Ionic bonds form when atoms transfer electrons, resulting in positively and negatively charged ions that attract each other. Covalent bonds, on the other hand, involve the sharing of electrons between atoms. 

While ionic compounds often form crystalline solids and conduct electricity in solution, covalent compounds can exist as gases, liquids, or solids and typically do not conduct electricity.

Ionic vs. Covalent Bond

Ionic Bond Covalent Bond
An ionic bond is formed due to the electrostatic attraction between oppositely charged ions. A covalent bond is formed by the mutual sharing of electron pairs between atoms.
In ionic bonds, electrons are transferred from one atom (usually a metal) to another (usually a non-metal). In covalent bonds, electrons are shared between atoms, either equally or unequally.
Ionic bonds are formed when one atom loses electrons to become a cation, and another atom gains those electrons to become an anion. Covalent bonds are formed when two atoms come together and share electrons to achieve stability.
In ionic bonds, the electronegativity difference between atoms is usually greater than 1.7. In covalent bonds, the electronegativity difference is typically less than 1.7. A near-zero difference indicates a non-polar bond.
Ionic bonds are generally stronger in their crystalline forms due to the lattice structure of ions, but these bonds can be disrupted when dissolved in aqueous solutions. The strength of covalent bonds can vary, ranging from weaker single bonds to very strong triple bonds, based on the number of shared electron pairs.
Most ionic compounds, such as salts, are solid at room temperature. Covalent compounds can exist as solids, liquids, or gases at room temperature, depending on their molecular structure and size.
Ionic compounds are typically soluble in water, as they can dissociate into their constituent ions. The solubility of covalent compounds in water varies; polar molecules tend to be soluble, while non-polar molecules are often insoluble.
Ionic compounds are good conductors of electricity when in molten form or in aqueous solution because of the movement of free ions. Covalent compounds are typically poor conductors of electricity in all states because they do not have free-moving charged particles.
Examples of ionic bonds include Sodium chloride (NaCl) and Magnesium oxide (MgO). Examples of covalent bonds include Water (H₂O), Methane (CH₄), and Carbon dioxide (CO₂).

What is an Ionic Bond?

An ionic bond is a type of chemical bond that arises from the electrostatic attraction between positively and negatively charged ions. This bond forms when atoms lose or gain electrons, resulting in the formation of cations (positively charged ions) and anions (negatively charged ions). Typically, ionic bonding occurs between metals, which tend to lose electrons, and non-metals, which tend to gain electrons.

Formation of Ionic Bonds with Examples

Sodium Chloride (NaCl)

Sodium (Na) has one electron in its outermost shell. To achieve a stable electron configuration similar to noble gases, it loses this electron.

Chlorine (Cl), on the other hand, has seven electrons in its outermost shell and needs one more to achieve stability.

Thus, sodium donates its electron to chlorine, resulting in the formation of sodium ion Na+ and chloride ion Cl

The attraction between these two oppositely charged ions forms an ionic bond, producing sodium chloride.

Magnesium Oxide (MgO)

  • Magnesium (Mg) has two electrons in its outermost shell. It loses these electrons to achieve a noble gas electron configuration.
  • Oxygen (O) has six electrons in its outermost shell and requires two more for stability.
  • Magnesium donates its two electrons to oxygen, leading to the formation of magnesium ion Mg2+ and oxide ion O2−
  • The electrostatic attraction between them results in an ionic bond, producing magnesium oxide.

Common Ionic Compounds

Sodium Chloride (NaCl) – Commonly known as table salt, it’s used in cooking and food preservation.

Potassium Bromide (KBr) – Used in photographic films and medicinal preparations.

Calcium Carbonate (CaCO3) – Found in antacids, chalk, limestone, and shells of marine organisms.

Magnesium Sulfate (MgSO4) – Known as Epsom salts, used in bath salts and as a drying agent in organic synthesis.

Factors Affecting the Strength of Ionic Bonds

Charge of the Ions: Ions with higher charges tend to form stronger ionic bonds.

Size of the Ions: Smaller ions tend to form stronger ionic bonds because they can get closer to each other, leading to a stronger electrostatic attraction. For example, LiF has a stronger ionic bond than NaF because lithium and fluoride ions are smaller than sodium and fluoride ions.

Lattice Energy: This is the energy required to separate one mole of an ionic compound into its individual ions. Higher lattice energy indicates stronger ionic bonding. The magnitude of lattice energy is influenced by the charge and size of the ions.

Dielectric Constant of the Solvent: The strength of the ionic bond can also be influenced by the medium in which the ions are present. A solvent with a high dielectric constant can weaken the strength of the ionic bond by reducing the force of attraction between the ions.

What is a Covalent Bond?

A covalent bond is a type of chemical bond formed when two atoms share one or more pairs of electrons. This sharing allows each atom to achieve a stable electron configuration, similar to that of noble gases. Covalent bonds typically form between non-metals.

Formation of Covalent Bonds with Examples

Hydrogen Molecule (H2)

Each hydrogen (H) atom has one electron in its outer shell and needs one more to achieve the stable configuration of helium.

By sharing their single electrons, the two hydrogen atoms form a covalent bond, resulting in a hydrogen molecule.

Water (H2O)

Oxygen (O) has six electrons in its outermost shell and needs two more for a full shell.

Two hydrogen atoms each share their single electron with oxygen, forming two covalent bonds and resulting in a water molecule.

