The Chemistry of Life

I. Chemistry and Matter

Chemistry is the study of matter and the chemical reactions that govern its behavior. Matter is anything that occupies space and has mass, existing in three states: solid, liquid, and gas.

• Matter: Anything that occupies space and has mass.

• States of Matter: Solid, liquid, gas.

• Mass: For practical purposes on Earth, mass is equivalent to weight.

II. Elements and Atoms

Elements are pure substances that cannot be broken down into simpler substances by ordinary chemical means. Atoms are the smallest units of elements, and their structure determines the properties of elements and compounds.

• Element: A substance that cannot be broken down into simpler substances by ordinary chemical means. There are 94 naturally occurring elements on Earth.

• Compound: A substance formed when two or more elements combine chemically (e.g., CO2, HCl, C6H12O6).

• Atom: The smallest unit of an element, consisting of a nucleus (protons and neutrons) and electrons orbiting the nucleus.

Structure of the Atom

• Nucleus: Contains protons and neutrons; almost all the mass of the atom is here.

• Protons: Positively charged particles; the number of protons equals the atomic number and defines the element.

• Neutrons: Neutral particles; contribute to atomic mass but not charge.

• Electrons: Negatively charged particles with negligible mass; orbit the nucleus in energy shells.

Atomic Mass: The sum of protons and neutrons in the nucleus.

Electron Configuration: Electrons fill energy shells in a specific order (e.g., 2 in the first shell, 8 in the second, etc.). The outermost electrons are called valence electrons and are involved in chemical bonding.

• Example (Sodium, Na): Atomic number 11; electron configuration 2/8/1; 1 valence electron.

• Example (Carbon, C): Atomic number 6; electron configuration 2/4; 4 valence electrons.

Octet Rule: Atoms are most stable when they have 8 electrons in their outer shell (like noble gases).

III. Types of Chemical Bonds

Atoms combine to form molecules through different types of chemical bonds, which determine the properties of compounds.

• Ionic Bonds: Formed when one atom donates an electron to another, resulting in oppositely charged ions that attract each other.

  • Example: Na (donates 1 electron) + Cl (accepts 1 electron) → Na+ + Cl-

  • Atoms that lose electrons become cations (positive), those that gain become anions (negative).

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

  • Nonpolar Covalent Bonds: Equal sharing of electrons (e.g., methane, CH4); usually hydrophobic (do not dissolve in water).

  • Polar Covalent Bonds: Unequal sharing of electrons due to differences in electronegativity (e.g., water, H2O); usually hydrophilic (dissolve in water).

• Hydrogen Bonds: Weak attractions between a hydrogen atom in one molecule and an electronegative atom (like O or N) in another. Not true bonds, but important for the properties of water.

Properties of Water Due to Hydrogen Bonds

• Cohesion: Water molecules stick to each other (surface tension).

• Adhesion: Water molecules stick to other substances.

• High Heat Capacity: Water absorbs heat, moderating Earth's temperature.

• Ice Floats: Solid water is less dense than liquid, insulating aquatic life.

IV. Organic Molecules and Macromolecules

Organic molecules are based on carbon backbones and contain at least one C-H bond. They form the basis of life and include four major classes of macromolecules.

• Organic Molecule: Contains a carbon backbone and at least one C-H bond (e.g., CH4, C2H6).

The Four Macromolecules

• Carbohydrates:

  • Monomer: Monosaccharide (e.g., glucose).

  • Polymer: Polysaccharide (e.g., starch).

  • Function: Primary energy source for most organisms.

• Proteins:

  • Monomer: Amino acids (20 types).

  • Structure: Amino acids linked in chains, folded into 3D shapes; shape determines function.

  • Functions: Structural support, enzymes, antibodies, membrane receptors, carrier proteins.

• Nucleic Acids:

  • Monomer: Nucleotide (phosphate group + 5-carbon sugar + nitrogenous base).

  • Example: DNA (double helix), stores genetic information.

• Lipids:

  • Fats (Triglycerides): Long-term energy storage, insulation, organ protection; hydrophobic.

  • Phospholipids: Main component of cell membranes; have hydrophilic heads and hydrophobic tails, forming a bilayer.

  • Note: Lipids do not have true monomers.

V. Acids, Bases, and pH

The pH scale measures the concentration of hydrogen ions (H+) in a solution, indicating its acidity or basicity.

• pH Definition:

• Acid: Increases H+ concentration in solution.

• Base: Decreases H+ concentration in solution.

• pH Scale: Ranges from 0 (most acidic) to 14 (most basic); 7 is neutral.

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

• Example: A solution with pH 2 is 1,000,000 times more acidic than one with pH 8.

VI. Properties of Living Things

All living organisms share certain fundamental properties that distinguish them from non-living matter.

• Reproduction: Ability to produce new individuals.

• Growth: Increase in size and complexity.

• Response to Stimuli: Ability to sense and react to environmental changes.

• Homeostasis: Maintenance of a stable internal environment despite external changes.

• Energy Requirement: All living things require a source of energy to carry out life processes.

Additional info: The above notes expand on the original study guide by providing definitions, examples, and explanations for key concepts in the chemistry of life, suitable for introductory college biology students.