Formation of Ionic Compounds - Their Properties and Structures

You might be wondering what happens when metals and non-metals react? Well, they form ionic bonds which form ionic compounds. An ionic bond refers to an electrostatic force of attraction between two atoms having opposite charges. An ionic bond occurs when a transfer of an electron from a metal to a non-metal takes place. An ionic bond takes place between cations and anions. 

Anions are ions having a negative charge and cations have a positive charge. You might not be familiar with the terminology and concepts of an ionic compound but fret not, as we have got you all covered. In this article, you can learn about the ionic compound, its structure, formation, and frequently asked questions. 

What is an Ionic Compound?

You must know that each atom is unique due to its particular number of protons, neutrons, and electrons. Typically, the number of protons and electrons are equivalent to an atom. The number of protons in an atom never changes because it would mean having an entirely different element. However, the number of electrons in an atom can change. 

So, when an atom gains or loses an electron, you can get an ion. As the electrons already have a net negative charge, the charge of an atom changes when the electron gets added or removed from it. It happens because the number of electrons is no longer in sync with the protons, which have a positive charge.

Atoms that gain an electron and thus, obtain a net negative charge are nothing but anions. In contrast, atoms that lose electrons and thus, obtain a net positive charge, get called cations. Anions tend to be non-metals while cations tend to be metals. Also, ions may refer to a single atom or multiple, complex group of atoms.

When it comes to ions, the opposites indeed attract. The opposite charges, positive and negative, hold together in ionic bonds, forming ionic compounds. As the name suggests, it is nothing but a compound made of ions. The loss or gain of one atom matches the loss or gain of the other. So, the atom donates an electron to the atom that needs it, and they form a pair.

You can consider ions as a two-bar magnet. When you try to put the south end and north end of the different magnets together, they repel each other. But, if you turn around one of the magnets, then you’re putting the north end to a sound end and magnets instantly snap together. Ions show similar behaviour, one positive and one negative ion join together to make an ionic compound. 

Sodium Chloride, also generally known as common salt, is a well-known ionic compound.

Cation

In cation, the number of electrons is less compared to the number of protons forming a net positive charge. For the formation of a cation, an element has to lose one or more electrons which might be pulled by another element having a strong affinity towards them. A ‘+’ sign is used to denote a cation. Example: Mg₂⁺

Anion

In an anion, the number of electrons is more compared to the number of protons forming a net negative charge. For the formation of an anion, an element has to gain one or more electrons which might be lost by another element having a weaker affinity towards them. A ‘-’ sign is used to denote a cation. Example: O₂⁻.

Properties of the Ionic Compound

• Physical Properties: There is a strong force of attraction between positive and negative ions, which makes ionic compounds solid and not easily breakable. However, they break into pieces upon applying pressure, and that’s why they are brittle.

• Melting and Boiling Points: Ionic compounds have a significant force of attraction between them. So, it requires a large amount of energy to break the ionic bonds between the atoms. That’s why ionic compounds have a higher melting and boiling point.

• Solubility: Ionic compounds can dissolve in polar solvents. Water, methanol, and formamide are some examples of polar solvents. Also, ionic compounds are insoluble or barely soluble in non-polar solvents like chloroform, hydrocarbons, etc.

• Electric Conductivity: Ionic compounds don’t conduct electricity in solid states, but they do conduct in the molten state. As you know, the conduction of electricity involves a transfer of charge from one point to another.

• In solid-state, the movement of ions is not possible, and thus, ionic compounds can’t conduct electricity. However, ionic compounds in the molten state can conduct electricity because their electrostatic forces of attraction get overcome by the heat released.  

• They are brittle in nature.

Structure of Ionic Compound 

The structure of an ionic compound relies on the relative size of the cations and anions. Ionic compounds include salts, oxides, sulfides, hydroxides, and most inorganic compounds. Ionic solids get held together by the electrostatic forces of attraction between positive and negative ions. 

When sodium ions attract chloride ions and vice versa, you get a 3-D structure of Na+ and Cl- ions. It’s nothing but a crystal of sodium chloride. The structure doesn’t have any charge because there are equal numbers of sodium and chloride ions. The forces of attraction between ions hold the structure in place. Below is a figure to demonstrate a sodium chloride structure.

Ionic character formula

Ionic character is defined as a magnitude of charge separation in polar covalent bonds. It helps to find the difference in the electronegativity of the two atoms.

Δχ = χB − χA

As the difference in electronegativity increases, the bond polarity, and ionic character increase.

Example:

When Magnesium reacts with chlorine,

The outermost orbit of Mg has two electrons thus it loses those two electrons i.e two electrons from the M shell are removed and the L shell becomes the outermost orbit. Hence it forms a stable octet. Now, Mg has 12 protons but only 10 electrons; this gives Mg a positive charge, forming Mg₂⁺. 

Similarly, in the case of chlorine, the outermost orbit has seven electrons. Hence, Cl now is in need of 1 electron to complete its stable octet. Cl gains one electron from the Mg ion. But Mg has released two electrons and Cl needs only one electron so here the two atoms of Cl combine with one atom of Mg. Thus Cl develops a negative charge Cl⁻. This reaction forms MgCl₂.

Applications of ionic compounds

• NaCl (Sodium Chloride) is used in ordinary tablets.

• NaF ( Sodium Fluoride) IS used in the toothpaste that we use to brush our teeth.

• NaHCO₃ (Sodium bicarbonate) also known as baking soda is used in cooking and majorly in baking cakes, idlis, etc.

• Mg(OH)₂ (Magnesium hydroxide) is used as an antacid to treat acidity.

• K₃PO₂ (Potassium phosphate) is used as a food additive.

• MgSo₄ (magnesium sulfate) is used to purify water.

• Ionic compounds are also used to preserve the wood. Boric acid and oxides are commonly used.

• They are also used as growth regulators. Eg: gibberellic acid.

• Ionic compounds are resistant to organic solvents hence they are also used in paint pigmentation.

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