The Chemical Context of Life: Foundations of Biological Chemistry

Study Guide - Smart Notes

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

The Chemical Context of Life

Introduction

The study of biology begins with understanding the chemical basis of life. Atoms and molecules form the foundation of biological chemistry and are the building blocks of all living things.

Elements Essential to Life

Major and Minor Elements

Four elements—carbon (C), hydrogen (H), nitrogen (N), and oxygen (O)—make up about 96% of an organism's body mass.
Other important elements include phosphorus (P), sulfur (S), calcium (Ca), and potassium (K), which constitute most of the remaining 4%.
Trace elements are required in very small amounts but are essential for life (e.g., iron, iodine).
Element: A substance that cannot be broken down into simpler substances by chemical means.

The Periodic Table

Organization and Use

The Periodic Table of Elements organizes elements by atomic number and chemical properties.
Elements in the same column (group) have similar chemical behaviors due to the same number of valence electrons.

Compounds

Definition and Properties

Compound: Formed when two or more different elements combine in a fixed ratio (e.g., NaCl, CH4).
Compounds have physical and chemical properties different from the elements that compose them.
Compounds cannot be broken down by physical means, but can be broken down by chemical means.

Atomic Structure

Subatomic Particles

Protons: Positively charged, located in the nucleus.
Neutrons: No charge, located in the nucleus.
Electrons: Negatively charged, found outside the nucleus in orbitals; essentially massless compared to protons and neutrons.
Dalton (amu): Unit of atomic mass.

Atomic Number and Mass

Atomic number: Number of protons in the nucleus.
Atomic mass: Sum of protons and neutrons.
Example: (Carbon-12): 6 protons, 6 neutrons, atomic mass = 12

Isotopes

Definition and Applications

Isotopes: Atoms of the same element with different numbers of neutrons.
Example: , , (all have 6 protons, but different neutrons)
Radioactive isotopes (e.g., Carbon-14) emit particles and energy; used in medical imaging and carbon dating.

Electrons and Ions

Electron Configuration

In a neutral atom, the number of electrons equals the number of protons.
Atoms can lose or gain electrons to become ions and achieve stability.
Cation: Positively charged ion (loss of electrons).
Anion: Negatively charged ion (gain of electrons).

Electron Orbitals

Electrons occupy energy levels or "shells":
- 1st level: 2 electrons
- 2nd level: 8 electrons
- 3rd level: 8 electrons
- 4th level: 18 electrons
Example: Phosphorus (15 electrons): 1st shell = 2, 2nd shell = 8, 3rd shell = 5

Valence Electrons and Chemical Properties

Role in Reactivity

Valence electrons: Electrons in the outermost shell; determine chemical properties and reactivity.
Elements in the same group have the same number of valence electrons and similar chemical behavior.

Chemical Bonds

Covalent Bonds

Covalent bond: Electrons are shared between atoms.
Molecule: Compound in which atoms are held together by covalent bonds.
Single, double, and triple covalent bonds are possible.
Carbon is notable for forming stable covalent bonds.

Polar vs Nonpolar Covalent Bonds

Electronegativity: The attraction an atom has for electrons in a covalent bond.
Nonpolar covalent bond: Electrons are shared equally (e.g., O2, H2).
Polar covalent bond: Electrons are shared unequally due to differences in electronegativity (e.g., H2O).

Ionic Bonds

Ionic bond: Formed when atoms transfer electrons, resulting in attraction between cations and anions.
Ionic compounds are called "salts" (e.g., NaCl).

Chemical Reactions

Making and Breaking Bonds

Chemical reactions involve the making and breaking of chemical bonds.
Reactants are transformed into products.
Example reaction:
Reactions can be reversible; chemical equilibrium occurs when forward and reverse rates are equal.

Compound vs Molecule

Definitions and Differences

Molecule: Two or more atoms bonded together (can be the same element, e.g., O2).
Compound: A molecule composed of two or more different elements (e.g., H2O, NaCl).
All compounds are molecules, but not all molecules are compounds.

Summary Table: Key Terms and Definitions

Term	Definition	Example
Element	Substance that cannot be broken down by chemical means	Oxygen (O)
Compound	Substance formed by two or more different elements in a fixed ratio	Water (H2O)
Molecule	Two or more atoms bonded together	Oxygen molecule (O2)
Isotope	Atoms of the same element with different numbers of neutrons	Carbon-12, Carbon-14
Covalent bond	Bond formed by sharing electrons	H2O
Ionic bond	Bond formed by transfer of electrons	NaCl
Valence electron	Electron in the outermost shell	Carbon has 4 valence electrons

Additional info: Academic context and definitions have been expanded for clarity and completeness.