Chapter 2: The Chemical Context of Life - Study Notes

Chapter 2: The Chemical Context of Life

Concept 2.1: Matter Consists of Chemical Elements in Pure Form and in Combinations Called Compounds

The study of biology requires an understanding of the chemical basis of life. Matter is composed of elements, which can combine to form compounds essential for biological processes.

• Matter: Anything that takes up space and has mass.

• Element: A substance that cannot be broken down to other substances by chemical reactions.

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

• Essential Elements: Elements required for an organism to survive, grow, and reproduce (e.g., carbon, hydrogen, oxygen, nitrogen).

• Trace Elements: Elements required in minute quantities (e.g., iron, iodine).

• Example: Water (H2O) is a compound made of hydrogen and oxygen.

Concept 2.2: An Element’s Properties Depend on the Structure of Its Atoms

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

• Atom: The smallest unit of an element, composed of protons, neutrons, and electrons.

• Atomic Number: Number of protons in the nucleus.

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

• Isotopes: Variants of an element with different numbers of neutrons.

• Radioactive Isotopes: Isotopes that decay spontaneously, giving off particles and energy.

• Example: Carbon-12 and Carbon-14 are isotopes of carbon.

• Formula: $\text{Mass Number} = \text{Number of Protons} + \text{Number of Neutrons}$

Concept 2.3: The Formation and Function of Molecules Depend on Chemical Bonding Between Atoms

Chemical bonds form between atoms to create molecules. The type of bond affects the properties and functions of molecules in biological systems.

• Covalent Bond: Sharing of a pair of valence electrons by two atoms.

• Ionic Bond: Transfer of electrons from one atom to another, resulting in charged ions.

• Hydrogen Bond: Weak attraction between a hydrogen atom 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 molecules are held together by hydrogen bonds.

• Additional info: Covalent bonds can be single, double, or triple depending on the number of shared electron pairs.

Concept 2.4: Chemical Reactions Make and Break Chemical Bonds

Chemical reactions involve the making and breaking of chemical bonds, leading to changes in the composition of matter.

• Chemical Reaction: The process of making and breaking chemical bonds, leading to changes in the composition of matter.

• Reactants: Starting materials in a chemical reaction.

• Products: Ending materials in a chemical reaction.

• Example: Photosynthesis is a chemical reaction where carbon dioxide and water are converted into glucose and oxygen.

• Formula: $\text{Reactants} \rightarrow \text{Products}$

• Additional info: Chemical equilibrium is reached when the forward and reverse reactions occur at the same rate.