The water molecule, chemically known as H₂O, stands as a fundamental substance on Earth, playing a central role in all known forms of life. Composed of oxygen and hydrogen atoms, it is abundant, covering about 75% of the Earth’s surface and over 60% of the human body. Understanding its atomic arrangement and the forces within and between its molecules is foundational to grasping many natural phenomena.
Atomic Composition and Covalent Bonds
A single water molecule is formed from one oxygen atom and two hydrogen atoms. These atoms are held together by covalent bonds. In a covalent bond, atoms share electrons to achieve stability. The lines connecting the oxygen and hydrogen atoms in a water molecule diagram represent these shared electron pairs.
The sharing of electrons in water’s covalent bonds is not equal. The oxygen atom has a stronger pull on the shared electrons compared to the hydrogen atoms, a property known as electronegativity. Consequently, electrons spend more time closer to the oxygen atom, making the oxygen end of the molecule slightly more negative and the hydrogen ends slightly more positive. This unequal distribution leads to the molecule’s unique characteristics.
Molecular Geometry and Polarity
The water molecule exhibits a bent, or “V” shape, rather than a linear arrangement. This geometry arises because the oxygen atom possesses two pairs of electrons not involved in bonding with hydrogen atoms, known as lone pairs. These lone pairs and the two bonding pairs of electrons repel each other, pushing the hydrogen atoms closer. This repulsion leads to an approximate tetrahedral arrangement of electron clouds around the oxygen, resulting in an H-O-H bond angle of about 105 degrees.
This asymmetrical bent shape and uneven electron sharing cause the water molecule to be polar. The oxygen atom acquires a partial negative charge (often denoted as δ-), while each hydrogen atom develops a partial positive charge (δ+). These distinct positive and negative regions create a molecular dipole, making water a “polar molecule.”
Hydrogen Bonding Between Molecules
The polarity of water molecules enables them to attract one another. The partially positive hydrogen of one water molecule is drawn to the partially negative oxygen of a neighboring water molecule. This attractive force is termed a hydrogen bond.
Hydrogen bonds are weaker than the covalent bonds within a water molecule, but their collective strength significantly influences water’s properties. These intermolecular attractions are responsible for phenomena such as water’s high surface tension, allowing some insects to walk on water, and its cohesive nature, causing water molecules to stick together.