2. The CHEMISTRY of Life CHEMISTRY is the foundation of BIOLOGY.

5. Elements in the same column have the same valence & similar chemical properties

6. REACTIVITY Atoms tend to complete a partially filled valence shell or empty a partially filled valence shell – – – REACTION (Bond formation)

7. Biological Bonds – – H 2 (hydrogen gas) Biological systems are composed of primarily non-metals (CNOPSH) Non-metals share electrons with each other to complete their valence shells COVALENT balanced, stable. Good building block Non-polar Polar hydrocarbons = C x H x

8. Polar Bonds oxygen has stronger “attraction” for the electrons than hydrogen oxygen has higher electronegativity H H Oxygen Water is a polar molecule + vs – poles + + – – – –

9. Hydrogen Bonding H bonds H O H Between the “negative-ish” oxygen and The ”positive-ish” hydrogen WEAK There is strength in numbers