1. The Chemistry of Life Biology: Chapter Two

2. Atoms An atom is the smallest unit of matter that cannot be broken down by chemical means Consists of 3 particles – electrons (- charge) – Protons (+ charge) – Neutrons (no charge)

3. Elements Elements are pure substances made of only one kind of atom; there are over 100 known elements Elements differ in the number of PROTONS their atoms contain

4. Isotopes Atoms of an element that contain different numbers of neutrons are called isotopes. – EX: isotopes of Carbon = carbon-12, carbon-13, carbon-14 Each contain 6 protons but different neutrons

5. Periodic table, pages 1046, 1047

6. Compounds A compound is a substance made of the joined atoms of two or more different elements. Ex: NaCl, sodium chloride H 2 O, water NH 3, ammonia

7. Covalent Bonds Covalent bonds form when two or more atoms share electrons to form a molecule Example = H 2 O, water

8. Hydrogen Bonds A hydrogen bond is a weak chemical attraction between polar molecules Polar molecule = a molecule that has opposite charges (polarity) (+/-)

9. Hydrogen Bonding in Water Molecules

10. Ions and Ionic Bonds An atom that has gained or lost electrons is called an ion. Ions of opposite charge (+/-) may interact to form a ionic bond. Ex: NaCl (sodium chloride)

11. Water and Solutions Fun Facts: – Water makes up 70% of your body! – 2/3 of the molecules in your body are H 2 O molecules – Most cellular events take place in H 2 O – Water absorbs heat more slowly and retains this energy longer! (compared to other liquids)

12. Cohesion = attraction between substances of the SAME kind

13. Adhesion = attraction between DIFFERENT substances

14. Acids and Bases While the bonds in water molecules are strong, at any given time a tiny fraction of those bonds might break, forming a hydrogen ion, H +, and a hydroxide ion, OH - H 2 O  H + + OH -

15. Acid = form hydrogen ions when dissolved in water Base = form hydroxide ions AcidicNeutralBasic