The Chemical Basis of Life

• Matter


  • Composition of all living and non living things
  • Anything that occupies space and has mass
• Mass


  Amount of matter in an object
• Weight


  Gravitational force acting on an object of a given mass
• Kilogram


  • International unit for mass
  • Platinum-iridium cylinder
• Gram


  1/1000 the mass of a kilogram
• Element


  Simplest type of matter
• 96% of the body's weight results from the elements oxygen, carbon, hydrogen, and nitrogen
• Atom


  Smallest particle of an element
• Atomic Structure


  • Nucleus - center of an atom
  • Neutron - no electrical charge
  • Proton - one positive charge
  • Electron cloud - region where electrons are most likely to be found
  • Electron - one negative charge
• Atomic number


  Number of protons
• Mass number


  Number of protons + neutrons
• Isotopes


  Same atomic number but different mass numbers
• Atomic mass


  Average mass of its naturally occurring isotopes
• Dalton


  Unified atomic mass unit: 1/12 the mass of 12C
• Avogadro's number


  6.022 x 10^23 - 1 mole
• Molar mass


  1 mol expressed in mass
• Chemical bonds


  Formed when atoms interact to form molecules
• Electron shells


  • Energy levels often depicted as concentric rings
  • Outermost shell (valence shell) determines atom's chemical nature
• Inert


  Does not form chemical bonds with other atoms, valence shell is full
• Chemically reactive


  Valence shell is not full
• Octet rule


  Tendency of atoms to combine with other atoms until each has 8 electrons (2 for hydrogen) in its valence shell
• Electronegativity


  Ability of an atom's nucleus to attract electrons, stronger if there are no or less missing electrons
• Ionic bonds


  Transfer of electrons between atoms
• Ion


  Formed when numbers of protons and electrons are no longer equal
• Cation


  Positively charged ions
• Anion


  Negatively charged ions
• Electrolytes


  Cation and anion that dissociate in water
• Nonelectrolytes


  Molecules that do not dissociate, solutions that do not conduct electricity
• Covalent bonds


  Sharing of electrons between atoms
• Single covalent bond


  Sharing of one pair of electrons by two atoms
• Double covalent bond


  Two atoms share 4 electrons
• Nonpolar covalent bonds


  Equal sharing of electrons
• Polar covalent bonds


  Unequal sharing of electrons
• Molecule


  Two or more atoms chemically combined to form a structure that behaves as an independent unit
• Compound


  Chemical combination of two or more different types of atoms
• The properties of elements can change when they are combined to form compounds
• Molecular mass


  Determined by adding up the atomic masses of its atoms
• Solubility


  Ability of a substance to dissolve in another
• Dissociate


  When ionic compounds dissolve in water and separate from one another
• Energy


  Capacity to do work, move matter