1. The Chemical Context of Life
Campbell and Reece
Chapter 2
The Chemical Context of Life

2. Elements & Compounds
Element: substance that cannot be broken down to other substances by chemical reactions
92 natural-occurring elements

4. Compounds 2 or more different elements combined in a fixed proportion
compound has different properties than properties of individual elements that make up the compound

5. Compounds are pure substances

6. Essential Elements of life
those of the 92 that organisms must have to live & reproduce
species specific;
humans need 25 elements
plants need 17

7. Essential elements 96% of living matter (by mass) made up of: Oxygen
Carbon
Hydrogen
Nitrogen

8. 4% of living matter (by mass) made up of:
Calcium
Phosphorus
Potassium
Sulfur
Chlorine
Magnesium

9. Trace Elements make up <1%
organisms require these in minute amounts
to name only a few:
Iron
Iodine (in vertebrates only)
Zinc
Selenium
Manganese

10. Toxic elements
Arsenic:
Mercury

12. Properties of elements

13. Atomic mass 1 proton or 1 neutron = 1 amu
1 amu = 1.7 x 10² g = 1 dalton
mass of e- ignored

14. Mass number
#protons + #neutrons

15. isotopes different forms of same element: same # protons
different # of neutrons
occurs naturally
Atomic Mass see on periodic table is weighted mass average of all isotopes

16. Radioactive Isotopes nucleus spontaneously decays
giving off particles & energy
used medically to measure an organ’s function, monitor tumor growth

17. Radioactive isotopes
decay hazardous to living organisms by damaging cellular molecules

18. Energy levels of electrons
electrons only subatomic particle involved in chemical reactions
e- have PE due to their position around nucleus of atom
electron’s (-) charge attracted to (+) proton
the farther out e- is from nucleus, the more PE that e- has

19. Electron energy levels

20. Valence electrons electrons in outermost shell
if valence shell completely filled: atom is nonreactive (inert like noble gases)

21. Electron orbitals

23. Chemical bonds
formed by interactions between atoms with incomplete valence orbitals

24. Covalent bonds sharing of a pair of valence electrons by 2 atoms
2 or more atoms held together by covalent bonds = molecule

25. Types of covalent bonds
1 pair e- shared = single covalent bond
2 pair e- shared = double covalent bond
3 pair e- shared = triple covalent bond
hydrogen gas

26. Nonpolar covalent bond
shared pair of electron are shared evenly between the 2 atoms

27. electronegativity
attraction of a particular atom for the electrons in covalent bond
greater the electronegativity on 1 atom over the other in the covalent bond, the more likely the bond will be a polar covalent bond

28. Polar covalent bonds electrons of the bond are not shared equally
bonds vary in their polarity: depends on the relative electronegativity of the 2 atoms

29. Ionic bonds transfer of e- from metal  nonmetal
creates cations (+) & anions (-)
opposite charges attract forming ionic bond
compounds formed by ionic bonds called ionic compounds or salts
as solids form crystals, very strong bonds
as liquids completely dissociate

30. Weak chemical bonds
in living organisms: most of the strongest chemical bonds are covalent
weak bonds also important:
hydrogen bonds, van der Waals, ionic bonds in water
maintain shape of proteins, DNA
reversibility key to their importance

31. Hydrogen bonds water: H held to O in polar covalent bonds
partial (+) charge on H makes it attract the partial (-) charge on O from another water molecule

32. Van der Waals forces
nonpolar covalent bonds may not have electrons symmetrically distributed
@ any given instant in time a region of the molecule may be slightly (-) or (+)  ever-changing regions of (+) or (-) charge
occurs only when atoms or molecules are very close together

33. Molecular shape & function
shape of a molecule key to its function in cell
shape of a molecule with >2 atoms determined by positions of atom’s orbitals

34. Molecular shape
determines how biological molecules recognize & respond to each other with specificity
2 molecules temporarily forming weak bond can only happen if their shapes are complimentary to each other

35. Molecular shape
because morphine and endorphins have same shape that fits into endorphin receptors morphine is able to create same response as endorphins: pain relief & euphoria during stress

36. Endorphins & morphine

38. Chemical reactions
chemical bonds of reactants broken, chemical bonds of products formed in a chemical reaction

39. Chemical equilibrium