CHAPTER 2 The Chemistry of Living Things

All Matter Consists of Elements Made of Atoms Atoms, the smallest functional unit, consist of: Protons: positive charge, have mass Neutrons: no charge, have mass Electrons: negative charge, have no discernable mass Slide 2.1

Isotopes Radioisotopes Same element, same atomic number = same number of protons and electrons Different number of neutrons = different weight Radioisotopes Are unstable (varies with isotope) ex.: I131 used in the treatment of Grave’s Disease Emit energy (radiation) Emit particles Slide 2.2

Atoms Combine to Form Molecules Joining atoms requires energy Energy is the capacity to do work Stored energy = potential energy Energy in motion, doing work = kinetic energy Electrons have potential energy Shells = the energy levels of electrons Orbitals describe the probable location of an electron . Slide 2.3

Three Types of Chemical Bonds Table 2.1 Slide 2.4

Ionic Bonds Written NaCl NOT Na-Cl

Elements of Living Organisms Table 2.2 Slide 2.5

Life Depends on Water Water molecules are polar (they have slight electrical charges) Water is liquid at body temperature Water can absorb and hold heat energy Slide 2.6

Two Important Biological Functions of Water Water is the biological solvent Water helps regulate body temperature Has high heat of evaporation Slide 2.7

Hydrogen bonds (dotted lines) Oxygen slightly –ve charge Hydrogen slightly +ve

Water Keeps Ions in Solution Figure 2.8 Slide 2.8

The Importance of Hydrogen Ions Acids are proton (hydrogen ion) donors, bases accept hydrogen ions pH Scale = a logarithmic scale of the hydrogen ion concentration (going from a pH of 2 to 4 is a change of 2 numbers= 102, so pH 4 is 100 times less acidic than pH 2 Buffers: minimize pH change Carbonic acid and bicarbonate act as one of body’s most important buffer pairs Slide 2.9

The pH Scale Figure 2.10 Slide 2.10

The Organic Molecules of Living Organisms Carbon, the building block of living things: Comprises 18% of body by weight Forms four covalent bonds Can form single or double bonds Can build micro- or macromolecules Slide 2.11