Chapter 2: Chemical Basis of Life – Study Notes

Study Guide - Smart Notes

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

Chapter 2: Chemical Basis of Life

Outline

This chapter explores the fundamental chemical principles underlying biological systems, focusing on the structure and properties of atoms, molecules, and chemical bonds essential for life.

1. Matter, Elements, and Compounds

Matter consists of chemical elements in pure form and in combinations called compounds.
Elements are substances that cannot be broken down into other substances by chemical means.
Compounds are substances consisting of two or more elements combined in a fixed ratio.
Elements of Life: The most common elements in living organisms are carbon (C), hydrogen (H), oxygen (O), and nitrogen (N).

2. Structure of Atoms

Subatomic Particles: Atoms are composed of protons (positive charge), neutrons (neutral), and electrons (negative charge).
Atomic Number and Atomic Mass:
- Atomic number is the number of protons in an atom.
- Atomic mass is the sum of protons and neutrons.
Isotopes: Atoms of the same element with different numbers of neutrons.
Energy Levels of Electrons: Electrons are arranged in shells around the nucleus; the chemical behavior of an atom depends on the distribution of electrons in these shells.
Electron Distributions and Chemical Properties: The outermost shell (valence shell) determines the atom's chemical properties.

3. Molecules and Chemical Bonds

Molecules are formed when two or more atoms are held together by chemical bonds.
Covalent Bonds: Atoms share pairs of electrons.
Ionic Bonds: Atoms transfer electrons, resulting in oppositely charged ions that attract each other.
Weak Chemical Bonds: Include hydrogen bonds and van der Waals interactions; important for the structure and function of large biological molecules.
Molecular Shape and Function: The shape of a molecule is crucial for its function in biological systems.

4. Chemical Reactions

Chemical reactions make and break chemical bonds, transforming reactants into products.
All chemical reactions are theoretically reversible.

Concept Checks

Emergent Properties: Explain how table salt (NaCl) has properties different from its constituent elements, sodium and chlorine.
Trace Elements: Define trace elements and explain their importance in biological systems.
Atomic Mass in Daltons: A lithium atom has 3 protons and 4 neutrons. Its atomic mass is 7 daltons (1 dalton ≈ mass of 1 proton or neutron).
Isotopes: Nitrogen-7 has 7 protons and 7 neutrons; nitrogen-8 has 7 protons and 8 neutrons. Isotopes have the same atomic number but different mass numbers.
Electron Shells: The chemical behavior of an atom depends on the number and arrangement of electrons in its electron shells.
Electron Configuration: The number of electrons in the outermost shell (valence electrons) determines chemical reactivity.
Periodic Table: Elements in the same column have the same number of valence electrons and similar chemical properties.
Structural Formula: The structural formula for methane is CH4, showing four hydrogen atoms bonded to a central carbon atom.
Three-Dimensional Shape: The three-dimensional shape of molecules is important for molecular recognition and function (e.g., enzyme-substrate interactions).
Chemical Equations: Photosynthesis can be summarized as: This equation shows the conversion of carbon dioxide and water into glucose and oxygen, driven by sunlight.
Redox Reactions: In photosynthesis, water is oxidized and carbon dioxide is reduced.
Cellular Respiration: The process by which cells break down glucose to produce energy, releasing carbon dioxide and water as byproducts.

Key Table: Comparison of Chemical Bonds

Bond Type	Description	Strength	Example
Covalent	Atoms share electron pairs	Strong	H2O (water)
Ionic	Transfer of electrons between atoms	Strong (in dry conditions)	NaCl (table salt)
Hydrogen	Attraction between a hydrogen atom and an electronegative atom	Weak	Between water molecules
Van der Waals	Weak attractions due to transient local charges	Very weak	Interactions between nonpolar molecules

Additional info:

Dalton is a unit of mass used to express atomic and molecular weights (1 dalton ≈ 1.66 × 10-24 grams).
Emergent properties are characteristics that arise from the arrangement and interaction of parts within a system.
Trace elements such as iron (Fe), iodine (I), and zinc (Zn) are required in minute amounts but are essential for life.