1. Matter takes up space and has mass Everything composed of matter Any biological process, function or structure can be broken down to its chemical level -> molecules/atoms

2. Atoms and Molecules Element-substance that cannot be broken down chemically to simpler substances with different properties There are 92 naturally occurring elements, 25 of which are essential to life l O - 65% l C - 18.5 % l H - 9.5 % l N - 3.3 %

3. C, H, O found in carbs, proteins, lipids and nucleic acids N found in proteins, nucleic acids P found in nucleic acids S

4. Ca, P, K, S, Na, Cl, Mg = ~4 % Few elements exist pure (alone) in nature - they are part of compounds Compounds-substance containing two or more elements in a fixed ratio

5. Atomic structure Protons and neutrons located in the nucleus at the center of the atom Electrons found outside nucleus in orbitals, electron shells, or energy levels

6. Atomic number - the # of protons in an element, gives it its unique properties - all atoms of a particular element have the same # of protons Atomic mass =

7. Atomic Symbols E ach element represented by unique atomic symbol lOlOne or two letters lFlFirst letter capitalized lSlSuperscripted number before: Represents mass number lSlSubscripted number before Represents to atomic number Number of protons in nucleus Mass Number Atomic Number Atomic Symbol 12 6 Carbon C

8. Periodic Table E lements grouped in periodic table based on characteristics lHlHorizontal rows = periods; larger and larger 1 H 1.008 3 Li 6.941 11 Na 22.99 19 K 39.10 4 Be 9.012 12 Mg 24.31 20 Ca 40.08 5 B 10.81 13 Al 26.98 21 Ga 69.72 6 C 12.01 14 Si 28.09 22 Ge 72.59 7 N 14.01 15 P 30.97 23 As 74.92 8 O 16.00 16 S 32.07 24 Se 78.96 9 F 19.00 17 Cl 35.45 25 Br 79.90 10 Ne 20.18 18 Ar 39.95 26 Kr 83.60 2 He 4.003 I IIIIIIV VVIVII VIII 1 2 3 4 Groups Periods

9. Isotopes Isotope - same # of protons (same element), different # of neutrons (different atomic mass) Radioactive isotopes (radioisotopes) -

10. Radioisotopes Tracers-monitor fate of atoms Useful in medical diagnosis (PETscans) Exposure to high levels can damage molecules (DNA) harming organisms and causing cancer

11. Electrons and Bonding Electrons determine how atoms behave when contacting other atoms-this is the single most important factor in the chemistry of living things The # of electrons in the outermost shell (valence) determines chemical properties of atoms Atoms with incomplete outer shells tend to interact with other atoms

12. Atoms want to have their outermost energy level filled They can fill it by sharing electrons, or by giving electrons to or receiving electrons from another atom

13. Compounds and Molecules When atoms of two or more elements chemically bond together, a compound is formed

14. The shapes of molecules are important in the structural and functional roles they play in living things

15. Chemical Bonds Sharing of electrons forms a covalent bond Giving and receiving electrons form ionic bonds

16. Covalent bond between atoms form molecules

17. Ionic bond One atom (Na) gives (donates) an electron The other atom (Cl) receives an electron

18. The atom that gives up an electron becomes a positive ion The atom that receives an electron becomes a negative ion Opposite charges attract each other (electrostatic attraction) to form am an ionic bond

19. Electrons and energy levels Excited state - when an electron absorbs additional energy to move up to the next energy level. Electrons return to original ground state by emitting extra energy Plants use this brief energy increase (10 -8 sec) during photosynthesis

20. Biologically Important Weak Bonds Organisms need to be able to change to maintain homeostasis (chemical balance) to meet changing environment Covalent bonds are too strong and cannot be broken easily and changed Weak bonds of biological importance include: ionic bonds, hydrogen bonds, van der Waals interactions

21. Hydrogen Bonds Electrostatic attraction between oppositely charged portions of nearby molecules Hydrogen bonds form between molecules that have no net overall electrical charge (are neutral) Ionic bonds form between oppositely charge atoms

22. Weak bonds play crucial role in stabilizing shape of large molecules like DNA, proteins Covalent bonds = 50-110 kcal/mole Ionic bonds = 10 kcal/mole Hydrogen bonds = 4-5 kcal/mole van der Walls = 1-2 kcal/mole