In a covalent bond, atoms share electrons to achieve a stable electron configuration. Covalent bonding typically occurs between two non-metal atoms that have similar electronegativity values. These atoms have a relatively equal attraction for electrons, and as a result, they share electrons in order to complete their valence shells and achieve a more stable electron configuration.
For example, consider the formation of a covalent bond between two hydrogen (H) atoms. Each hydrogen atom has one electron in its valence shell and requires one more electron to achieve a stable configuration. By sharing their electrons, both hydrogen atoms can achieve a complete valence shell with two electrons, similar to the configuration of helium (He). The shared electrons create a covalent bond between the two hydrogen atoms.
In contrast, an ionic bond forms between a metal atom and a non-metal atom or between atoms with a large electronegativity difference. In this type of bond, one atom has a significantly higher electronegativity than the other, resulting in a strong attraction for electrons. The atom with higher electronegativity tends to "steal" or gain electrons from the other atom, leading to the formation of ions with opposite charges.
For example, consider the formation of an ionic bond between sodium (Na) and chlorine (Cl). Sodium has a relatively low electronegativity, while chlorine has a high electronegativity. Sodium has one electron in its valence shell, while chlorine requires one more electron to achieve a stable configuration. To fulfill this requirement, sodium tends to lose its single valence electron, becoming a positively charged sodium ion (Na+). Chlorine, on the other hand, tends to gain the electron from sodium, resulting in a negatively charged chloride ion (Cl-). The electrostatic attraction between the oppositely charged ions forms the ionic bond.
In summary, the difference lies in the relative electronegativity of the atoms involved. In covalent bonding, atoms with similar electronegativity share electrons, whereas in ionic bonding, atoms with a significant electronegativity difference lead to the transfer of electrons, resulting in the formation of ions with opposite charges.