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Substances resulting from the chemical combination of two or more elements in fixed proportions are called compounds. Most elements do not exist in their free native state but are in the combinations of two or more elements as chemical compounds. In ionic compounds the constituent elements exist as ions. Ions are atoms or groups of atoms that carry a charge by virtue of losing or gaining one or more electrons.

Ionic compounds result from the combination of a positive ion known as a cation and a negative ion called an anion. Atoms in a compound are held together by covalent bonds. Bonds dictate how atoms are held together in a compound or molecule, but ionic compounds are composed of ions.

Ionic Compound Definition

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Definition of ionic compound

An ionic compound is composed of cations and anions joined together. Such compounds are held together by electrostatic forces, and adopt structures that maximize the attraction of oppositely charged species and minimize the repulsion between charged species with the same sign.

To define ionic compound in simple words "its a combination of metals with nonmetals."

Ionic Compound Formula

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Every ionic compound contains discrete ionic units with specific charges. In addition ionic compounds must always contain equal amounts of positive and negative charge. These requirements dictate the ratio of cations to anions in an ionic substance. The chemical formula of an ionic compound identifies its ionic units and the cation-to-anion ratio.

The following guidelines ensure uniformity in writing formulas for ionic compounds. The formula unit of an ionic compound shows the
  1. The cation is always listed before the anion.
  2. The formula of any polyatomic ion is written as a unit.
  3. Polyatomic ions are placed in parentheses with subscripts to indicate ratios different from 1:1.

Ionic Compound Examples

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A chemical compound must have a net charge of zero. If it contains ions, the charges of the ions must add up to zero in the formula for the compound. An ionic compound exists as a group of charged atoms. The chemical formula for an ionic compound represents the positive charge of the cation equals the negative charge of the anion. Consequently the overall charge is zero, and the ionic compound is neutral.

Give two examples of an ionic compound

Example of an ionic compound is given by considering the two common ionic compounds.
  1. Sodium chloride (NaCl)
  2. Magnesium oxide (MgO)
Some example of ionic compound are listed below.

S.No
Ionic compound
Formula
1 Sodium bromide NaBr
2
Potassium sulfide
K2S
3
Zinc sulfate
ZnSO4
4
Ammonium phosphate
(NH4)3PO4
5
Aluminum chromate
Al2(CrO4)3

Ionic and Molecular Compounds

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Compounds can be divided into two classes ionic or molecular compound. They are described in the following table. The chemical formulas of the compounds show the elements that compose them.

Ionic vs molecular compounds table is given below.

S.No
Ionic compounds
Molecular compounds
1
Compounds are formed by combination of reactive metals with reactive non metals. Compounds are formed by the combination of nonmetals with other non metals or with less reactive metals.
2
Crystalline solids. Solids, liquids and gases.
3
Hard and brittle. Solids are brittle and weak or soft and waxy.
4
High melting points. Low melting points.
5High boiling points.
Low boiling points.
6Good conductors of electricity when molten, poor conductors of electricity and heat when solid. Poor conductors of heat and electricity.
7Many are soluble in water. Many are insoluble in water but soluble in organic solvents.

Ionic and Covalent Compounds

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The ionic vs covalent compounds table is given below.

S.No
Ionic compounds
Covalent compounds
1 Crystalline solids (made of ions) Solids, liquids and gases (made of molecules)
2
High melting and boiling points. Low melting and boiling points.
3
Conduct electricity when melted. Poor electrical conductor in all phases.
4
Many soluble in water but net is non polar liquids. many soluble in non polar liquids but not soluble in water.

Binary Ionic Compound

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Binary Ionic Compound Definition

A binary compounds contains only two elements. In a binary ionic compound, both of the elements are present ions. The name of the compound consists of the name of the metal from which the cation was formed, by the name of anion.

Potassium and Sulfur Ionic Compound

Consider an ionic compound formed when potassium reacts with sulfur. Potassium is a Group 1A metal, so a potassium atom loses one electron to become a K+ ion. Sulfur is a Group 6A nonmetal, so a sulfur atom gains two electrons to become an S2- ion. To make the compound electrically neutral two K+ ions are needed for each S2- ion. Consequently the compound has the formula K2S.

