1. Chapter 2 Atoms, Molecules, and Life

2. Chapter 2 2 Covalent bond — electrons shared Shared unequally — polar Shared unequally — polar Shared equally — nonpolar Shared equally — nonpolar Ionic bond — electron transfers total # Both atoms ionized Both atoms ionized May dissociate in water May dissociate in water Chemical Bonding

3. Chapter 2 3 Bonding Involves Electrons One pair electrons per bond Outer electrons form bonds Behave using “octet rule” If nearly eight in outer shell Desires more electrons Desires more electrons Oxidizer Oxidizer If less than four in outer shell Desires fewer electrons Desires fewer electrons Reducer Reducer

4. Chapter 2 4 ƒ2-4a&b Most Elements Molecular (a) In hydrogen gas, one electron from each hydrogen atom is shared, forming a single covalent bond. The resulting molecule of hydrogen gas is represented as H–H or H 2. (b) In oxygen gas, two oxygen atoms share four electrons, forming a double bond (O=O or O 2 ).

5. Chapter 2 5 ƒ2-3a,b ± + – ± + ±+ ± +± + ± + ± + ± + – – –– – – ± + – – – ± + – ± + ±+ ± +± + ± + ± + ± + – – –– – – ± + – – – – – – – – – – Ionic Bonding in NaCl ± + – ± + ±+ ± +± + ± + ± + ± + – – –– – – ± + – – –– Sodium #e=2+8+1=#p ± + – ± + ±+ ± +± + ± + ± + ± + – – –– – – ± + – – – ––– – – – – Chlorine #e=2+8+7=#p – – Sodium ion #e=#p-1 Chlorine ion #e=#p+1 – Electron Completely Transferred Negative charge Positive charge

6. Chapter 2 6 ƒ2-3c Ionic Bonding in NaCl Cl - Na + Opposites attract. Sodiums nestle between chlorines. Perfectly cubical crystals. Cl - Na +

7. Chapter 2 7 ƒ2-4c Water Is Covalent Electron pair forms covalent bond Each spends some time w/one, then the other atom Less time w/H, more time w/O Causes polarity of H 2 O molecule

8. Chapter 2 8 ƒ2-4c Water Molecule H 2 O HH O Oxygen Hydrogens

9. Chapter 2 9 Polar vs. Nonpolar Bonds Distribution of charge on molecule Polar — charged surface Prefer other charged molecules Prefer other charged molecules Soluble in water Soluble in water Nonpolar — no residual charge Prefer uncharged molecules Prefer uncharged molecules Soluble in oils Soluble in oils

10. Chapter 2 10 T2-3 Bonding Patterns of Common Atoms Sulfur Phosphorus Oxygen Nitrogen Carbon Hydrogen

11. Chapter 2 11 Free Radicals Some cellular reactions produce free radicals Free radical : a molecule whose atoms have one or more unpaired electrons in their outer shellsFree radical : a molecule whose atoms have one or more unpaired electrons in their outer shells Free radicals are highly unstable and reactive Free radicals steal electrons, destroying other molecules Free radicals steal electrons, destroying other molecules Cell death can occur from free radical attack Cell death can occur from free radical attack

12. Chapter 2 12 Free Radicals Free radicals are involved in causing heart disease, Alzheimer’s, cancer, and aging Antioxidants like vitamins C and E render free radicals harmless

13. Chapter 2 13 ƒ2-5 Hydrogen Bonds O O H H H H + + + – – + + Water molecules carry slight charges Electrons favor O over H Water molecules carry slight charges Electrons favor O over H Hydrogen bonds form between O of one and H of another Hydrogen bonds form between Oof one and Hof another Not a “REAL” bond!!! No transfer of electrons! Not a “REAL” bond!!! No transfer of electrons!

14. Chapter 2 14 Hydrogen Bonds Hydrogen Bonds Hydrogen bonds are like two children holding very-slippery hands. The bonds constantly break and reform Hydrogen bonds are like two children holding very-slippery hands. The bonds constantly break and reform

15. Chapter 2 15 ƒ2-6 NaCl Dissolved by Water NaCl is ionicly bonded NaCl is ionicly bonded Water is polar and charged Water is polar and charged O sticks to Na + O sticks to Na + H sticks to Cl - H sticks to Cl -

16. Chapter 2 16 2-7Dissociation+ WaterWater– Hydroxide ion + Hydrogen ion A few water molecules naturally dissociate Hydroxide ion is negative and basic Hydroxide ion is negative and basic Hydroxide Hydroxide ion ion is negative and basic Hydrogen ion is positive and acidic Hydrogen ion is positive and acidic Hydrogen Hydrogen ion ion is positive and acidic Makes water a good solvent Makes water a good solvent H2OH2OH2OH2O Hydrogen Bond Glucose H2OH2OH2OH2O H2OH2OH2OH2O H2OH2OH2OH2O H2OH2OH2OH2O

17. Chapter 2 17 ƒ2-8 Cohesion among Water Molecules

18. Chapter 2 18 ƒ2-9 The pH Scale Neutral pH + = pOH – Increasingly Acidic pH + > pOH – Increasingly Basic pH + < pOH – 0 0 -1 -2 -2 -3 -3 -4 -4 -5 -5 -6 -6 -7 -7 -8 -8 -9 -9 -10 -10 -11 -11 -12 -12 -13 -13 -14 -14 Lemon Juice Lime Juice Stomach Acid Coffee Urine Water Blood Sea Water Baking Soda Bleach Ammonia Oven Cleaner

19. Chapter 2 19 Water Stabilizes Temperature Very low or very high temperatures may damage enzymes or slow down important chemical reactions Water moderates the effect of temperature change Temperature reflects the speed of molecular motion Temperature reflects the speed of molecular motion It requires 1 calorie of energy to raise the temperature of 1g of water 1 o C (the specific heat of water), so it heats up very slowly It requires 1 calorie of energy to raise the temperature of 1g of water 1 o C (the specific heat of water), so it heats up very slowly

20. Chapter 2 20 Water Stabilizes Temperature Water requires a lot of energy to turn from liquid into a gas ( heat of vaporization ) Evaporating water uses up heat from its surroundings, cooling the nearby environment (as occurs during sweating) Evaporating water uses up heat from its surroundings, cooling the nearby environment (as occurs during sweating) Because the human body is mostly water, a sunbather can absorb a lot of heat energy without sending her/his body temperature soaring

21. Chapter 2 21

22. Chapter 2 22 Water Stabilizes Temperature Water requires a lot of energy to be withdrawn in order to freeze ( heat of fusion ) Water freezes more slowly than other liquids Most substances become denser when they solidify from a liquid Ice is unusual because it is less dense than liquid water

23. Chapter 2 23 Water molecules spread apart slightly during the freezing process

24. Chapter 2 24

25. Chapter 2 25 Water Forms an Unusual Solid Ice floats in liquid water Ponds and lakes freeze from the top down and never freeze completely to the bottom Many plants and fish therefore are not frozen Many plants and fish therefore are not frozen

26. Chapter 2 The End