Covalent bonds form when atoms share one or more pairs of electrons to achieve a more stable electron configuration. This sharing of electrons creates an attractive force that holds the atoms together.
Here's a more detailed explanation:
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Electron Sharing: Instead of transferring electrons (as in ionic bonds), atoms undergoing covalent bonding share electrons. This typically occurs between two nonmetal atoms.
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Electronegativity: The electronegativity difference between the atoms influences the type of covalent bond formed.
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Nonpolar Covalent Bond: When the electronegativity difference is small or zero, the electrons are shared equally. An example is the bond between two hydrogen atoms (H2).
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Polar Covalent Bond: When there's a significant electronegativity difference, the electrons are shared unequally. The atom with higher electronegativity attracts the electrons more strongly, resulting in a partial negative charge (δ-) on that atom and a partial positive charge (δ+) on the other atom. Water (H2O) is a prime example, where oxygen is more electronegative than hydrogen.
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Attraction to Nuclei: The shared electrons are attracted to the positively charged nuclei of both atoms participating in the bond. This attraction is the fundamental force holding the atoms together in the covalent bond. The shared electrons spend most of their time between the two nuclei, effectively shielding the positive charges and minimizing repulsion.
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Stability: Atoms form covalent bonds to achieve a stable electron configuration, typically resembling that of a noble gas (octet rule, with some exceptions). By sharing electrons, atoms can fill their outermost electron shells and minimize their overall energy.
Examples:
| Molecule | Bond Type | Explanation |
|---|---|---|
| H2 | Nonpolar Covalent | Hydrogen atoms have equal electronegativity, leading to equal sharing of electrons. |
| H2O | Polar Covalent | Oxygen is more electronegative than hydrogen, resulting in unequal sharing of electrons and partial charges (δ+ on H, δ- on O). |
| CH4 | Polar Covalent | Carbon is slightly more electronegative than hydrogen, resulting in unequal sharing of electrons and partial charges (δ+ on H, δ- on C), though the molecule as a whole is nonpolar due to its geometry. |
In summary, covalent bonds are formed through the sharing of electrons between atoms, driven by the atoms' need to achieve stability and the attraction of the shared electrons to the positively charged nuclei. The electronegativity difference determines whether the bond is polar or nonpolar.
