What are the differences between ionic and covalent bonds?

Definition

Ionic bonds are chemical bonds formed through the transfer of electrons from one atom (typically a metal) to another (typically a nonmetal), resulting in oppositely charged ions that attract each other.

Covalent bonds are chemical bonds formed when two atoms (usually nonmetals) share one or more pairs of electrons.

Worked Example

Ionic Bond Example: Sodium Chloride ($\mathrm{NaCl}$)

• Sodium ($\mathrm{Na}$) loses one electron to become $\mathrm{Na}^+$.
• Chlorine ($\mathrm{Cl}$) gains one electron to become $\mathrm{Cl}^-$.
• The electrostatic attraction between $\mathrm{Na}^+$ and $\mathrm{Cl}^-$ forms the ionic bond.

$$ \mathrm{Na} \rightarrow \mathrm{Na}^+ + e^- $$

$$ \mathrm{Cl} + e^- \rightarrow \mathrm{Cl}^- $$

$$ \mathrm{Na}^+ + \mathrm{Cl}^- \rightarrow \mathrm{NaCl} $$

Covalent Bond Example: Water ($\mathrm{H_2O}$)

• Each hydrogen atom shares one electron with oxygen.
• Oxygen shares two electrons (one with each hydrogen), forming two covalent bonds.

$$ \mathrm{H} \cdot + \cdot \mathrm{O} \cdot \cdot + \cdot \mathrm{H} \rightarrow \mathrm{H} - \mathrm{O} - \mathrm{H} $$

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Key Takeaways

• Ionic bonds involve electron transfer and form between metals and nonmetals; covalent bonds involve electron sharing and form between nonmetals.
• Ionic compounds form crystalline solids with high melting points; covalent compounds can be gases, liquids, or solids with generally lower melting points.
• Ionic compounds conduct electricity when dissolved in water; covalent compounds usually do not.