1. AP Biology Chapter 2 The Chemical Context of Life 2011-2012

2. AP Biology Why are we studying chemistry? Biology has chemistry at its foundation 2011-2012

3. AP Biology The Basics Everything is made of matter Matter is made of atoms Atoms are made of: protons+mass of 1 nucleus neutrons0mass of 1 nucleus electrons- mass <<1 orbits Different kinds of atoms = elements 2011-2012

4. AP Biology The World of Elements 2011-2012

5. AP Biology Elements of Life The names of the elements are abbreviated. Often, the abbreviation makes perfect sense (C for carbon) and sometimes it does not (Na for sodium). There is an abundance of elements on earth and in living systems (over 100 on the Periodic Table) but

6. AP Biology Life requires ~25 chemical elements About 25 elements are essential for life Four elements make up 96% of living matter: carbon (C) hydrogen (H) carbon (C) hydrogen (H) oxygen (O) nitrogen (N) oxygen (O) nitrogen (N) Four elements make up most of remaining 4%: phosphorus (P) calcium (Ca) phosphorus (P) calcium (Ca) sulfur (S) potassium (K) sulfur (S) potassium (K) 2011-2012

7. AP Biology

8. Models of atoms 2011-2012 (c)

9. AP Biology Atomic structure determines behavior The number of protons in an atom determines the element # of protons = atomic number this also tells you # of electrons All atoms of an element have same chemical properties all behave the same properties don’t change 2005-2006

10. AP Biology Isotopes Different number of neutrons (heavier) Some are unstable nuclear reactions / decay Split off neutrons &/or protons radioactivity Biological tool Biological hazard 2011-2012

11. AP Biology Effect of electrons chemical behavior of an atom depends on its electron arrangement depends on the number of electrons in its outermost shell, the valence shell 2011-2012 Bonding Properties How does this atom behave?

12. AP Biology Effect of electrons chemical behavior of an atom depends on number of electrons in its outermost shell 2011-2012 Bonding Properties How does this atom behave?

13. AP Biology Elements & their valence shells 2011-2012  Elements in the same row have the same number of shells

14. AP Biology Elements & their valence shells 2011-2012  Elements in the same column have the same valence & similar chemical properties

15. AP Biology Elements & their valence shells 2011-2012  Moving from left to right, each element has a sequential addition of electrons (and protons)

16. AP Biology Chemical reactivity Atoms tend to Complete a partially filled outer (valence) electron shell or Empty a partially filled outer (valence) electron shell This tendency drives chemical reactions 2011-2012

17. AP Biology Ionic bonds Ions are produced when atoms can obtain a stable number of electrons by giving up or gaining electrons. For example Na (sodium) can donate an electron to Cl (chlorine) generating Na+ and Cl-. The ion pair is held together by strong electrostatic attractions called ionic bonds 2011-2012

18. AP Biology Covalent bonds Two atoms need an electron Share a pair of electrons Strong bond both atoms holding onto the electrons Forms molecules example: water = takes energy to separate 2011-2012

19. AP Biology Double covalent bonds Two atoms can share more than one pair of electrons double bonds (2 pairs of electrons) triple bonds (3 pairs of electrons) Very strong bonds 2011-2012

20. AP Biology Multiple covalent bonds 1 atom can form covalent bonds with two or more other atoms forms larger molecules ex. carbon 2011-2012

21. AP Biology Polar covalent bonds aka Hydrogen bonding Pair of electrons not shared equally by 2 atoms Water = O + H 2011-2012  oxygen has stronger “attraction” for the shared electrons than hydrogen  oxygen has higher electronegativity

22. AP Biology Polar covalent bonds 2 hydrogens in the water molecule form an angle Water molecule is polar oxygen end is – hydrogen end is + electrostatic attraction Leads to many interesting properties of water…. 2011-2012

23. AP Biology Hydrogen bonds Positive H atom in 1 water molecule is attracted to negative O in another Can occur wherever an -OH exists in a larger molecule Weak bonds 2011-2012 Hydrogen Bonds

24. AP Biology Van der Waals interactions (how geckos walk on the ceiling ) very weak, transient connections that are the result of asymmetrical distribution of electrons within a molecule

25. AP Biology

26. Bonding by Analogy: Dog - Bone Bonds

27. AP Biology Ionic Bonds: One big greedy thief dog! Ionic bonding can be best imagined as one big greedy dog steeling the other dog's bone. If the bone represents the electron that is up for grabs, then when the big dog gains an electron he becomes negatively charged and the little dog who lost the electron becomes positively charged.

28. AP Biology Covalent Bonds: Dogs of equal strength. Covalent bonds can be thought of as two or more dogs with equal attraction to the bones. Since the dogs (atoms) are identical, then the dogs share the pairs of available bones evenly. Since one dog does not have more of the bone than the other dog, the charge is evenly distributed among both dogs. The bond is not “polar” because the dogs share equally.

29. AP Biology Polar Covalent Bonds: Unevenly matched but willing to share. These bonds can be thought of as two or more dogs that have different desire for bones. The bigger dog has more strength to possess a larger portion of the bones. Sharing still takes place but is an uneven sharing. In the case of the atoms, the electrons spend more time on the end of the molecule near the atom with the greater electronegativity (desire for the electron) making it seem more negative and the other end of the molecule seem more positive.

30. AP Biology Reductionist view of biology Matter is made of atoms Life requires ~25 chemical elements Atomic structure determines behavior of an element Atoms combine by chemical bonding to form molecules Weak chemical bonds play important roles in chemistry of life A molecule’s biological function is related to its shape Chemical reactions make & break chemical bonds 2011-2012

31. AP Biology Any Questions?? 2011-2012