1. Cellular Chemistry Ch 2

2. Elements of life –Life primarily consists of C, H, O, N –Rest are present in small amounts called trace elements Table 2.1

3. Trace Elements Essential to life Occur in minute amounts common additives to food and water Deficiencies can cause various physiological conditions

4. Subatomic Particles Protons- positive charge Found in the nucleus Neutrons- neutral charge Protons and neutrons occupy the nucleus Electrons- negative charge Arranged in electron shells around the nucleus Figure 2.4A + + –– + – 2 2 2 Protons Neutrons Electrons Mass number = 4 + + 2e – Electron cloud Nucleus

5. Differences in Elements Atoms of each element always have the same number of protons Atomic Number=# protons Mass Number (atomic weight) = Protons + neutrons Atoms have no overall charge, thus… Figure 2.4B + – 6 6 6 Protons Neutrons Electrons Mass # = 12 + + 6e – Nucleus Electron cloud

6. Thus…. Number of protons (+ charge) must be equal to the number of electrons (-) For any element: Number of Protons = Atomic NumberNumber of Protons = Atomic Number Number of Electrons = Number of Protons = Atomic NumberNumber of Electrons = Number of Protons = Atomic Number Number of Neutrons = Mass Number - Atomic NumberNumber of Neutrons = Mass Number - Atomic Number

7. Example KrKrypton Atomic # = 36 Atomic weight = 84 # Protons=? # Neutrons=? # Electrons=?

8. Compounds Chemical elements combine in fixed ratios to form compounds Different combinations of atoms determine the unique properties of each compound Sodium Chlorine Sodium Chloride Figure 2.3

9. Isotopes The number of neutrons in an atom may vary Variant forms of an element are called isotopesVariant forms of an element are called isotopes Some isotopes are radioactiveSome isotopes are radioactive Table 2.4

10. Radioactive isotopes Isotope having an unstable nucleus -nucleus decays emitting particles until stable -Ex: Tritium (hydrogen 3) strontium 90 phosphorus 32 uranium 238

11. Biological Connection Irradiation –A process of disinfestation, pasteurization or sterilization of food products. –Bacterial spores and viruses not inactivated by irradiation –Could still be contaminated by food-service workers after irradiation

12. Biological Connection Research –Radioactive tracers enable researchers to follow particular molecules as they undergo change such as through photosynthesis Medical –Kidney disorders –Medical Imaging PET scansPET scans PET scan image of Parkinson's diseased brain Brown.edu 2008

13. Electrons, Electrons, Electrons! The active part of the atomThe active part of the atom –Only part directly involved in chemical activity Interactions between electrons form chemical bondsInteractions between electrons form chemical bonds Electron shellsElectron shells –Arranged in shells, which may contain different numbers of electrons –Shells are “Full” with either 2 or 8 electrons

14. Electron arrangement determines the chemical properties of an atom –Electrons in an atom are arranged in shells, which may contain different numbers of electrons Hydrogen (H) Atomic number = 1 Electron Carbon (C) Atomic number = 6 Nitrogen (N) Atomic number = 7 Oxygen (O) Atomic number = 8 Outermost electron shell (can hold 8 electrons) First electron shell (can hold 2 electrons) Figure 2.6 Electron Shells

15. Electron shells Valence electron shell –Outermost shell of electrons –These electrons interact with other atoms Hydrogen (H) Atomic number = 1 Electron Carbon (C) Atomic number = 6 Nitrogen (N) Atomic number = 7 Oxygen (O) Atomic number = 8 Outermost electron shell (can hold 8 electrons) First electron shell (can hold 2 electrons) Figure 2.6

16. Electronegativity Atom’s attraction for shared electronsAtom’s attraction for shared electrons –Greater the electronegativity, stronger the pull on e-

17. Covalent Bonds Pairs of e- shared between pairs of atomsPairs of e- shared between pairs of atoms –# of bonds is equal to additional e- necessary to fill the outer shell Polar and Non-polarPolar and Non-polar Covalent bond Diamond with 4 covalent bonds info.lu.farmingdale.edu/.../atomicbonds.html

18. Polarity Non-polar covalent- When the atoms exert a equal pull on the e-Non-polar covalent- When the atoms exert a equal pull on the e- –Overall charge of 0 Polar covalent- when the atoms exert an unequal pull on the e-, bond isPolar covalent- when the atoms exert an unequal pull on the e-, bond is –Overall charge on the more electronegative atom is partially negative and the less electronegative atom is partially positive

