Chapter 2 Atoms and Molecules: by 52u2QI8A

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									CHAPTER 2 ATOMS AND
MOLECULES:
The Chemical basis of life.
CHEMICALS
 Non-living building blocks of living things.
 Provide communication – pheromones, hormones,
  neurotransmitters.
 Provide energy.

 Compose our atmosphere.

 Love!
SUMMARY
   Elements and the Periodic Table
     Common elements and functions
     Atoms and isotopes
     Special function of electrons

 Compounds and chemical bonds
 Moles and molarity

 Chemical reactions
     General
     Oxidation/reduction reactions

 Water
 pH, buffers and salts
ELEMENTS
   A substance that cannot be
    broken down into simpler
    substances by normal
    chemical reactions.
   Each element is unique.
   Organized in the periodic
    table by atomic number.
   Each element is
    represented by an element
    key that shows its symbol,
    average atomic mass and
    atomic number.
THE PERIODIC TABLE
ABUNDANT ELEMENTS IN LIVING THINGS
   Carbon
       backbone of organic molecules


   Hydrogen & Oxygen
       components of water


   Nitrogen
       component of proteins and nucleic acids
ELEMENTS ARE COMPOSED OF ATOMS
   Atom Structure
       Nucleus contains 2 types of subatomic particles:
         Protons
         Neutrons

       Electron “cloud” surrounds the nucleus and contains
        1 type of subatomic particle:
           Electrons
ATOM FACTS
 Each proton and neutron has a mass of 1 AMU or
  Dalton. Each electron has a mass of 1/1800 AMU
  or Dalton.
 Atomic number =




   Atomic mass =
QUESTION
   If you have the atomic mass and atomic number
    for an element how do you find out how many
     Protons the element has?
     Electrons the element has?
     Neutrons the element has?
ATOMS AND ISOTOPES
   All elements have atoms with different atomic
    masses.
     The atom in the element key is the most abundant.
     The other atoms are called isotopes. The atomic
      masses and abundance of each are “averaged” for use
      in the element key.
     If all atoms of one element have the same atomic
      number or number of protons, what causes isotopes
      to have a different atomic mass?
ATOMS AND ISOTOPES
 Stable isotopes are happy but unstable isotopes
  are not and try to reduce their mass by releasing
  energy and radioactive particles.
 Each isotope “decays” at a certain rate. This is
  expressed as half-life.
 Half-life =
ELECTRON CLOUD
 Really orbits that electrons move in around the
  nucleus. Also called shells.
 Electron shells represent different energy levels.
  Electrons in shells close to the nucleus have less
  energy than those in outer shells.
ELECTRON CLOUD
   The electrons in the outermost shell are called
    valence electrons and determine the chemical
    properties of the atom. i.e. if they play with other
    atoms or not.
VALENCE ELECTRONS
 Atoms like to have 8 electrons in their outer shell
  – Octet Rule or Rule of Eights.
  Exception: atoms with only 1 shell are happy
  with 2 – He and H.
 If atoms have 8 valence electrons they don’t
  interact with other atoms.
 If they have less than eight they will either
  donate their extra electrons or try to steal
  electrons from another atom. This also means
  that they interact with one another.
VALENCE ELECTRONS
 When an atom loses or gains an electron it
  becomes an ion with an electrical charge. What
  kind of charge? HINT:
 Two atoms are walking down the street.

 Says one atom to the other, “Hey! I think I lost an
  electron!”
 The other atom says “are you sure?”

 The first atom says….
ATOMS AND IONS
   Atoms that gain an electron become

   Atoms that lose an electron become



   Significance: this is the basis for joining atoms
    together to form compounds and molecules and
    for harnessing the energy of the sun in
    photosynthesis.
ATOMS AND IONS
   When two atoms interact, they donate, steal or
    share valence electrons.

       When electrons are transferred from one atom to
        another, one atom becomes a cation and the other
        becomes an anion. Opposite charges cause an
        attraction and an ionic bond is formed.

