I. What are atoms? A. B. C. Basic structural Units of matter Composed of still smaller particles Terms to know 1. 2. 3. 4. 5. II. 6. 7. 8. 9. 10. 11. atoms atomic nucleus protons neutrons electrons a) Orbit the nucleus at fixed distances b) Form electron shells that correspond to different energy levels element atomic number isotopes radioactive isotopes electron shells bonds How do atoms interact to form molecules? A. B. Only when vacancies in outermost electron shells Terms to know 1. 2. 3. 4. C. Chemical Bonds 1. 2. D. Weak bonds a) Allow interactions between individual atoms or molecules b) ionic c) hydrogen d) hydrophobic Strong bonds a) Hold atoms together within molecules b) covalent bonds Charged atoms 1. 2. 3. E. molecule compound chemical bonds chemical reactions Called Ions Interact to form ionic bonds Terms to know a) ions b) ionic bond Uncharged atoms 1. 2. Become stable by sharing electrons Form covalent bonds a) nonpolar covalent bonds are electrically symmetrical 3. F. III. Hydrogen bonds 1. 2. Weaker electrical attractions Between or within molecules with polar covalent bonds Why is water so important to life? A. It interacts with many other molecules 1. 2. 3. 4. B. C. cohesion surface tension It can form H+ and OH- ions 1. 2. 3. 4. 5. 6. D. solvent hydrophilic hydrophobic hydrophobic interaction Its molecules tend to stick together 1. 2. acidic acid basic base pH scale buffer maintains a solution at a relatively constant pH It moderates the effects of temperature changes 1. 2. 3. 4. IV. b) polar covalent bonds form when atoms share electrons unequally Most biological molecules use covalent bonding calorie specific heat heat of vaporization heat of fusion E. It forms a solid: ice A. B. C. D. free radicals oxidative stress antioxidants flavenoids Case Studies: Health Food