The Chemical Context of Life

1
Chapter 2

• The Chemical Context of Life

2

• Matter
• Element
• -92 naturally occurring, 12 more man
• made
• -symbol is Latin derived
• Compound
• -ex NaCl
• Essential elements to living things 25 of the
  92
• 96 made of C, O, H, N
• 4 P, S, Ca, K, a few others
• Trace elements

3

• Atoms
• electrons 1/2000 of proton/neutron
• (e-)
• atomic number
• number of protons (p)
• number of electrons (e-)
• 2He
• mass number
• protons neutrons (n0)
• (nucleus)
• 4He
• 2

4

• Isotope
• atoms w/ same of protons, but different
• number of neutrons
• ex 14C 12C 13C
• radioactive, unstable dont have
  tendency to lose particles stable
• Half life
• time it takes 50 of radioactive atoms to
• decay

5
What are radioactive isotopes used for?

• biological tracers
• fossil dating
• diagnostic tools in medicine

6

• Electrons
• potential energy due to position/relation
• to nucleus
• Energy levels (electron shells)
• different states of potential energy
• farther out absorb energy
• farther in lose energy
• Orbital
• 3D space where electron is found 90 of time
• 1s 2e-
• 2s 8e- 2n2
• 2px 2e-
• 2py 2e- 8e-
• 2pz 2e-

7

• Valence electrons
• determine chemical properties
• Octet rule
• valence shell complete with 8 electrons
• Inert

8

• Bonding
• molecule
• 2 or more atoms held together
• by chemical bonds
• ex O2 NaCl O3

9

• Covalent
• ex H2
• H-H OO N N
• valence
• bonding capacity
• electronegativity
• attraction of an atom for the electrons
• of a covalent bond
• nonpolar
• atoms are equally electroegative electrons
• shared equally ex CH4
• polar one is more electronegative not
  shared equally
• ex H2O

10

• Ionic
• loss/gain of e- due to electronegativity
• ex NaCl
• ion
• -electrically charged atom
• may also be groups of atoms (NH4)
• other salts are also ionic
• -break easily in water
• cation anion

11
Other weak bonds

• H bonds (IMF)
• -in covalent molecules attracted to each other
• and N or O, as in water
• van der Waals interactions
• -ever changing hot spots of or charges
• that enable all molecules atoms to stick
• together due to chance accumulation of e-

12

• 5) Hydrophobic interactions
• water fearing
• -coalesce in water to minimize exposure
• -once close together, van der Waals
• reinforces interaction

13
Chemical reactions

• -make/break bonds
• Mg 2Cl MgCl2
• reactants products
• 3H2 N2 2NH3
• (reversible reaction)
• chemical equilibrium eventually reached when
  reactions offset one another (concentrations have
• stabilized) not in equal concentration