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Atoms and Elements

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					        6.1: Atoms, Elements, and
               Compounds
 Chemistry is the study of matter.
 Matter is anything that has mass and takes up
  space.
 Atoms are the building blocks of matter.
 THE STRUCTURE OF ATOMS:
   Billions of atoms could fit on the head of a pin!
   Atoms are made up of even smaller particles –
       Neutrons
       Protons
       Electrons
The Structure of Atoms:
 Nucleus – the center of an atom
 Within this nucleus are protons and neutrons.
    Neutrons – particles that have no charge
    Protons – particles with a positive charge
 Electrons – negatively charged particles located
 outside the nucleus.
   Constantly move around the nucleus in energy levels.
   Are attracted to the protons
   Atoms contain an equal number of protons and
    neutrons so the overall charge of an atom is neutral.
An Atom:
Elements:
Elements:
 An element is a pure substance that cannot
  be broken down into other substances by
  chemical or physical means.
 Are made of only one type of atom.
 Information collected about each element
  has been organized into a chart called the
  periodic table of elements.
   Organized into horizontal rows called
    periods,
   And vertical columns called groups.
Carbon:
 Is an extremely important element in biology and
 chemistry because nearly all of the molecules of living
 things contain carbon.
Isotopes:
 Isotopes – atoms of the same element that have
  different numbers of neutrons.
 Mass number (A) = number of
protons and neutrons.
 Atomic number (Z)= number of
protons in the nucleus.
How many neutrons in Carbon 14?
 Neutrons have no charge so a change
In their number has no effect on charge.
 Carbon 14 is a radioactive isotope.
Radioactive Isotopes:
 A change in the number of neutrons CAN change the
    stability of the nucleus causing it to decay (or break
    apart).
   When a nucleus decays, it gives off radiation that can
    be detected and used for many applications.
   Isotopes that give off radiation are called radioactive
    isotopes.
   Carbon 14 is a radioactive isotope found in all
    living things.
   Half life – the amount of time it takes for half of the
    carbon 14 to decay.
Compounds
 Elements can combine to form more complex
  substances.
 Compounds are pure substances formed when two or
  more different elements combine.
   NaCl
   CaCl
   H2O
   CO2
6.2: Chemical Reactions
 Chemical reactions allow living things to grow,
  develop, reproduce, and adapt.
 The human body is a 24 hour reaction factory!
 A chemical reaction is the process by which atoms or
  groups of atoms in substances are reorganized into
  different substances. Chemical bonds are broken
  and/or formed during chemical reactions.
Rust forms when oxygen in the air
reacts with iron:
A light stick consists of a
glass vial, containing one
 chemical solution, housed
inside a larger plastic vial,
containing another solution.
When you bend the plastic vial,
the glass vial breaks, the two
solutions flow together, and the
resulting chemical reaction
causes a fluorescent dye to emit
light.
Physical Changes
 It’s important to know that substances can undergo
  changes that do not involve chemical reactions.
 Water, for example, can undergo physical changes:
Reactants and Products
 A chemical equation shows the reactants on the right
    side of an arrow, and the products on the left.
   Reactants – the starting substances of a chemical
    reaction.
   Products – The substances formed during the
    reaction.
   Reactants          Products
   C6H12O6 + O2         6CO2 + 6H2O
   Glucose and oxygen react to form carbon dioxide and
    water. (This is cellular respiration.)
   In chemical reactions, matter cannot be created not
    destroyed. All chemical equations must show a
    balance of mass.
Section 6.3: Water and Solutions
 Properties of water (H2O):
    Water is a polar molecule – it has an unequal
     distribution of charges.
    Hydrogen bonds – a weak attraction involving a
     hydrogen atom and an oxygen atom. This is a van der
     Waals force which is responsible for keeping water
     molecules together.
    Water has surface tension due to van der Waals forces.
        Water striders can stand on water.
        Water droplets can form.
Mixtures
 A mixture is a combination of two or more substances
 in which each substance retains its individual
 characteristics and properties.
   Homogenous mixture – uniform composition
    throughout
   Heterogenous mixture – components remain distinct,
    do not dissolve
 A solution is a homogenous mixture. Two
 components of a solution are:
   Solvent – substance in which another substance is
    dissolved
   Solute – the substance that is dissolved in the solvent.
Acids and Bases:
 Acids are substances that release hydrogen ions
  when dissolved in water.
 The more hydrogen ions a substance releases, the
  more acidic the solution becomes.
 Substances that release hydroxide ions (OH-)
  when dissolved in water are called bases.
   NaOH is a common base that breaks apart in water to
    release Na+ and OH- ions. The more OH- ions present,
    the more basic a solution is.
pH:
The amount of hydrogen ions
or hydroxide ions in a
solution determines the
strength of an acid or a base.
We can easily measure the pH
of a solution using a pH
meter or pH paper.
See the pH scale to the right.
Water is neutral (pH 7)
Acids have a pH lower than
that of water.
Bases have a pH higher than
that of water.
What’s a buffer?
  WARM-UP:
  1. List the atoms involved in photosynthesis.
  2. List the molecules involved in photosynthesis.
  3. List the compounds involved in photosynthesis.



Photosynthesis Equation:
                      Solar
 6CO2     6H2O       energy        C6H12O6        6O2
Cellular Respiration:
Carbohydrates + oxygen = carbon dioxide + water +
energy


Chemical Equation for Cellular
Respiration:
 C6H12O       6O2                   6H2        energ
    6                     6CO2
                                     O           y

				
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posted:10/12/2011
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