Ionic vs Covalent Bonding
Ionic bonding
Ionic bonding is the electrostatic attraction between oppositely charged ions that forms when one atom transfers one or more electrons to another. Typically a metal loses electrons to become a positive ion (cation) while a nonmetal gains electrons to become a negative ion (anion), and the ions pack into a repeating three-dimensional crystal lattice.
Example: Table salt, NaCl: a sodium atom donates one electron to a chlorine atom, forming Na+ and Cl- ions that lock together in a crystal lattice.
Covalent bonding
Covalent bonding is the sharing of one or more pairs of electrons between two atoms, usually nonmetals. Neither atom fully gives up or takes electrons; instead, both nuclei attract the same shared electron pair, which holds the atoms together in discrete molecules or extended networks.
Example: Hydrogen gas, H2: two hydrogen atoms share a single electron pair, each effectively gaining the stable two-electron configuration of helium.
Key differences
| Aspect | Ionic bonding | Covalent bonding |
|---|---|---|
| How electrons are handled | Electrons are transferred from one atom to another, creating charged ions. | Electrons are shared between atoms; no ions are formed. |
| Typical structure | A repeating 3D crystal lattice of alternating positive and negative ions, with no individual molecules. | Discrete molecules with a fixed number of atoms (exceptions like diamond form networks instead). |
| Melting and boiling points | Generally high, because the strong lattice of electrostatic attractions must be broken (NaCl melts at 801 °C). | Generally lower, because only weak forces between separate molecules need breaking (water melts at 0 °C). |
| Electrical conductivity | Conducts when molten or dissolved in water, because the ions become free to move; solid ionic compounds do not conduct. | Usually does not conduct in any state, because there are no mobile charged particles (graphite is a notable exception). |
| State and appearance | Almost always hard, brittle crystalline solids at room temperature. | Can be gases, liquids, or soft solids at room temperature (oxygen gas, liquid water, solid sugar). |
Both bond types let atoms reach a stable electron arrangement, and some bonds are in-between (polar covalent bonds have unequal sharing, like in water). A good rule of thumb: metal + nonmetal usually gives an ionic compound, while two nonmetals usually give a covalent one. Also note that network covalent solids like diamond or quartz break the 'low melting point' rule — they melt at thousands of degrees because the whole crystal is one giant molecule.