🧬 1. Chemical Basis of Life

Chemical origin of life

The process by which living systems may have developed from nonliving chemicals.

Simple molecules on early Earth reacted to form increasingly complex organic molecules that eventually led to life.

Covalent bond

Definition: A chemical bond formed by sharing electrons.

Atoms share one or more pairs of electrons.

Noncovalent interactions

Definition: Attractions between molecules or parts of molecules that do not involve sharing electrons.

Hydrogen bonds, ionic interactions, hydrophobic interactions, and van der Waals forces.

Ionic bond

Definition: Attraction between oppositely charged ions.

Forms when electrons are transferred from one atom to another, creating charged ions.

Balancing ionic compounds

Definition: Making the total charge of an ionic compound equal zero.

Use subscripts so positive and negative charges cancel.

Example: Mg²⁺ + 2Cl⁻ → MgCl₂

Polar molecule

Definition: A molecule with an uneven distribution of charge.
Has partial positive and partial negative regions.

Nonpolar molecule

Definition: A molecule with an even distribution of charge.
Does not have significant partial positive or negative regions.

Electronegativity

Definition: The ability of an atom to attract electrons.
Higher electronegativity means a stronger attraction for shared electrons.

“Electron dogs”

Definition: Your class term involving electron behavior.
Electrons are attracted toward positively charged nuclei; differences in attraction help determine bond polarity.

Hydrophobic

Definition: A substance that does not interact favorably with water.
Usually nonpolar and tends to avoid water.

Hydrophobic molecules in aqueous solution

Definition: How water interacts with nonpolar molecules.
Hydrophobic molecules cluster together to minimize contact with water.

Amphipathic molecule

Definition: A molecule containing both hydrophilic and hydrophobic regions.
Has one part that interacts with water and another part that avoids water.

Van der Waals forces

Definition: Weak attractions caused by temporary changes in electron distribution.
Weak attractions between nearby atoms or molecules.

Acid

Definition: A substance that increases H⁺ concentration.
Donates H⁺ or increases hydrogen ions in solution.

Base

Definition: A substance that decreases H⁺ concentration.

Accepts H⁺ or decreases hydrogen ions in solution.

pH

Definition: A measure of hydrogen/hydronium ion concentration. Indicates how acidic or basic a solution is.

pH scale

Definition: A scale used to measure acidity and basicity.
Usually 0–14; below 7 is acidic, 7 is neutral, and above 7 is basic.

pH logarithmic scale

Definition: The relationship between pH and H⁺ concentration.
Each 1-unit change in pH represents a 10× change in H⁺ concentration.