Chemistry of Life: Water and Its Properties

Chemistry of Life

Organization of Life

The study of biology begins with understanding the chemical basis of life. All living things are composed of matter, which is anything that has mass and occupies space.

• Matter: Composed of atoms, the smallest part of an element that retains its properties.

• Six elements essential for life: Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, Sulfur (C, H, O, N, P, S).

• Cell: The most basic unit of life.

Water

Structure and Importance of Water

Water (H2O) is a molecule made of two hydrogen atoms covalently bonded to one oxygen atom. Water is critical for all of life's processes and has unique properties due to its molecular structure.

• Polar molecule: Water has an unequal distribution of charges, making one side more positive and the other more negative.

• Importance: Water's polarity is responsible for its special properties essential to life.

Polar and Nonpolar Molecules

Definitions and Examples

Molecules can be classified based on the distribution of electrical charge.

• Polar Molecule:

  • Unequal distribution of charges.

  • One side is more positive, the other more negative.

  • Dissolves in water.

  • Example: Water (H2O).

• Nonpolar Molecule:

  • No separation of charge; no positive or negative poles.

  • Does not dissolve in water.

  • Examples: Carbon dioxide (CO2), oxygen (O2), lipids.

Properties of Water

Key Physical and Chemical Properties

Water exhibits several important properties that make it vital for life:

• Cohesion

• Adhesion

• High specific heat

• Less dense as a solid

• Excellent solvent

Cohesion

Definition and Biological Significance

Cohesion refers to the attraction between molecules of the same substance. In water, this leads to molecules sticking together, resulting in high surface tension.

• Surface tension: The measure of how difficult it is to stretch or break the surface of a liquid.

• Example: Water droplets forming beads on a surface; insects walking on water.

Adhesion

Definition and Examples

Adhesion is the attraction between molecules of different substances. Water can form strong bonds with other materials, which is important in many biological processes.

• Stronger bonds than cohesion.

• Examples:

  • Meniscus formation in a graduated cylinder.

  • Capillary action in plants, trees, and straws.

High Specific Heat

Thermal Properties and Biological Impact

Water has a high specific heat, meaning it requires more energy to change its temperature compared to other substances.

• Regulates cell temperatures: Helps maintain stable internal conditions in organisms.

• Buffers temperature fluctuations: Keeps Earth's climate moderate and allows aquatic life to survive.

Less Dense as a Solid

Ice and Its Ecological Importance

Solid water (ice) is less dense than liquid water, so ice floats. This property is crucial for aquatic ecosystems.

• Life under ice: Aquatic organisms can survive beneath frozen surfaces of lakes and polar seas.

Water as a Solvent

Solutions, Solutes, and Solvents

Water's polarity makes it an excellent solvent, capable of dissolving a wide variety of substances.

• Solution: Uniform mixture of two or more substances.

• Solute: Substance that gets dissolved (e.g., lemonade powder).

• Solvent: Substance that does the dissolving (e.g., water).

• Universal solvent: Water dissolves more substances than any other liquid.

Hydrophilic and Hydrophobic Substances

Affinity for Water

Substances can be classified based on their interaction with water.

• Hydrophilic:

  • Has an affinity for water; water "loving".

  • Usually dissolves easily in water.

  • Examples: Salt, sugar.

• Hydrophobic:

  • Does not have an affinity for water; water "fearing".

  • Does not dissolve in water.

  • Example: Oil.

Summary Table: Properties of Water

Property	Description	Biological Importance
Cohesion	Attraction between water molecules	Surface tension, transport in plants
Adhesion	Attraction between water and other substances	Capillary action, nutrient transport
High Specific Heat	Resists temperature change	Stable environments, climate moderation
Less Dense as a Solid	Ice floats on water	Life survives under ice
Solvent Ability	Dissolves many substances	Facilitates chemical reactions

Key Equations

• Water molecule: $\mathrm{H_2O}$

• General solution equation: $\text{Solute} + \text{Solvent} \rightarrow \text{Solution}$

Additional info: The notes have been expanded to include definitions, examples, and biological significance for each property, as well as a summary table for quick review.