Ionic, covalent, and metallic bonds are different types of chemical bonds. An ionic bond is formed when one atom donates valence electrons to another atom. A covalent bond is formed when both atoms share pairs of valence electrons. A metallic bond is formed between a cloud of free electrons and the positively charged ions in a metal.

In ionic and covalent bonds, the valence electrons play a critical role in forming the bond. Atoms achieve a stable electronic configuration by transferring and sharing electrons. As a result, the bonds become stable with well-defined strength and energy.

Ionic Bond vs. Covalent Bond vs. Metallic Bond
	Ionic Bond	Covalent Bond	Metallic Bond
Occurs between	A metal and a nonmetal	Two nonmetals or a nonmetal and a metalloid	Positively charged ions and negatively charged electron cloud
Formation	Electrostatic attraction between oppositely charged ions	Sharing pairs of electrons	Electrostatic attraction between the delocalized electron cloud and positively charged metal ions
Formation between atoms of the same element	No	Yes	–
Electronegativity difference between atoms	High (>2)	Low (<0.1) for nonpolar compounds and intermediate (0.1 – 2) for polar compounds	Electronegativity does not play any role
Isomerism	Nondirectional	Directional	Nondirectional
Physical state of compounds	Solid at room temperature	Liquid or gas at room temperature	Solid at room temperature
Physical properties	High melting and boiling points	Low melting and boiling points	High melting and boiling points
Solubility	Dissociate into ions in solution	Retain their molecular identity in solution	Some metals react vigorously with water, while others do not
Conductivity	Low in solid-state, but becomes high in molted state and solutions	Low, except conducting polymers	High
Examples	Sodium chloride (NaCl) and potassium iodide (KI)	Methane (CH4) and water (H2O)	Sodium (Na) and potassium (K)

Similarities between Ionic and Covalent Bonds

• Valence electrons participate in bonding
• Form neutral, stable compounds
• Compounds are formed through exothermic reactions
• Compounds have faster rates of reactivity
• Ionic compounds are always polar. Some covalent compounds are also polar.
• Ionic compounds are crystalline. Some covalent compounds are also crystalline.

Similarities between Ionic and Metallic Bonds

• Involve electrostatic attractions
• Metallic bond has high thermal and electrical conductivities. The ionic bond can have high conductivities in molten states and solutions.
• Ionic compounds and metals have high melting and boiling points.
• Ionic compounds and metals are solid at room temperature

Similarities between Covalent and Metallic Bonds

• Metals are solid at room temperature. Some covalent compounds are solid at room temperature.