Chemical Foundations of Life: Atoms, Bonds, and Water in Biology

Chemical Foundations of Life

Atomic Structure and Components

The structure of atoms forms the basis for understanding chemical properties and biological functions. Atoms are composed of three main subatomic particles:

• Protons: Positively charged particles located in the nucleus.

• Neutrons: Neutral particles also found in the nucleus.

• Electrons: Negatively charged particles that orbit the nucleus in electron shells.

Example: A carbon atom has 6 protons, 6 neutrons, and 6 electrons.

Ions and Isotopes

• Ions are atoms or molecules that have gained or lost electrons, resulting in a net charge.

• Isotopes are atoms of the same element with different numbers of neutrons, affecting their mass but not their chemical properties.

Example: Carbon-12 and Carbon-14 are isotopes of carbon.

Valence Electrons and Bonding

Valence electrons are the outermost electrons of an atom and determine its bonding behavior.

• Atoms with incomplete valence shells tend to form chemical bonds to achieve stability.

Types of Chemical Bonds

• Ionic Bonds: Formed when electrons are transferred from one atom to another, creating charged ions.

• Covalent Bonds: Formed when two atoms share one or more pairs of electrons.

• Hydrogen Bonds: Weak attractions between a hydrogen atom covalently bonded to an electronegative atom (like oxygen or nitrogen) and another electronegative atom.

Importance in Biology: These bonds determine the structure and function of biological molecules.

Polar vs. Nonpolar Molecules

Polar molecules have an uneven distribution of charge due to differences in electronegativity between atoms, resulting in partial positive and negative ends. Nonpolar molecules have an even distribution of charge.

• Biological Relevance: Polarity affects solubility, membrane formation, and molecular interactions in cells.

Example: Water (H2O) is polar; oxygen (O2) is nonpolar.

Properties of Water

• Water's polarity allows it to form hydrogen bonds, making it an excellent solvent for ionic and polar substances.

• Key properties: cohesion, adhesion, high specific heat, and ability to dissolve many substances.

Example: Water dissolves salts and sugars but not oils (which are nonpolar).

pH and Acidity

The pH scale (0-14) measures the concentration of hydrogen ions (H+) in a solution:

• Acidic: pH < 7

• Neutral: pH = 7

• Basic (Alkaline): pH > 7

Each whole number change on the pH scale represents a tenfold change in H+ concentration.

Functional Groups in Organic Molecules

Functional groups are specific groups of atoms within molecules that determine the chemical properties and reactions of those molecules.

• Common functional groups: hydroxyl, carboxyl, amino, phosphate, and methyl groups.

• They influence molecular polarity, reactivity, and interactions.

Example: The carboxyl group (-COOH) makes molecules acidic.

Chemical Properties and Biological Function

• The chemical properties of molecules, such as polarity and functional groups, influence their roles in cellular processes and structures.

• Polarity affects membrane formation, protein folding, and enzyme activity.

Example: Phospholipids have polar heads and nonpolar tails, allowing them to form cell membranes.

Table: Comparison of Bond Types

Bond Type	Description	Example
Ionic	Transfer of electrons; forms ions	NaCl (table salt)
Covalent	Sharing of electron pairs	H2O (water)
Hydrogen	Weak attraction between polar molecules	Between water molecules

Key Equations

• pH calculation: $pH = -\log_{10}[H^+]$