Atoms, Ions, Molecules, and Water: Foundations of General Biology

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Atoms, Ions, & Molecules: The Building Blocks of Chemical Evolution

Atoms: Structure and Properties

Atoms are the smallest identifiable units of matter and form the basis of all chemical substances. Understanding atomic structure is essential for grasping biological chemistry.

Atom: The smallest unit of an element, consisting of a nucleus (protons and neutrons) and electrons.
Element: A substance composed entirely of one type of atom. Examples: Hydrogen (H), Carbon (C), Nitrogen (N), Oxygen (O).
Proton: Positively charged particle in the nucleus.
Neutron: Neutral particle in the nucleus.
Electron: Negatively charged particle orbiting the nucleus.
Atomic Number: Number of protons in the nucleus; defines the element.
Mass Number: Sum of protons and neutrons in the nucleus.
Isotope: Atoms of the same element with different numbers of neutrons.
Radioactive Isotope: Unstable isotopes that decay, emitting radiation.

Example: Carbon-12 and Carbon-14 are isotopes of carbon, differing in neutron number.

Chemical Bonds: How Atoms Combine

Chemical bonds are forces that hold atoms together in molecules and compounds. The main types are covalent and ionic bonds.

Covalent Bond: Atoms share pairs of electrons. Can be single, double, or triple bonds.
Polar Covalent Bond: Electrons are shared unequally, resulting in partial charges (e.g., H2O).
Nonpolar Covalent Bond: Electrons are shared equally (e.g., H2).
Ionic Bond: Electrons are transferred from one atom to another, creating ions (charged atoms).
Ion: An atom or molecule that has gained or lost electrons, acquiring a charge.
Cation: Positively charged ion (lost electrons).
Anion: Negatively charged ion (gained electrons).
Electronegativity: Measure of how strongly an atom attracts electrons in a bond.

Example: Sodium (Na) transfers an electron to chlorine (Cl), forming Na+ and Cl- ions in NaCl.

Representing Molecules

Molecules can be represented in various ways to illustrate their structure and properties.

Molecular Formula: Indicates the number and types of atoms (e.g., H2O).
Structural Formula: Shows how atoms are bonded together.
Ball-and-Stick Model: 3D representation showing relative positions and bonds.
Space-Filling Model: 3D model showing spatial relationships and relative sizes.

Properties of Water

Water: Essential for Life

Water is the most abundant molecule in living cells and has unique properties that support life.

Water Composition: Two hydrogen atoms covalently bonded to one oxygen atom (H2O).
Polarity: Water is a polar molecule, with partial positive and negative charges.
Hydrogen Bonds: Weak attractions between the partial charges of water molecules.
Solvent: Water dissolves many substances, forming solutions.
Solution: Homogeneous mixture of solvent and solute(s).

Example: Table salt (NaCl) dissolves in water, forming a saline solution.

Unique Properties of Water

Water's structure leads to several important physical and chemical properties.

Specific Heat: Amount of energy required to raise the temperature of 1 gram of water by 1°C.
Heat of Vaporization: Energy required to convert water from liquid to gas.
Cohesion: Water molecules stick together due to hydrogen bonding.
Adhesion: Water molecules stick to other substances.
Surface Tension: Cohesive force at the surface of water, allowing it to resist external force.
Hydrophilic: "Water-loving" substances that dissolve easily in water.
Hydrophobic: "Water-fearing" substances that do not dissolve in water.

Example: Water beads on a waxed car due to surface tension.

Chemical Reactions in Water

Many biological reactions occur in aqueous solutions, including dissociation and equilibrium reactions.

Chemical Reaction: Process in which substances are combined or broken apart to form new substances.
Dissociation Reaction: Water molecules split into ions (H+ and OH-).
Chemical Equilibrium: State in which the rate of the forward and reverse reactions are equal.
Acid: Compound that donates protons (H+) in solution.
Base: Compound that accepts protons or releases hydroxide ions (OH-).
pH: Measure of hydrogen ion concentration; scale from 0 (acidic) to 14 (basic).
Buffer: Compound that minimizes changes in pH by accepting or donating H+.

Example: Blood contains buffers to maintain a stable pH.

Organic Molecules and Polymerization

Organic Compounds: The Chemistry of Life

Organic compounds are molecules containing carbon and are fundamental to biological systems.

Organic Compound: Molecule containing at least one carbon atom.
Macromolecule: Large molecule made up of smaller subunits (monomers).
Monomer: Small molecule that can join with others to form polymers.
Polymer: Large molecule made by linking monomers together.
Polymerization: Process of joining monomers to form a polymer.
Functional Group: Specific group of atoms within a molecule that imparts characteristic properties.

Example: Proteins are polymers made from amino acid monomers.

Condensation and Hydrolysis Reactions

Macromolecules are formed and broken down by specific chemical reactions.

Condensation (Dehydration) Reaction: Two monomers join, releasing a water molecule.
Hydrolysis Reaction: Polymer is broken down into monomers by adding water.

Equation:

Functional Groups in Organic Molecules

Functional groups determine the chemical reactivity and properties of organic molecules.

Hydroxyl (-OH): Polar, forms hydrogen bonds.
Carboxyl (-COOH): Acts as an acid.
Amino (-NH2): Acts as a base.
Phosphate (-PO4): Transfers energy.
Sulfhydryl (-SH): Forms disulfide bonds in proteins.

Example: Amino acids contain both amino and carboxyl groups.

Summary Table: Types of Chemical Bonds

Bond Type	Electron Sharing/Transfer	Example
Covalent (Nonpolar)	Equal sharing	H2
Covalent (Polar)	Unequal sharing	H2O
Ionic	Electron transfer	NaCl
Hydrogen Bond	Attraction between partial charges	Between water molecules

Key Equations and Constants

Avogadro's Number: molecules/mol
Molecular Weight: Sum of atomic weights of all atoms in a molecule
Concentration:

Additional info: Some explanations and examples have been expanded for clarity and completeness.