The correct option is **C. Covalent bond**. ### Explanation of the Correct Answer A **covalent bond** is formed when two atoms share one or more pairs of electrons. This type of bond typically occurs between nonmetal atoms, which have similar electronegativities. By sharing electrons, each atom can achieve a more stable electron configuration, often resembling that of the nearest noble gas. #### Step-by-Step Breakdown: 1. **Electron Sharing**: In a covalent bond, atoms share electrons to fill their outer electron shells. For example, in a water molecule (H₂O), each hydrogen atom shares one electron with the oxygen atom, allowing all three atoms to achieve a full outer shell. 2. **Molecular Formation**: The sharing of electrons leads to the formation of molecules. For instance, two hydrogen atoms (H) can bond with one oxygen atom (O) to form a water molecule (H₂O). This is a classic example of covalent bonding. 3. **Bond Strength and Length**: Covalent bonds can vary in strength and length depending on the number of shared electron pairs. A single bond involves one pair of shared electrons, a double bond involves two pairs, and a triple bond involves three pairs. Generally, as the number of shared electron pairs increases, the bond becomes stronger and shorter. 4. **Polarity**: Covalent bonds can be polar or nonpolar. If the atoms sharing electrons have different electronegativities, the shared electrons may spend more time closer to one atom than the other, creating a dipole moment. For example, in a water molecule, the oxygen atom is more electronegative than the hydrogen atoms, resulting in a polar covalent bond. ### Explanation of Incorrect Options - **A. Ionic bond**: An ionic bond is formed when one atom donates an electron to another atom, resulting in the formation of charged ions. These oppositely charged ions attract each other. For example, in sodium chloride (NaCl), sodium (Na) loses an electron to become Na⁺, while chlorine (Cl) gains an electron to become Cl⁻. This is fundamentally different from the sharing of electrons in covalent bonds. - **B. Metallic bond**: Metallic bonds occur between metal atoms, where electrons are not shared or transferred but are instead delocalized over a lattice of metal cations. This "sea of electrons" allows metals to conduct electricity and heat and gives them their malleability and ductility. This is distinct from covalent bonding, where electrons are shared between specific atoms. - **D. Hydrogen bond**: A hydrogen bond is a type of weak attraction that occurs between a hydrogen atom covalently bonded to a highly electronegative atom (like oxygen or nitrogen) and another electronegative atom. While hydrogen bonds are important in biological systems (like in water and DNA), they are not a type of bond formed by the sharing of electrons between atoms. Instead, they are intermolecular forces that arise from polar covalent bonds. ### Summary of Key Points - **Covalent bonds** involve the sharing of electrons between atoms, leading to the formation of molecules. - They can be **polar** or **nonpolar** depending on the electronegativity of the atoms involved. - **Ionic bonds** involve the transfer of electrons, while **metallic bonds** involve delocalized electrons in a lattice. - **Hydrogen bonds** are weak attractions between molecules, not a type of covalent bond. This understanding of covalent bonds is crucial for grasping more complex concepts in chemistry, such as molecular geometry, reactivity, and the properties of substances.