Biology Chapter 2: The Chemical Context of Life

Chapter 2: The Chemical Context of Life

• Living organisms are subject to the laws of physics and chemistry.
• Biology is a multidisciplinary science.
• Life is organized into a hierarchy of structural levels: atoms, molecules, cells, etc.
• Elements are substances that cannot be broken down.
• There are 92 naturally occurring elements.
• Each element has a unique symbol.
• A compound is a substance made of two or more elements in a fixed ratio (e.g., NaCl).
• The properties of a compound differ from those of its constituent elements.

Concept 2.1: Matter and Elements

• Matter is anything that takes up space and has mass.
• Matter is made of elements.
• Elements are made of atoms.
• Atoms consist of subatomic particles (protons, neutrons, electrons).

Concept 2.2: Atomic Structure

• Atoms are mostly empty space.
• Atomic nucleus contains protons and neutrons.
• Electrons surround the nucleus.
• Mass of a proton or neutron is close to 1 dalton.
• Mass of an electron is about 1/2000th of a proton or neutron.
• Atoms have equal numbers of protons and electrons, thus no net charge.
• Atomic number is the number of protons in an atom's nucleus.
• Isotopes are atoms of the same element that differ in the number of neutrons.
• Radioactive isotopes are unstable; they spontaneously decay, emitting particles and energy.
• Mass number is the sum of protons and neutrons in an atom's nucleus.
• Atomic mass is the average mass of an atom's isotopes.

Electron Configuration

• Electrons occupy energy levels (shells) around the nucleus.
• The first shell holds a maximum of 2 electrons.
• Higher shells can hold more electrons than the first shell.
• The chemical behaviour of an atom is determined by its electron configuration.
• Valence electrons are those in the outermost shell.
• Atoms with complete valence shells are unreactive (inert).
• Valence refers to the number of unpaired electrons in the outermost shell of an atom.

Concept 2.3: Chemical Bonding

• Atoms with incomplete valence shells interact with each other through sharing or transferring valence electrons.
• Covalent bonds form when atoms share one or more pairs of valence electrons.
• Ionic bonds form when one atom completely transfers an electron to another, creating ions.
• Hydrogen bonds involve an attraction between a hydrogen atom with a partial positive charge and an electronegative atom.
• Van der Waals interactions are weak, fleeting attractions occurring between temporarily positive and negative regions of molecules.

Concept 2.4: Chemical Reactions

• Chemical reactions make and break chemical bonds.
• Reactants are the starting molecules in a reaction; products are the resulting molecules.
• Matter is conserved in chemical reactions. Chemical reactions do not create or destroy matter.
• Some reactions go to completion but others reach a state of equilibrium. Equilibrium is reached when the rate of product formation equals the rate of reactant formation.

Explore the fundamental concepts of chemistry that underpin biological processes in this quiz focused on Chapter 2. Learn about matter, elements, and atomic structure, and discover how they relate to the organization of life. This quiz will test your understanding of these foundational topics in biology.