State the characteristic properties of ionic compounds.

• Ionic compounds are mostly crystalline solids. 
• Ionic compounds in solid state have slightly electrical conductance but they are good conductors in solution and in the molten form. It is due to presence of free ions in them.  
• Ionic compounds have high melting and boiling points. 
• They dissolve easily in polar solvents like water.   

Properties of Ionic or Electrovalent Compound

Example of ionic or electrovalent compound

• Solid at room temperature
• High melting/ boiling point
• Soluble in water
• Molten ionic compounds conduct electricity because they contain mobile ions (cations & anions)

State three differences between an ionic compound and a covalent compound

Three differences between an ionic compound and covalent compound are:

•  An ionic compound has high boiling and melting point whereas covalent compound has low melting and boiling point. 
• An ionic compound is soluble in water but is insoluble in organic solvents, whereas a covalent compounds is soluble in organic solvent but is insouble in water.
• An ionic compounds conducts electricity in the liquid state and in aqueous solution whereas a covalent compounds does not conduct electricity in any state. 

Why ionic compounds have high boiling point than covalent compounds?

• Ionic compounds consist entirely of ions. The opposite charged ions are held close to one another by very strong electrostatic attraction, known as ionic bonds. Hence large amount of energy needed to break ionic bonds. Therefore high boiling points.  
• Covalent compounds consist entirely of molecules as they are formed by sharing of electrons. Forces between molecules are very weak. Only small amount of energy needed to break binds.  Therefore low boiling points. 

Properties of ionic compounds

• Ionic compounds are hard crystalline solids with flat sides and regular shapes because the ions are arranged in straight rows in strong ionic bonds.
• Ionic compounds have very high melting points and boiling points.
• The strong forces holding ionic compounds prevent them to evaporate easily. Hence, ionic compounds have no smell.
• Solid ionic compounds don’t conduct electricity but they do when they are aqueous or molten. This is because in liquid/aqueous state the ions which conduct electricity are free to move. In solids, these ions are fixed in place.
• Ionic compounds are soluble in water but insoluble in organic compounds. This is because the ions attract water molecules which disrupt the crystal structure, causing them separate & go into solution. Vice versa is when in organic solvent.

Formation of magnesium floride

Magnesium atom loses two electrons by transferring the electrons to fluorine atoms, one each, making both stable. The loss of electron forms cation, Mg²⁺, as it loses 2 electrons, and the gain of electron forms anion, F^-. The opposite charges acquired by both ions attract to each other, forming a strong ionic bond of MgF₂.

Formation of NaCl

Sodium atom loses an electron by transferring the electron to chlorine atom, making both stable. The loss of electron forms cation, Na⁺, and the gain of electron forms anion, Cl^-. The opposite charges acquired by both ions attract to each other, forming a strong ionic bond of NaCl.

Ionic compounds

An ionic compound is a compound formed by ions bonding together through electrostatic forces. Ionic compounds form when positive and negative ions share electrons and form an ionic bond. The strong attraction between positive and negative ions often produces crystalline solids that have high melting points. Ionic bonds form instead of covalent bonds when there is a large difference in electronegativity between the ions.

An ionic bond is formed when one atom accepts or donates one or more of its valence electrons to another atom. 

Example: ionic bond between the sodium and chloride ions in table salt, NaCl.

• Ionic compounds have high melting and boiling points.
• Ionic compounds are mostly soluble in water but insoluble in organic solvents.
• Ionic compounds can conduct electricity in molten state but cannot conduct electricity in solid state. 

SPM Form 4: Chemical Bonds (Checklist)

• An ionic bond is a chemical link between two atoms caused by the electrostatic force between oppositely-charged ions in an ionic compound. Examples: an ionic bond between the sodium and chloride ions in table salt, NaCl.

• A covalent bond is a chemical link between two atoms in which electrons are shared between them. Examples: a covalent bond between the oxygen and hydrogen in a water molecule (H₂O).

• Ionic compounds: a compound that consists of positive ions and negative ions arranged in the crystal lattice and are attracted to each other by strong electrostatic forces. Ionic compounds such as magnesium oxide, MgO, sodium chloride, NaCl and iron(III) chloride, FeCl₃ can be respectively prepared through a reaction between a metal and a non-metal.
• Covalent compounds are those in which the elements share electrons via covalent bonds.
• Ionic compounds have high melting and boiling point whereas covalent compounds have low melting and boiling points.
• Ionic compounds are mostly soluble in water but insoluble in organic solvents. Covalent compounds are mostly insoluble in water but soluble in organic solvents.
• Ionic compounds can conduct electricity in molten state but cannot conduct electricity in solid state. Covalent compounds cannot conduct electricity in solid and molten states.
• Melting points: the temperature at which a solid turns into a liquid at a fixed pressure.
• Boiling point: the temperature at which the vapor pressure of a liquid equals the external pressure surrounding the liquid.
• Solubility: the maximum quantity of a substance that may be dissolved in another or the maximum amount of solute that may be dissolved in a solvent.