Properties of Water, Structure of Water and Ice - JEE PDF Download

Physical Properties of Water

Water, the universal liquid that permeates 99% of life's functions, possesses remarkable properties that contribute to its versatility and indispensability. Despite often being overlooked, these properties are the key factors that make water an invaluable compound.

• Chemical Formula: Water's chemical formula, H2O, signifies the covalent bonding between hydrogen and oxygen atoms. Two hydrogen atoms form a bond with a single oxygen atom.
• Appearance: In its natural state, water is a colorless, odorless, and tasteless liquid.
• Boiling Point: Water defies the periodic table trend with its relatively high boiling point of 100°C. Unlike hydrogen telluride and hydrogen sulfide, which have low boiling points, water's strong hydrogen bonds require a substantial amount of energy to break and initiate boiling.
• Freezing Point: The same principle applies to the freezing point of water. It freezes at 0°C, and its slow freezing and boiling rates are of great significance to our ecosystem and survival.
• Density: Water exhibits a unique property where it becomes less dense in its solid state, making ice float. Until 4°C, water's density increases upon cooling, but beyond that temperature, it becomes less dense.
• Viscosity: Water possesses high viscosity due to its strong intermolecular interactions.
• Solvency: Water acts as an exceptional solvent and is commonly referred to as the Universal Solvent. Its molecular polarity enables it to dissolve nearly any substance.

Chemical Properties of Water

Amphoteric Nature: Water exhibits a remarkable amphoteric nature, which means it can function as both an acid and a base. While water itself is neither acidic nor basic, it can act as both, owing to its ability to donate and accept protons. When interacting with stronger acids, water acts as a base, whereas when encountering stronger bases, it behaves as an acid. The following reactions exemplify this amphoteric behavior:

H₂O (l) + HCl (aq) ⇌ H₃O^{+ +} Cl^-

H₂O (l) + NH₃ (aq) ⇌ NH₄⁺ + OH^-

Hydrolysis Reaction: Due to its high dielectric constant, water possesses a strong affinity for hydration. It readily engages in reactions with salt ions, forming hydrating shells around them. This phenomenon is known as hydrolysis. An example of hydrolysis is the reaction between SiCl₄ and water, resulting in the formation of SiO₂ and 4HCl:

SiCl₄ + 2H₂O → SiO₂ + 4HCl

Redox Reactions: Water serves as an excellent source for obtaining dihydrogen through reduction reactions with highly electropositive metals such as sodium. The reaction between water and sodium produces sodium hydroxide (NaOH) and hydrogen gas (H₂):

H₂O + Na → 2NaOH + H₂

Structure of Water

Closely observe the structure of a water molecule. You will see one atom of oxygen and two atoms of hydrogen. Each atom of hydrogen bonds covalently with the atom of oxygen. So both atoms of hydrogen share one pair of electrons with the oxygen atom.
Oxygen is a more electronegative element in comparison to water. This results in an uneven distribution of electron density. This gives the water molecule an angular bent structure. The H-O-H bond has a slight angle of about 104.5°. So it can be said that water molecule is polar. It has a slight negative polarity near the oxygen atom and slight positive charge near both the hydrogen atoms.

Structure of Ice

The structure of the molecules of water in its frozen form i.e. ice is very unique. It forms a Lattice Structure that does not generally occur naturally in any other substance other than ice.
When water reaches its freezing point its atoms rearrange themselves in a very specific three-dimensional pattern. The oxygen atom is surrounded by four hydrogen atoms. Two of these form O-H bonds normally seen in water molecules. The other two form a hydrogen bond.
This very special hexagonal shape is what gives ice the unique property of being less dense than water. Since in the structure of ice there are empty spaces between the hexagonal structure, its density is less than that of water in its liquid state. This is why ice floats on water.