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 DefinitionBack to Top
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 FormulaBack to Top
The following guidelines ensure uniformity in writing formulas for ionic compounds. The formula unit of an ionic compound shows the
- The cation is always listed before the anion.
- The formula of any polyatomic ion is written as a unit.
- Polyatomic ions are placed in parentheses with subscripts to indicate ratios different from 1:1.
Ionic Compound ExamplesBack to Top
Give two examples of an ionic compound
Example of an ionic compound is given by considering the two common ionic compounds.
- Sodium chloride (NaCl)
- Magnesium oxide (MgO)
Ionic and Molecular CompoundsBack to Top
Ionic vs molecular compounds table is given below.
||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.
||Crystalline solids.||Solids, liquids and gases.
||Hard and brittle.||Solids are brittle and weak or soft and waxy.|
||High melting points.||Low melting points.
|5||High boiling points. ||Low boiling points.|
|6||Good conductors of electricity when molten, poor conductors of electricity and heat when solid.||Poor conductors of heat and electricity.|
|7||Many are soluble in water.||Many are insoluble in water but soluble in organic solvents.|
Ionic and Covalent CompoundsBack to Top
|1||Crystalline solids (made of ions)||Solids, liquids and gases (made of molecules)
||High melting and boiling points.||Low melting and boiling points.
||Conduct electricity when melted.||Poor electrical conductor in all phases.|
||Many soluble in water but net is non polar liquids.||many soluble in non polar liquids but not soluble in water.|
Binary Ionic CompoundBack to Top
Potassium and Sulfur Ionic Compound
Rules for Naming Ionic CompoundsBack to Top
- A simple cation has the same name as its parent element.
- The cation is always named first and the anion second.
- 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.
- A simple anion is named by taking the first part of the element name and adding -ide. Thus the Cl- ion is called chloride.
- In some cases the cation can assume more than one charge, the charge is specified by a Roman numeral in parentheses.
Ionic Compounds ListBack to Top
Ionic Compound PropertiesBack to Top
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 CharacteristicsBack to Top
- An ionic compound is a collection of an equal number of positive and negative ions arranged in a three-dimensional lattice.
- Ionic compounds can be dissociated into their constituent ions with little effort.
- Further they can be electrolyzed to produce elements or covalent molecules of the constituent atoms.
- Water also weakens the attraction between the ions in an ionic compound.
- This is why ionic compounds dissolve well in water.
- Moreover ionic compounds can conduct electricity.
- 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 NomenclatureBack to Top
The nomenclature of ionic compounds involves three kinds of compounds
- Binary compounds (only two elements)
- Compounds of polyatomic ions (two or more elements that stay together and act as though they are one ion).
- Compounds of multivalent ions (contains more than one charge)
Ionic Compound PracticeBack to Top
- Barium hydride
- Sodium fluoride
- Calcium oxide
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.
To name ionic compounds containing polyatomic ions, name the positive ion first and then the negative ion, each as a separate word.
- Sodium nitrate
- Calcium carbonate
- Ammonium sulfite
- Sodium dihydrogen phosphate