19. Polar molecules Unequal e- sharing produces polar bondsUnequal e- sharing produces polar bonds (–) (+) O H H Figure 2.9 Water Molecule

20. Ions Created when an atom gains or looses and electron Results in an net positive or negative charge depending on if the atom gained or lost the e- Anion has neg chrge Cation has positive charge

21. Ionic Bonds Attractions between ions of opposite charge –An electrical attraction between ions with opposite charges results in an ionic bond Transfer of electron Na Sodium atom Cl Chlorine atom Na + Sodium ion Cl – Chloride ion Sodium chloride (NaCl) Na Cl Na + – – – Figure 2.7A

22. NaCl Na has 1 e- in the outer shellNa has 1 e- in the outer shell Cl has 7 e- in the outer shellCl has 7 e- in the outer shell Na “donates” its e- to Cl, leaving Na with only 2 shells and Cl with a full outer shellNa “donates” its e- to Cl, leaving Na with only 2 shells and Cl with a full outer shell

23. NaCl The atom is now an ion –Recall that an ion is an atom or molecule with an electrical charge form either gaining or loosing electrons

24. Hydrogen Bonds Partial + charge allows shared attractions with – charged molecules + charged region always H Hydrogen bond (+) H H (–) O Figure 2.10

25. Water and H bonding 1.H2O is asymmetric 2.Each of the two covalent bonds are highly polarized 3.All three atoms are adept at forming H bonds

26. The importance of hydrogen bonding Cohesion between H 2 0 moleculesCohesion between H 2 0 molecules –Droplet formation –Transportation Adhesion to substrateAdhesion to substrate Surface tensionSurface tension Temperature moderation (body and climatic)Temperature moderation (body and climatic) –When heated, most thermal E is consumed in disrupting the bonds rather than contributing to molecular motion DensityDensity –Ice vs. liquid water

27. Visual representation of a molecule Molecules can be represented in many ways Table 2.8

28. Solvent Water is the solvent of life dissolving any charged or polar substances Solution Aqueous solution Solvent –Dissolving agent Solute –Dissolved substance

29. pH Scale Some molecules disassociate and release H + or OH - –pH is measure of H + ions

30. pH scale A compound that donates H + ions in solution is an acid –Increases the net H + ions in solution A compound that accepts H + ions in solution is a base –Increases the net OH - ions in solution

31. Basic solution Oven cleaner Acidic solution Neutral solution pH scale 0 1 2 3 4 5 6 7 8 9 10 11 12 Lemon juice, gastric juice Grapefruit juice, soft drink Tomato juice Human urine Pure water Human blood Seawater Milk of magnesia Household ammonia Household bleach Increasingly ACIDIC (Higher concentration of H + ) NEUTRAL [H + ]=[OH – ] H+H+ H+H+ H+H+ OH – H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Increasingly BASIC (Lower concentration of H + ) OH – H+H+ 14 13 pH Scale Each unit is 10 fold change in concentration of H + ions Buffers act to minimize Ph changes –React with free H+ of OH ions –Often weak acid/base

32. pH Buffers Maintain pH stability by alternately donating and accepting ions

33. CHEMICAL REACTIONS Chemical reactions change the composition of matter reactants products 2 H 2 O2O2 2 H 2 O Figure 2.17A

34. Videos AtomsAtoms http://www.youtube.com/user/greatpacificmedia# p/u/48/pV822HfqT44http://www.youtube.com/user/greatpacificmedia# p/u/48/pV822HfqT44 Ionic and Covalent bondingIonic and Covalent bonding http://www.youtube.com/watch?v=QqjcCvzWww w http://www.youtube.com/watch?v=QqjcCvzWww w http://www.youtube.com/user/greatpacificmedia# p/u/49/UR4eG60jjQQhttp://www.youtube.com/user/greatpacificmedia# p/u/49/UR4eG60jjQQ Hydrogen Bonding http://www.youtube.com/watch?v=lkl5cbfqFRM& feature=relatedhttp://www.youtube.com/watch?v=lkl5cbfqFRM& feature=related http://www.youtube.com/watch?v=cgiNk94XyaI