Chemistry of Life

Introduction

The chemistry of life explores the fundamental chemical principles and elements that form the basis of all living organisms. Understanding these concepts is essential for studying biological processes at the molecular and cellular levels.

Basic Chemical Concepts

Definitions and Key Terms

• Matter: Anything that has mass and occupies space. All living and non-living things are composed of matter.

• Element: A pure substance consisting of only one type of atom, distinguished by its atomic number (number of protons).

• Compound: A substance formed when two or more different elements are chemically bonded together in fixed proportions (e.g., H2O).

• Major Elements in Living Matter: Four elements—carbon (C), hydrogen (H), oxygen (O), and nitrogen (N)—make up about 96% of living matter.

• Essential Element: An element required for an organism to survive, grow, and reproduce.

• Trace Element: An element required by an organism in minute quantities (e.g., iron, iodine).

Atomic Structure

Structure of an Atom

• An atom consists of a central nucleus containing protons (positively charged) and neutrons (neutral), surrounded by electrons (negatively charged) in electron shells.

• Atomic Number (Z): The number of protons in the nucleus; defines the element.

• Mass Number (A): The sum of protons and neutrons in the nucleus.

• Electrons: Found in orbitals around the nucleus; their arrangement determines chemical behavior.

Example: Helium Atom

• Atomic Number: 2 (2 protons)

• Mass Number: 4 (2 protons + 2 neutrons)

• Electrons: 2

Subatomic Particles

• Neutron: Neutral particle in the nucleus; mass ≈ 1 atomic mass unit (amu).

• Proton: Positively charged particle in the nucleus; mass ≈ 1 amu.

• Electron: Negatively charged particle; mass is negligible compared to protons and neutrons.

Energy and Electrons

• Energy: The capacity to do work or cause change. In atoms, electrons have potential energy based on their position relative to the nucleus.

• Potential Energy: Stored energy due to position or structure. Electrons further from the nucleus have higher potential energy.

The Periodic Table and Elements

Reading the Periodic Table

• Each element is represented by a symbol (e.g., C for carbon), atomic number, and atomic mass.

• Example: Carbon (C) has atomic number 6 and atomic mass 12.011.

Valence Electrons and Chemical Behavior

• Valence Electrons: Electrons in the outermost shell; determine how atoms interact and bond.

• Atoms with full valence shells are chemically inert (e.g., noble gases).

Isotopes

Definition and Applications

• Isotope: Atoms of the same element with different numbers of neutrons, thus different mass numbers.

• Radioactive Isotope: An isotope with an unstable nucleus that decays, emitting radiation. Used in medical imaging and dating fossils.

• Example: Carbon-12 and Carbon-14 are isotopes of carbon; Carbon-14 is radioactive and used in radiocarbon dating.

Chemical Bonds

Covalent Bonds

• Covalent Bond: A chemical bond formed when two atoms share one or more pairs of electrons.

• Non-polar Covalent Bond: Electrons are shared equally (e.g., O2 molecule).

• Polar Covalent Bond: Electrons are shared unequally, resulting in partial charges (e.g., H2O).

Ionic Bonds

• Ionic Bond: Formed when one atom transfers electrons to another, creating oppositely charged ions that attract each other (e.g., NaCl).

• Anion: Negatively charged ion (gains electrons).

• Cation: Positively charged ion (loses electrons).

Hydrogen Bonds

• Hydrogen Bond: A weak bond between a hydrogen atom covalently bonded to an electronegative atom (like oxygen or nitrogen) and another electronegative atom.

• Important in stabilizing the structure of water, proteins, and DNA.

Electronegativity

• Electronegativity: The ability of an atom to attract shared electrons in a covalent bond.

• Oxygen is highly electronegative, making water a polar molecule.

Structural and Molecular Formulas

• Molecular Formula: Shows the types and numbers of atoms in a molecule (e.g., H2O).

• Structural Formula: Shows the arrangement of atoms and bonds (e.g., H–O–H for water).

Table: Molecules and Compounds

Photosynthesis

Equation and Components

• Photosynthesis: The process by which plants, algae, and some bacteria convert light energy into chemical energy.

• General Equation:

• Reactants: Carbon dioxide (CO2), water (H2O), and light energy

• Products: Glucose (C6H12O6) and oxygen (O2)

Properties of Water

Structure and Polarity

• Water is a polar molecule with a bent shape, resulting in partial positive (H) and partial negative (O) charges.

• Hydrogen bonds form between water molecules, leading to unique properties.

Cohesion and Adhesion

• Cohesion: Attraction between molecules of the same substance (e.g., water molecules stick together).

• Adhesion: Attraction between molecules of different substances (e.g., water to glass).

Ice and Liquid Water

• Ice floats because its hydrogen bonds form a crystalline structure, making it less dense than liquid water.

• Hydrogen bonds in liquid water are constantly breaking and reforming, allowing molecules to be closer together.

Aqueous Solutions

• Aqueous Solution: A solution in which water is the solvent.

Acids, Bases, and pH

pH Scale

• pH: A measure of hydrogen ion (H+) concentration; scale ranges from 0 (most acidic) to 14 (most basic).

• Each pH unit represents a tenfold difference in H+ concentration.

• Human blood pH is tightly regulated around 7.4.

Buffers

• Buffer: A substance that minimizes changes in pH by accepting or donating H+ ions.

• Example: Bicarbonate buffer system in blood.

Buffer System Equation

• When pH rises (less H+), carbonic acid (H2CO3) donates H+.

• When pH drops (more H+), bicarbonate (HCO3-) accepts H+.

Ocean Acidification

Process and Impact

• When CO2 dissolves in seawater, it forms carbonic acid, which lowers ocean pH (acidification).

• This disrupts the balance of carbonate ions, affecting marine organisms that build shells and skeletons from calcium carbonate (CaCO3).

Key Reactions in Ocean Acidification

• Increased H+ reduces CO32- availability, making it harder for organisms to form CaCO3 structures.

Summary Table: Key Terms and Definitions

Additional info: Some explanations and examples have been expanded for clarity and completeness, including the summary tables and detailed chemical equations.