At a Glance

Atoms, the Basic Structural Units of Matter, Are Composed of Still Smaller Particles
Electrons Orbit the Nucleus at Fixed Distances, Forming Electron Shells That Correspond to Different Energy Levels

Atoms Interact with Other Atoms When There Are Vacancies in Their Outermost Electron Shells
Charged Atoms Called Ions Interact to Form Ionic Bonds
Uncharged Atoms Can Become Stable by Sharing Electrons, Forming Covalent Bonds
Most Biological Molecules Utilize Covalent Bonding
Electron Sharing Determines Whether a Covalent Bond Is Nonpolar or Polar
Free Radicals Are Highly Reactive and Can Damage Cells
Hydrogen Bonds Are Weaker Electrical Attractions Between or Within Molecules with Polar Covalent Bonds

Water Interacts with Many Other Molecules
Water Molecules Tend to Stick Together
Water-Based Solutions Can Be Acidic, Basic, or Neutral
A Buffer Helps Maintain a Solution at a Relatively Constant pH
Water Moderates the Effects of Temperature Changes
Water Forms an Unusual Solid: Ice

Chapter 2: Atoms, Molecules, and Life