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How do covalent bonds differ from metallic bonds?

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Diagram showing the formation of a polar covalent bond in a water molecule, with two hydrogen atoms bonding to one oxygen atom to form H2O, illustrating shared electrons and chemical reaction. — covalent bond In polar covalent bonds, such as that between hydrogen and oxygen atoms, the electrons are not transferred from one atom to the other as they are in an ionic bond. Instead, some outer electrons merely spend more time in the vicinity of the other atom. The effect of this orbital distortion is to induce regional net charges that hold the atoms together, such as in water molecules.

Covalent and metallic bonds differ primarily in how valence electrons are distributed between atoms.

A covalent bond is formed when atoms share pairs of electrons to achieve stability. These bonds are typically directional, involving the interaction of specific atomic orbitals (such as sigma and pi bonds) between nonmetal atoms.12

In contrast, a metallic bond is characterized by nonlocalized valence electrons. In metals, these electrons are not associated with any specific pair of atoms; instead, they are free to wander throughout the entire crystal lattice. This "sea" of mobile electrons acts as a buffer between positive metal ions, which accounts for properties like high electrical conductivity, malleability, and ductility.345

While most metallic bonding involves these free-roaming electrons, some transition metals also utilize covalent-like bonding through their partially filled d-orbitals, which are more tightly bound to the ion and provide greater mechanical strength than the weak bonds found in simple metals.4