons and, consequently, forms positively charged ions (cations), and the nonmetal gains them and passes to be the negatively charged particle (anion). The alkali metals and the alkaline earths they are the elements that have more tendency to form cations, and halogens and oxygen are those that usually constitute anions.
In general, the compounds that are formed by ionic bonds are crystalline solids at room temperature, insoluble in water and with a high melting point, in case the attractions between their ions are strong. On the other hand, when the attraction between their ions is weaker, they have lower melting points and are soluble in water.
In solution they are very good electricity conductors since they are strong electrolytes, that is, they ionize easily forming anions and cations that can carry electrical charges. On the other hand, the lattice energy of an ionic solid is what marks the attractive force between the ions of that solid.
It is important to clarify that there is neither a completely ionic bond nor a completely covalent bond (which occurs between two atoms that share the electrons of their last energy level or layer). Actually, both types of links have a percentage of each. Some scientists consider ionic bonding to be an exaggeration of covalent bonding.
Examples of ionic bonds
- Magnesium oxide (MgO)
- Copper (II) sulfate (CuSO4)
- Potassium Iodide (KI)
- Zinc hydroxide (Zn (OH)two)
- Sodium chloride (NaCl)
- Silver nitrate (AgNO3)
- Lithium Fluoride (LiF)
- Magnesium chloride (MgCltwo)
- Potassium hydroxide (KOH)
- Calcium nitrate (Ca (NO3)two)
- Potassium dichromate (KtwoCrtwoOR7)
- Disodium phosphate (NatwoHPO4)
- Iron (III) sulfide (FetwoS3)
- Potassium bromide (KBr)
- Calcium carbonate (CaCO3)
- Sodium hypochlorite (NaClO)
- Potassium sulfate (KtwoSW4)
- Manganese (II) chloride (MnCltwo)
- Calcium phosphate (Ca3(PO4)two)