1. CHAPTER 2 The Chemical Context of Life

2. 2.1 Matter is made of elements and compounds.  Organisms are composed of matter - anything that takes up space or has mass  An element is a substance that cannot be broken down by chemical reactions.  Fe, Ca, K  A compound is a substance consisting of two or more elements in a fixed ratio.  NaCl, HCl, H 2 O 2, C 6 H 12 O 6

3. Matter - elements and compounds  Life requires about 25 elements  C, O, H, and N make up 96% of all living matter  S, P, Ca, and K make up the remaining 4%  Trace elements are those that are required, but only small amounts.  N and I Deficits may have severe consequences

4. Nitrogen deficiency - growth of plant Iodine deficiency – enlargement of thyroid gland

5. Table 2.1

6. 2.2 – An element’s properties depend on its structure  An atom is the smallest unit of matter that still retains the properties of an element.  Similar to a cell being the basic unit of life  Subatomic particles help us to better understand atoms.  Protons ( p + )  Neutrons ( n 0 - no charge)  Electrons ( e - )

7. 2.2 Properties and Structure  Atomic number is the # of p +  In neutral (uncharged atom) also equals e -  Mass number (Atomic mass) = p + + n 0  Isotopes are the different forms of an element.  # of n 0 varies in the nucleus  Often used as radioactive markers/tracers for tests You should be able to identify and determine mass and atomic number for elements on the p-table.

8. 2.2 – Properties and Structure  The e - of an atom have different energy – ability to do work.  e - have stored (potential)energy because of their position in relation to the nucleus.  1 st shell (closest to nucleus) least energy  2 nd shell more energy than 1 st, etc.  Outer most shell contains valance e -  identified by group number (groups ↑↓)  # of unpaired e - indicates reactivity of element

9. Third shell (highest energy level) Second shell (higher energy level) Energy absorbed First shell (lowest energy level) Atomic nucleus Energy lost e - Energy Shells

10. Valence e - of common elements Hydrogen 1 H Lithium 3 Li Beryllium 4 Be Boron 5 B Carbon 6 C Nitrogen 7 N Oxygen 8 O Fluorine 9 F Neon 10 Ne Helium 2 He Atomic number Element symbol Electron- distribution diagram Atomic mass 2 He 4.00 First shell Second shell Third shell Sodium 11 Na Magnesium 12 Mg Aluminum 13 Al Silicon 14 Si Phosphorus 15 P Sulfur 16 S Chlorine 17 Cl Argon 18 Ar

11. 2.3 Chemical Bonding  Atoms will bond with other atoms to gain stability.  Stable when valence shell is full. Covalent bonds Ionic bonds

12. Chemical Bonding  Covalent bonds are formed when 2 atoms share a pair or pairs of valence e-.  Hydrogen (H) atoms will share their e-. They become H-H.  H 2 O – H covalently bonded to O More on this in Ch.3

13. 2.3

14. 2.3 – Chemical Bonding  Electronegativity is a measure of an atoms ability to the attract the e- of another atom to form a covalent bond.  Sharing of e- results in a strong bond.  Two types of covalent bonds Nonpolar Polar

15. Covalent bonding…  Nonpolar when the e- are shared equally  results in no charge on either atom involved  Polar when one atom is bonded to a more electronegative atom  results in charge (+/-) on one atom

16.  – – ++ ++ H H O H2OH2O Polarity of H 2 O

17. 2.3 Chemical Bonding  Ionic bonds occur when two atoms are so unequal in their attraction for e - that one atom will strip the e - from its partner.  These bonds are not as strong as covalent bonds.  An ion is a charged atom;  Cations have a “+” charge, ca+ion  Anions have a “–” charge, a negative ion  Compounds formed by ionic bonds are salts.

18. Ionic Bonds NaCl Na Cl Na Sodium atom Chlorine atom Cl Na + Sodium ion (a cation) Cl – Chloride ion (an anion) Sodium chloride (NaCl)

19. 2.3 Chemical Bonding  The advantage of weak bonding is that the contact/bond between atoms can be brief.  Hydrogen bonds occur when H is covalently bonded to an electronegative atom and attracted to another electronegative atom.  Water and ammonia  Water and water  Bases in DNA

20. Hydrogen Bonding   ++ ++    ++ ++ ++ Water (H 2 O) Ammonia (NH 3 ) Hydrogen bond

21. Hydrogen bonding…

23. Shape and Function  Molecules have distinct shape and size  Related to atoms and bonds contained within  As mentioned before shape/structure is directly related to function  Determines how molecules interact and respond to each other Opiates and endorphins – chemicals with similar shapes interact with similar receptors on the brain, causing similar effects

24. 2.4 – Reactions make or break bonds.  Chemical reactions involve breaking and making new chemical bonds.  Start with reactants.  End with products. Coefficient and subscript tells you how much of each  What is the reverse reaction of photosynthesis?

25. Chemical Reactions

26. 2.4 – Reactions make or break bonds.  Chemical equilibrium occurs when the forward and reverse reactions occur at the same rate.  Concentrations have stabilized  Concentrations are NOT equal each other