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AP Biology

AP Biology. Chapter 2 Key Concepts. Chemical Elements and Compounds. Matter--chemical elements pure form—as elements in combinations—as compounds Elements: cannot be broken down to other substances. Compounds: contain 2+ elements in a fixed ratio. Chemical Elements and Compounds.

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AP Biology

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  1. AP Biology Chapter 2 Key Concepts

  2. Chemical Elements and Compounds • Matter--chemical elements • pure form—as elements • in combinations—as compounds • Elements: cannot be broken down to other substances. • Compounds: • contain 2+ elements • in a fixed ratio

  3. Chemical Elements and Compounds • ~ 25 chemical elements required for life • ~96% of living matter composed of: • Carbon • Oxygen • Hydrogen • Nitrogen

  4. Atoms and Molecules • Atomic structure determines the behavior of an element • Atom = smallest unit of an element • Atom = nucleus (protons + neutrons) and surrounding cloud electrons • Electrically neutral atom: #electrons = #protons • Most elements have ≥ isotopes • Some isotopes are unstable  give off particles and energy as radioactivity.

  5. Atoms and Molecules • Chemical behavior of atom due to electrons • Electrons: occupy specific energy levels, or shells, of atom. • Chemical behavior: f(# valence electrons) —lncomplete valence shellatom is reactive • Electrons: in orbitals (3-D spaces; specific shapes; located in successive ‘shells’

  6. Atoms and Molecules • Molecules: combined (by chemical bonding) atoms • Chemical bonds: form when atoms interact and complete their valence shells • Covalent Bond = 2 atoms sharing 2 valence e- • Molecules: ≥covalently bonded atoms • Electrons of polar covalent bonds pulled closer to more electronegative atom • Covalent bond: nonpolar if both atoms equally electronegative.

  7. Atoms and Molecules • If electronegativity between two atoms is great enough, it can cause ≥1 e- s to be actually transferred from one atom to the other. • Anion: negatively charged ion • Cation: positively charged ion • Ionic Bond: attraction between two ions of opposite charge

  8. Atoms and Molecules • Weak chemical bonds: • Hydrogen bond: weak attraction between one electronegative atom and a hydrogen atom that is covalently linked to another electronegative atom. • Van der Waals interactions: result from transiently positive and negative regions of molecules attract each other. • Weak chemical bonds: • reinforce the shapes of large molecules • help molecules adhere to each other.

  9. Atoms and Molecules • Molecule’s biological function--related to its shape • Molecule’s shape: determined by positions of valence orbitals. • Covalent bonds: s and p orbitals (of valence shell) of atom may combine to form 4 hybrid orbital, extending to corners of a tetrahedron • e.g. shape of H2O, CH4, + many complex biological molecules. • Shape: basis of recognition of one biological molecule by another.

  10. Atoms and Molecules • Chemical reactions: • Make/break chemical bonds • Change reactants into products (while conserving matter) • Most are reversible. • Chemical equilibrium: forward and reverse reaction rates are equal.

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