1. Chapter 2: Atoms and Molecules of Ancient Earth Life requires about 25 elements carbon (C) oxygen (O) hydrogen (H) nitrogen (N)

2. Chapter 2: Atoms and Molecules of Ancient Earth Atoms and molecules: *Atomic number *Atomic weight The energy levels of electrons: *electrons vary in energy Energy Potential energy 4 2 23 11 1 1 He Na H

3. Atoms with full shells are chemically stable, and won’t react easily with other atoms.

4. Chapter 2: Atoms and Molecules of Ancient Earth Electron configuration and chemical properties: *chemical behavior due to electrons

5. ElementSymbolAtomic Number # Electrons normally gained (+) or lost (-) AluminumAl13-3 ArgonAr180 BerylliumBe4-2 BoronB5-3 CarbonC6+ or – 4 ChlorineCl17+1 FluorineF9+1 HeliumHe20 HydrogenH1 LithiumLi3 MagnesiumMg12-2 NeonNe100 NitrogenN7+3 OxygenO8+2 PhosphorusP15+3 SiliconSi14+ or – 4 SodiumNa11 SulfurS16+2 Recall: Atomic Number is the number of protons found in nucleus.

6. Atoms combine by chemical bonding to form molecules *Chemical behavior depends on valence electrons *Covalent bond Examples: Covalent bond Double Covalent bond Chapter 2: Atoms and Molecules of Ancient Earth

7. Atoms combine by chemical bonding to form molecules: Another example: Compound *electronegativity nonpolar covalent bond polar covalent bond Example: H 2 O - water Chapter 2: Atoms and Molecules of Ancient Earth

8. H + Li + Na + K + Positive ions are missing electrons, and therefore have a positive charge (H + Li + Na + K + ) F - Cl - Br - I - Negative ions have extra electrons, thus a negative charge (F - Cl - Br - I - ) Ions - Atoms in which number of electrons does not equal number of protons.

9. Atoms combine by chemical bonding to form molecules: *ionic bonds 11 17 *ion *cation *anion ionic compounds or salts Chapter 2: Atoms and Molecules of Ancient Earth

10. Covalent vs. ionic bond - draw

11. Atoms combine by chemical bonding to form molecules: *bonding between molecules Hydrogen bonds: Chapter 2: Atoms and Molecules of Ancient Earth

12. Polarity of water: Water: what’s the big deal? *Hydrogen bonding water transport in plants adhesion *Cohesion Chapter 2: Atoms and Molecules of Ancient Earth

13. Water is the solvent of life *solution *solvent *solute *aqueous solution *polar and ionic molecules can be dissolved in water

14. Chapter 2: Chemical Components of Cells Hydrophilic and hydrophobic substances *hydrophilic *hydrophobic

15. Chapter 2: Chemical Components of Cells Hydrophilic and hydrophobic substances *hydrophilic *hydrophobic The dissociation of water molecules H 2 O H + + OH - Acids and bases *acid *base

16. Chapter 2: Chemical Components of Cells The pH scale