TeXes Science Practice Test

What is the main purpose of covalent bonds in a water molecule?

1. To transfer electrons

2. To share electrons

3. To attract oppositely charged ions

4. To form a crystal lattice

The correct answer is: To share electrons

The main purpose of covalent bonds in a water molecule is to share electrons. In a water molecule, each hydrogen atom shares one of its electrons with the oxygen atom, resulting in a covalent bond. This sharing allows the atoms to achieve greater stability by filling their outer electron shells; oxygen, which has six valence electrons, needs two more to complete its octet, and each hydrogen, with its single valence electron, can achieve the same by sharing. The unique properties of water, such as its high specific heat, surface tension, and solvent capabilities, stem from the polar nature of these covalent bonds. The unequal sharing of electrons—the oxygen atom is more electronegative than hydrogen—results in a slight negative charge on the oxygen and a slight positive charge on the hydrogen atoms, contributing to water's polarity and the formation of hydrogen bonds between water molecules. In contrast, transferring electrons is characteristic of ionic bonds, while attracting oppositely charged ions pertains to ionic interactions rather than covalent ones. Forming a crystal lattice is typically associated with the structure of ionic compounds and does not apply to the molecular structure of water. Thus, the sharing of electrons is fundamental to the formation and properties of water molecules.