Chapter 2: The Chemical Context of Life

2.1 Matter, Elements, and Emergent Properties

This section introduces the basic building blocks of matter and the concept of emergent properties in biological systems.

• Matter: Anything that occupies space and has mass.

• Element: A substance that cannot be broken down into other substances by chemical means. Each element is distinguished by its number of protons.

• Compound: A substance consisting of two or more elements combined in a fixed ratio.

• Emergent Property: A property that arises when components interact, which is not present in the individual components. Example: Table salt (NaCl) has properties different from sodium and chlorine alone.

2.2 Structure of Atoms

Atoms are the smallest units of matter that retain the properties of an element. Their structure determines chemical behavior.

• Atom: Composed of protons, neutrons, and electrons.

• Proton: Positively charged particle in the nucleus.

• Neutron: Neutral particle in the nucleus.

• Electron: Negatively charged particle orbiting the nucleus.

• Dalton: Unit of atomic mass (also called atomic mass unit, amu).

• Atomic Number: Number of protons in the nucleus; defines the element.

• Mass Number: Sum of protons and neutrons in the nucleus.

• Atomic Mass: The total mass of an atom, often approximated by the mass number.

• Electron Shell: Energy levels where electrons are found.

• Valence Electron: Electrons in the outermost shell; determine chemical reactivity.

• Valence Shell: The outermost electron shell.

• Energy of Electrons: Electrons farther from the nucleus have higher energy.

Example: Carbon has 6 protons, 6 neutrons, and 6 electrons. Its atomic number is 6, and its mass number is 12.

Additional info: Electron distribution diagrams help visualize how electrons fill shells.

2.3 Chemical Bonds and Interactions

Atoms form chemical bonds to achieve stable electron configurations. The type of bond affects molecular properties.

• Chemical Bond: Attraction between atoms that enables the formation of chemical substances.

• Covalent Bond: Sharing of electron pairs between atoms.

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

• Nonpolar Covalent Bond: Electrons are shared equally (e.g., C-H bond).

• Polar Covalent Bond: Electrons are shared unequally due to differences in electronegativity (e.g., O-H bond).

• Ion: Atom or molecule with a net electric charge due to loss or gain of electrons.

• Anion: Negatively charged ion.

• Cation: Positively charged ion.

• Ionic Bond: Attraction between oppositely charged ions.

• Hydrogen Bond: Weak attraction between a hydrogen atom (in a polar bond) and another electronegative atom.

• Van der Waals Interactions: Weak attractions between molecules or parts of molecules that result from transient local partial charges.

Example: Water (H2O) has polar covalent bonds between O and H, and forms hydrogen bonds with other water molecules.

Additional info: Oxygen is highly electronegative and forms polar bonds with C, H, and N.

2.4 Chemical Reactions and Equilibrium

Chemical reactions involve the making and breaking of chemical bonds, transforming reactants into products.

• Chemical Reaction: Process in which substances (reactants) are transformed into different substances (products).

• Reactants: Starting materials in a chemical reaction.

• Products: Substances formed as a result of a chemical reaction.

• Chemical Equilibrium: State in which the rate of the forward reaction equals the rate of the reverse reaction; concentrations of reactants and products remain constant.

Example:

Additional info: Visual skills and concept checks help identify reactants and products in reactions.

2.5 Properties of Water and Acids/Bases

Water's unique properties are essential for life, largely due to its structure and ability to form hydrogen bonds.

• Hydrogen Bonds in Water: Each water molecule can form up to four hydrogen bonds with neighboring molecules.

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

• Adhesion: Attraction between molecules of different substances (e.g., water and plant cell walls).

• Surface Tension: Measure of how difficult it is to break the surface of a liquid.

• Temperature: Average kinetic energy of molecules.

• Heat: Total kinetic energy due to molecular motion.

• Specific Heat: Amount of heat required to change the temperature of 1 gram of a substance by 1°C.

• Heat of Vaporization: Amount of heat required to convert 1 gram of a liquid to gas.

• Solution: Homogeneous mixture of two or more substances.

• Solvent: The dissolving agent (e.g., water).

• Solute: The substance dissolved.

• Aqueous: Solution where water is the solvent.

• Hydrophilic: Substances that have an affinity for water.

• Hydrophobic: Substances that repel water.

• Acid: Substance that increases the hydrogen ion (H+) concentration.

• Base: Substance that reduces the hydrogen ion concentration.

• pH: Measure of hydrogen ion concentration; scale ranges from 0 (acidic) to 14 (basic).

Example: Ice floats because it is less dense than liquid water due to hydrogen bonding.

Additional info: Water is a good solvent because its polarity allows it to dissolve many substances.

Table: Types of Chemical Bonds and Their Properties

Table: Acids, Bases, and pH Scale

Key Equations

• Atomic Number:

• Mass Number:

• pH Calculation: