An ionic bond is a type of chemical bond between atoms, where one of them transfers an electron to the other . This bond is usually established between metals and non-metals with different electronegativity. Usually, the metal yields its electrons to the non-metal element.
This type of bond is produced by the attraction of ions with opposite charges. When yielding or accepting the valence electrons , the ions comply with the octet rule and, therefore, are more stable. Valence electrons are electrons from the outermost layer of the atom, which can participate in chemical bonds.
Characteristics of the ionic bond
- It is established between positively charged ions (cations) and negatively charged ions (anions).
- It is established between atoms with large electronegativity differences.
- An electron transfer occurs.
- It is usually found forming salts.
Properties of ionic compounds
- They tend to form brittle crystalline networks: at the atomic level, an ionic crystal has a regular three-dimensional structure, formed by the intercalated cation and anion.
- They are electrically neutral in their solid state.
- They have high boiling and melting points: the forces of attraction between the ions is greater so more energy is required to separate them
- They are solid at room temperature due to the high melting points.
- When they dissolve in water they are good conductors of electricity, while in the solid state they are poor conductors.
How is an ionic bond formed?
An atom that yields one or more electrons transforms into a positively charged ion or cation . Examples of cations are the sodium cation Na +1 , the cation calcium Ca +2 and the cation aluminum Al +3 . The ability to release electrons is characteristic of metals.
When ions with opposite charges come into contact, an electrostatic attraction occurs and the ionic bond is formed. For example, the sodium cation Na +1 forms an ionic bond with the fluoride anion F -1 and forms the sodium fluoride NaF.
An ionic bond is also formed when two atoms have a very large electronegativity difference. The electronegativity is the property of an atom to attract an electron . For example, between the barium Ba and the sulfur S, in the barium sulphide BaS, an ionic bond is formed.
Barium Ba has an electronegativity value of 0.89 (Pauling scale) and for sulfur S it is 2.58. This great difference in electronegativity explains why sulfur attracts more strongly the electrons of the barium.
Examples of ionic compounds
In general, all salts are ionic compounds. Let’s see some examples.
Potassium iodide KI is an ionic compound formed by the potassium metal cation K (K + 1 ) and the anion of the halogen iodine or iodide (I -1 ). It is used to prepare iodized salt and prevent hypothyroidism due to iodine deficiency in the diet. Its melting point is 681 ° C and the boiling point is 1,330 ° C.
The foam volcano is produced when the potassium iodide and oxygenated water react with liquid detergent.
Ammonium chloride NH 4 Cl is an ionic compound formed between the chloride Cl -1 and the ammonium cation NH 3 + . It has a boiling point of 520 ° C and a melting point of 338 ° C. It dissolves easily in water and is used predominantly as an agricultural fertilizer.
Iron oxide (II)
The iron oxide (II) is found in the mineral wustite. It has a melting point of 1377 ° C and its boiling point is 3414 ° C. It is black and should not be confused with rust, which is iron oxide (III) hydrated Fe 2 O 3 H 2 O. It is used as a pigment in tattoos.
Sodium chloride NaCl is the salt commonly used in our kitchens. It has a melting point of 801 ° C and a boiling point equal to 1465 ° C. In water, Na +1and chloride Cl -1 are easily dissociated in water .
Calcium oxide CaO (also known as quicklime) is formed when calcium Ca transfers the two electrons from its valence shell, remaining as Ca +2 , to oxygen, which transforms to O -2 . The CaO has a melting point of 2613 ° C and a boiling point of 2850 ° C. It is used in the construction industry mainly.