Rules for Naming Ionic Compounds

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The following rules apply for naming ionic compounds.
  1. A simple cation has the same name as its parent element.
  2. The cation is always named first and the anion second.
  3. A simple cation takes its name from the name of the element. For example, Na+ is called sodium in the names of compounds containing this ion.
  4. A simple anion is named by taking the first part of the element name and adding -ide. Thus the Cl- ion is called chloride.
  5. In some cases the cation can assume more than one charge, the charge is specified by a Roman numeral in parentheses.

Ionic Compounds List

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Ionic compounds are composed of cations and anions. The attraction between these oppositely charged ions is called an ionic bond. The common ionic compound is given below as ionic compound table.

S.No
Ionic compound
Formula
1 Zinc oxide ZnO
2
Magnesium chloride
MgCl2
3
Copper sulfide
CuS
4
Potassium bromide
KBr
5
Calcium iodide
CaI2
6
Aluminum oxide
Al2O3

Ionic Compound Properties

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Properties of an Ionic Compound

The positive and negative ions formed during ionic bonding are held together by enormously strong forces of attraction between the oppositely charged ions. These ionic bonds between the charged particles result in a giant structure of ions.

Because the ions are held together tightly in these giant structures it takes a lot of energy to break all the bonds. As a result ionic compound melting point and boiling points are high.

Ionic Compound Characteristics

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There are many important characteristics of compounds having ionic bonds.
  1. An ionic compound is a collection of an equal number of positive and negative ions arranged in a three-dimensional lattice.
  2. Ionic compounds can be dissociated into their constituent ions with little effort.
  3. Further they can be electrolyzed to produce elements or covalent molecules of the constituent atoms.
  4. Water also weakens the attraction between the ions in an ionic compound.
  5. This is why ionic compounds dissolve well in water.
  6. Moreover ionic compounds can conduct electricity.
  7. Most ionic compounds are made of metals.


Is Water an Ionic Compound?

Water is a polar solvent and polar and ionic compounds tend to dissolve in water. So water is ionic solvent.


Is SO2 an Ionic Compound?

SO2 is not ionic but molecular compound, no electrons are actually transferred in the formation of this compound.


Is Salt an Ionic Compound?

Table salt is a familiar ionic compound formed from sodium and chlorine. Sodium forms an ion with a single positive charge Na+ and chlorine an ion with a single negative charge Cl-. The formula of salt is NaCl.


Is Sugar an Ionic Compound?

Sugar easily dissolve in water when we stir but its not an ionic compound. Sugar has many OH groups which forms hydrogen bonds to water and hence its very soluble in water.

Ionic Compound Nomenclature

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An ionic compound contains a metal and a nonmetal. Ionic compounds are also known as salts. An ionic compound is designated by giving the name of the cation first and then the name of the anion.

The nomenclature of ionic compounds involves three kinds of compounds
  1. Binary compounds (only two elements)
  2. Compounds of polyatomic ions (two or more elements that stay together and act as though they are one ion).
  3. Compounds of multivalent ions (contains more than one charge)

Ionic Compound Practice

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Example problems are given based on ionic compound.

Solved Examples

Question 1: Write the formula for these binary ionic compounds.
  1. Barium hydride
  2. Sodium fluoride
  3. Calcium oxide

Solution:
 
Write the formula of the positive ion and then the formula of the negative ion. Remember that the number of positive and negative charges must be equal. Show the ratio of each ion in the formula of the compound by subscripts. Where only one of either ion is present, do not show a subscript.
  1. BaH2
  2. NaF
  3. CaO

 

Question 2: Name these ionic compounds each of which contains a polyatomic ion.
  1. NaNO3
  2. CaCO3
  3. (NH4)2SO3
  4. NaH2PO4

Solution:
 
To name ionic compounds containing polyatomic ions, name the positive ion first and then the negative ion, each as a separate word.
  1. Sodium nitrate
  2. Calcium carbonate
  3. Ammonium sulfite
  4. Sodium dihydrogen phosphate