Water is categorized as a polar covalent molecule because it consists of two different elements, oxygen (O) and hydrogen (H), which share electrons unevenly in covalent bonds. Here's an explanation of its structure and the type of bond it forms:
1. **Structure of an Individual Water Molecule:** A water molecule (H2O) consists of two hydrogen atoms and one oxygen atom. The oxygen atom is at the center, forming a V-shaped molecule. Each hydrogen atom shares one of its electrons with the oxygen atom, resulting in two single covalent bonds (H-O-H). The oxygen atom is more electronegative than hydrogen, meaning it has a greater attraction for electrons. As a result, the electrons are pulled closer to the oxygen atom.
2. **Type of Bond Formed:** The bonds between the hydrogen atoms and the oxygen atom in a water molecule are covalent bonds. Specifically, they are polar covalent bonds. In a polar covalent bond, electrons are shared between atoms, but due to differences in electronegativity, one atom (in this case, oxygen) has a partial negative charge (δ-) because it attracts electrons more, while the other atom (hydrogen) has a partial positive charge (δ+). This unequal sharing of electrons creates a polarity within the molecule, where one end (the oxygen end) is slightly negative, and the other end (the hydrogen end) is slightly positive.
This polarity in water molecules results in some unique properties of water, such as its ability to form hydrogen bonds with other water molecules, which gives it a high surface tension, high heat capacity, and the ability to dissolve a wide range of substances. It's also the reason why water exhibits a strong cohesive and adhesive nature and why it has a relatively high boiling and melting point for its molecular size.