Direct comparison
Covalent vs ionic bond
A covalent bond shares pairs of electrons between atoms; an ionic bond transfers electrons to form oppositely charged ions that attract one another.
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Side-by-side comparison
| Dimension | Covalent bond | Ionic bond |
|---|---|---|
| What it is | A shared pair (or pairs) of electrons between two atoms. | An electrostatic attraction between oppositely charged ions. |
| What happens to electrons | Electrons are shared between the bonded atoms. | Electrons are transferred from one atom to another. |
| Atoms involved | Usually between two non-metals. | Usually between a metal and a non-metal. |
| Electronegativity difference | Small difference — electrons are pulled fairly evenly. | Large difference — one atom pulls electrons away entirely. |
| Particles formed | Discrete molecules (or covalent networks). | A lattice of cations and anions, not molecules. |
| Typical melting point | Often low for small molecules; very high for networks. | Generally high — the lattice is strongly held. |
| Electrical conductivity | Usually poor; molecules carry no free charge. | Conducts when molten or dissolved, as ions become free to move. |
| Example | Water (H₂O), methane (CH₄), oxygen (O₂). | Sodium chloride (NaCl), magnesium oxide (MgO). |
| State at room temperature | Often gases or liquids (small molecules) or hard solids (networks). | Hard, brittle, crystalline solids. |
It is a spectrum, not two sealed boxes
Most real bonds sit somewhere between purely covalent and purely ionic. The deciding factor is the difference in electronegativity — how strongly each atom pulls on shared electrons. When the difference is very small, electrons are shared evenly and the bond is non-polar covalent. A moderate difference gives a polar covalent bond, where electrons are shared but pulled toward the more electronegative atom. A large difference means electrons are effectively transferred, producing an ionic bond. So rather than asking simply "ionic or covalent?", chemists often ask how ionic or how covalent a given bond is.
Common questions
FAQ
How can I quickly tell if a bond is ionic or covalent?+
Look at the two atoms. A metal joined to a non-metal usually forms an ionic bond through electron transfer, while two non-metals usually form a covalent bond through electron sharing. A more precise guide is the electronegativity difference: a large difference points to ionic, a small one to covalent. Many bonds are intermediate (polar covalent), so this is a guide rather than a strict rule.
Why do ionic compounds conduct electricity but covalent ones often do not?+
Conductivity needs charged particles that are free to move. In an ionic compound the ions are locked in a solid lattice and cannot move, but once it melts or dissolves the ions become mobile and carry current. Most covalent compounds contain neutral molecules with no free charges, so they do not conduct — though some, like graphite, are exceptions.
Are ionic bonds stronger than covalent bonds?+
Not in a simple, universal way. Comparing a single covalent bond with the attraction between one pair of ions, the covalent bond is often stronger. But ionic compounds form vast lattices with countless attractions, which gives them high melting points overall. Strength depends on what you are comparing, so the blanket claim that one type is always stronger is misleading.