Common Covalent Compounds

  • Methane (CH4) – The primary component of natural gas, it’s used as a fuel and in organic synthesis.
  • Carbon Dioxide (CO2) – Produced during respiration and combustion, it’s also a greenhouse gas in the atmosphere.
  • Ammonia (NH3) – Used in fertilizers and as a refrigerant.
  • Ethanol (C2H5OH) – Commonly known as alcohol, it’s found in alcoholic beverages and used as a solvent.

Factors Affecting the Strength of Covalent Bonds

Electronegativity Difference: The strength of a covalent bond can be influenced by the difference in electronegativity between the two bonded atoms. A greater difference might result in a polar covalent bond, while a smaller difference usually results in a non-polar covalent bond.

Bond Length: The distance between the two bonded nuclei affects bond strength. Shorter bonds (like the bond in H2) are generally stronger than longer ones.

Bond Multiplicity: A single bond (like the one in CH4) is weaker than a double bond (like the one in O2) or a triple bond (like the one in N2). The more electron pairs shared between two atoms, the stronger the bond.

Resonance: Some molecules, like benzene (C6H6), have resonance structures. This delocalization of electrons can stabilize the molecule and affect bond strength.

Overlap of Orbitals: The extent and type of orbital overlap can affect bond strength. For instance, a sigma (σ) bond formed by the direct overlap of atomic orbitals is stronger than a pi (π) bond formed by the sideways overlap of p orbitals.

Polarity of Bonds

The polarity of a bond pertains to the distribution of electrical charge around the atoms involved in the bond. When two atoms share a covalent bond, the electron pair is not always shared equally. This imbalance is due to differences in the electronegativity of the bonded atoms. Electronegativity is a measure of an atom’s ability to attract and hold onto electrons.

Non-Polar Covalent Bonds

When two atoms with identical or very similar electronegativities (typically a difference of 0.4 or less) bond together, the electron pair is shared equally between them.

Since both atoms pull on the electron pair with the same strength, no charge separation occurs. The bond is thus termed non-polar.

Examples include the bonds in O2, N2, and the C-H bonds in methane (CH4).

Polar Covalent Bonds

When two atoms with differing electronegativities form a bond, the electron pair isn’t shared equally. The atom with the higher electronegativity will pull the shared electrons closer to itself.

This results in a partial negative charge (δ) on the more electronegative atom and a partial positive charge (δ+) on the other atom. This charge separation makes the bond polar.

Examples include the bonds in water (H2O) where oxygen is more electronegative than hydrogen, leading to a polar bond.

Ionic Bonds and Polarity

Technically, ionic bonds are the extreme cases of polarity, where the electron transfer is complete from one atom to another. This results in the formation of cations (positively charged ions) and anions (negatively charged ions).

Ionic compounds inherently exhibit polarity due to the presence of oppositely charged ions. However, while ionic compounds are polar, it’s not accurate to describe the ionic bond itself as “polar” because there’s a complete transfer of electrons rather than a sharing.

Molecular Polarity

While individual bonds can be polar, the molecule as a whole might not be. The molecular polarity depends on both the polarity of individual bonds and the shape of the molecule. For example, carbon tetrachloride (CCl4) has polar C-Cl bonds, but the symmetrical tetrahedral shape of the molecule ensures that the polarities cancel out, making the entire molecule non-polar.

The Physical Properties of Ionic and Covalent Compounds

Ionic Compounds:

High Melting and Boiling Points: Due to the strong electrostatic forces between ions.

Solid State: Usually form crystalline solids at room temperature.

Conductivity: Conduct electricity when molten or dissolved in water because of the movement of ions.

Solubility: Often soluble in water due to the interaction between ions and water molecules.

Covalent Compounds:

Lower Melting and Boiling Points: Compared to ionic compounds, because the forces between molecules (Van der Waals forces) are generally weaker than ionic bonds.

State: Can be gases, liquids, or solids at room temperature.

Conductivity: Typically poor conductors of electricity as they don’t have free ions or delocalized electrons.

Solubility: Varies widely; some are water-soluble while others are not.

The Chemical Properties of Ionic and Covalent Compounds

Ionic Compounds:

Reactivity: Often reactive with opposite ions. For example, a positive ion (cation) of one compound will react with the negative ion (anion) of another.

Formation of Aqueous Solutions: When dissolved in water, they dissociate into their respective ions.

Electrolysis: Can be decomposed by passing electricity through their molten state or aqueous solutions.

Covalent Compounds:

Reactivity: Reactivity varies widely and depends more on specific atoms within the molecule than on bond type.

Non-Electrolytes: Generally, they do not produce ions when dissolved in water, so they do not conduct electricity.

Combustion: Organic covalent compounds, especially hydrocarbons, undergo combustion in the presence of oxygen to produce carbon dioxide and water.

The Applications of Ionic and Covalent Compounds

Ionic Compounds:

Industrial: Used in the making of ceramics, metals, and other materials.

Agricultural: Many fertilizers are ionic compounds, such as ammonium nitrate.

Medicinal: Some medicines are ionic, like lithium carbonate, which is used to treat bipolar disorder.

Food: Table salt (sodium chloride) is a crucial ionic compound in culinary uses.

Covalent Compounds:

Pharmaceuticals: Many drugs are covalent compounds, like aspirin (acetylsalicylic acid).

Fuels: Hydrocarbons, like methane, propane, and octane, are covalent and used as fuels.

Plastics and Polymers: Most plastics are based on covalent compounds.

Detergents and Soaps: These often contain covalent compounds that help in cleaning processes.

Overviewing the Key Differences Between Ionic and Covalent Bonds

Ionic vs covalent bond