       When electrons are shared by two or more atoms the
        bond formed is a covalent bond.
IONIC BONDS
COVALENT BONDS
   Some atoms share equally

   Some atoms share unequally

   Polar compounds like other polar compounds and
    non-polar compounds like other non-polar
    compounds.
        Example oil and water
HYDROGEN BONDS
   Relatively weak bonds that form between a H
    atom and usually an O or N atom.
MOLECULES AND COMPOUNDS
   Molecules –

   Compounds –

   Chemical formula – shows each atom and the
    numbers of each atom in the molecule or
    compound.

   Ex – CaCl2    NaHCO3      N3
MOLES
           Used to measure
            quantities of a substance.
           For any substance a mole
            = 6.02 X 1023 atoms,
            molecules or ions.
            **Avogadro’s Number.
           Molecular weight = mass
            of 1 mole of a substance in
            grams. Add the atomic
            masses of each atom in the
            substance.
           Ex. What is the molecular
            weight of NaCl?
MOLARITY
 Used to make solutions with certain quantities of
  a solute (substance) in 1.0 liter of a solvent, like
  water.
 A 1.0 M solution has 1 mole of the substance
  dissolved in 1 liter of a solvent.
CHEMICAL REACTION
 Involves making and/or breaking chemical bonds.
 General form: Reactants → Products.

 2 basic types:
CHEMICAL REACTIONS
   Important chemical reactions for harvesting
    energy from substances are called Redox or
    oxidation-reduction reactions. Electrons (energy)
    are transferred from a reducing agent to an
    oxidizing agent.
     Oxidation – an atom, ion or molecule loses electrons
      (energy).
     Reduction – an atom, ion or molecule gains electrons
      (energy).
     “Oil Rig”
WATER
 Water is a polar molecule formed by covalent
  bonds between the 2 H atoms and O.
 One end is slightly positive and the other end is
  slightly negative because of unequal sharing of
  electrons.
 Because it is polar, water is an excellent solvent
  for ionic or polar solutes.
                                           Oxygen part                   Hydrogen
                                                 Partial                 parts
                                               negative
                                              charge at                 Partial
                                           oxygen end                   positive
                                           of molecule                  charge
                                                                        at
Hydrogen (H)   Oxygen (O)   Hydrogen (H)                                hydrogen
                                                                        end of
                                                Water molecule (H2O)    molecule




                                                                       Fig. 2-7, p. 34
WATER
 Water molecules
  exhibit cohesion (stick
  to one another)
  because they form
  hydrogen bonds with
  one another.
 Water molecules
  exhibit adhesion (stick
  to other substances)
  by hydrogen bonding
  to substances with
  ionic or polar regions.
WATER IS A GOOD SOLVENT BECAUSE OF
ADHESION
WATER
 Hydrogen bonds between water
 molecules expand and make ice less
 dense than liquid water.

 Becauseice floats, the aquatic
 environment is less extreme.
Three Phases of Water
WATER
 Water  has high specific heat.
 Hydrogen bonds must break to raise
  water temperature.
 Specific heat of water helps:
WATER
 Waterhas a high heat of
 vaporization.
pH
 Means “parts hydrogen”.
 An application of molarity.

 Pure water (H2O) has some free ions H+ and OH-.
       The concentration of H+ (and OH- ) is 10-7M or
        0.0000001M.
       pH converts the concentration to a whole number.
       pH = -log of [H+]       so…
       pH H2O = -log of [10-7] The log of 10x = x so…
       pH H2O = - (-7) or 7
pH
   Pure water is
    considered neutral.
Buffers
 Important   for living organisms – pH
  homeostasis.
 Buffering system - based on a weak acid
  or a weak base.
 Buffers - resist changes in pH of a solution
  when acids or bases are added.
Salts
 Salt- a compound in which the
 hydrogen atom of an acid is replaced
 by some other cation.
     Ex. Na replaces H in HCl to form NaCl.
      provide many mineral ions
 Salts
 essential for life functions.

								
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