1. Essential Chemistry for Biology Chapter 2

2. Tracing Life Down to the Chemical Level

3. Basic Chemistry  Matter Anything that takes up space and has mass Can exist as a liquid, solid, or gas  Elements Basic building block of matter 92 naturally occurring elements

4. Basic Chemistry  Only 6 elements that make up most of the body weight of organisms CCarbon HHydrogen NNitrogen OOxygen PPhosphorus SSulfur

5. Trace Elements Trace elements make up 0.01% of human body weight, but still very important

6. Each Element Consists of ONE Kind of Atom  Smallest unit that retains the properties of a given element And to enter a chemical reaction  Composed of subatomic particles: Protons (p+) Neutrons Electrons (e-)  Move @ atomic nucleus  Usually (e-) = (p+) Electrically neutral

7. Atomic Symbol Atomic Mass = Number of Protons + Number of Neutrons Atomic Number = The Number of Protons in the Nucleus

8. Valence Shell

9. Molecules and Compounds  Molecules Chemical bonding that joins atoms Some contain atoms of only one element  N 2  Compounds Atoms of two or more different elements  H 2 O  Mixture Two or more molecules mingling together

10. Chemical Bonds  Atoms are held together by bonds  3 main types: Ionic bond  Accept or donate electrons Covalent bond  Share one or more electrons Hydrogen bond

11. Ionic Bond  Atoms gain and lose electrons Balance between protons and electrons shifts Become “ionized”  Ion Atom that has a charge Losing an electron results in a net positive Gaining an electron results in a net negative charge  Ionic bond Association of two ions that have opposing charges

12. Which will form an ionic bond? Potassium (K) Chlorine (Cl) Helium (He) Argon (Ar)

13. Can Mg and Cl form an ionic bond? Magnesium (Mg) Chlorine (Cl)

14. Covalent Bond  Covalent bond Stable and stronger than ionic bonds Atoms share electrons  Each atom will have a completed outer shell  Bond Notation Single covalent bonds are written as H-H Double covalent bonds are written as O=O

15. A covalent bond can be nonpolar or polar  Nonpolar covalent bond Sharing of electrons between atoms is fairly equal  Polar covalent bond Unequal sharing of electrons

16. Hydrogen Bond  Hydrogen bond Weak attraction  Form and break easily Occurs between polar molecules  Polar bonds have charges on either end and often attract to each other

17. Chemical Reactions  Cells constantly rearrange molecules by breaking existing chemical bonds and forming new ones  Reactants Starting materials  Products End materials  Chemical reactions cannot create or destroy matter, They only rearrange it

19. Solvent of life  Water dissolves other polar substances Solvent  Ions and polar molecules easily dissolve in it Solute  A dissolved substance Hydrophilic  water-loving molecules  form hydrogen bonds with water Hydrophobic  water-fearing molecules  do not form hydrogen bonds with water

20. Acids and Bases  When water ionizes, it releases an equal number of hydrogen ions (H + ) and hydroxide ions (OH - )  Some substances release more or fewer or each Acids - Excess hydrogen ions Bases - Excess hydroxide ions

21. Acidic and Basic Solutions  Acidic Solutions Sharp, sour taste Molecules that dissociate in water  Release hydrogen ions (H+)  Basic Solutions Bitter taste Molecules that either take up hydrogen ions (H+) or release hydroxide ions (OH-)

22. pH Scale  The pH Scale Ranges from 0 - 14 pH below 7 is acidic [H + ] > [OH - ] pH above 7 is alkaline [OH - ] > [H + ] pH of 7 is neutral [H + ] = [OH - ]  Buffer Chemical or combination of chemicals that keeps pH within normal limits