Chapter 1 Atoms and Elements

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					Chapter 1: Atoms and Elements

 KTT 111/3 – Inorganic Chemistry I

         Dr. Farook Adam

               August 2005
Chapter 1: Atoms and Elements
  Chemistry   is a science that studies the
   composition and properties of matter
  Matter is anything that takes up space
   and has mass
  Mass is a measure of the amount of
   matter in a sample
      Chemistry holds a unique place among the
       sciences because all things are composed
       of chemicals
      A knowledge of chemistry will be valuable
       whatever branch of science you study
 Chemistry is constantly changing as new
  discoveries are made by researchers
 Researchers use a commonsense approach to
  the study of natural phenomena called the
  scientific method
 A scientific study normally:
       Begins with a question about nature
       Involves a search of the work of others
       Requires observing the results of experiments
       Often results in a conclusion, or a statement based
        on what is thought about a series of observations

 Experiments    provide empirical facts
     Facts are called data
     A broad generalization based on the
      results of many experiments is called a
      (scientific) law
     Laws are often expressed as mathematical
     Laws summarize the results of

   Theoretical models attempt to explain why
    substances behave as they do

       A hypothesis is a tentative explanation
       A theory is an experimentally tested explanation
        of the behavior of nature

                          The scientific method is dynamic:
                          observations lead to laws, which
                          suggest new experiments, which
                          may lead to or change a hypothesis,
                          which may produce a theory.

 Chemical     substances are comprised of
 Atoms combine to form molecules
  which can be represented in a number
  of ways, including:

(a) Using chemical symbols and lines for “connections”
(b) A 3-D ball-and-stick model
(c) A 3-D space-filling model
 Characteristics or properties of
  materials distinguish one type of
  substance from another
 Properties can be classified as physical
  or chemical
     Physical properties can be observed
      without changing the chemical makeup of
      the substance
     Chemical properties involve a chemical
      change and result in different substances
     Chemical changes are described by
      chemical reactions
 Propertiescan also be described as
  intensive or extensive
      Intensive properties are independent of
       sample size
        • Examples: sample color and melting point
      Extensive properties depend on sample
        • Examples: sample volume and mass
   general, intensive properties are
 In
 more useful in identifying a substance
 Matter is often classified by properties

   The three common physical states of matter
    have different properties:

       Solids have a fixed shape and volume
         • Particles are close together and have restricted motion
       Liquids have indefinite shape but fixed volume
         • Particles are close together but are able to flow
       Gases have indefinite shape and volume
         • Particles are separated by lots of empty space

 Elements are substances that cannot
 be decomposed by chemical means into
 simpler substances

     element is assigned a unique
 Each
 chemical symbol
     Most are one or two letters
     First letter is always capitalized
     All remaining letters are lowercase
     Names and chemical symbols of the
      elements are listed on the inside front
      cover of the book
 Compounds     are substances formed from
  two or more different elements combined
  in a fixed proportion by mass
 The physical and chemical properties of
  a compound are, in general, different
  than the physical and chemical
  properties of the elements of which it is
 Elements and compounds are examples
  of pure substances whose composition
  is the same, regardless of source
A mixture consists of varying amounts
 of two or more elements or compounds
     Homogeneous mixtures or solutions
      have the same properties throughout the
     Heterogeneous mixtures consist of two
      or more phases
 Matter   can be classified:

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 We   take for granted the existence of
  atoms and molecules
 The concept of the atom had limited
  scientific usefulness until the discovery
  of two important laws: the Law of
  conservation of mass and the Law of
  Definite Proportions
 These laws summarized the results of
  the experimental observations of many

 Law    of Conservation of Mass:
      No detectable gain or loss of mass occurs
       in chemical reactions. Mass is conserved.
 Law    of Definite Proportions:
      In a given chemical compound, the
       elements are always combined in the same
       proportions by mass.
 Inthe sciences mass is measured in
  units of grams (symbol, g)
      One pound equals 453.6 g

   The laws of conservation of mass and
    definite proportions provided the
    experimental foundation for the atomic
   Dalton’s Atomic Theory (~1803 AD):
     •   Matter consists of tiny particles called atoms.
     •   Atoms are indestructible. In chemical reactions, the
         atoms rearrange but they do not themselves break
     •   In any sample of a pure element, all the atoms are
         identical in mass and other properties.
     •   The atoms of different elements differ in mass and
         other properties.
     •   In a given compound the constituent atoms are always
         present in the same fixed numerical ratio.

Support for Dalton’s Atomic Theory: The Law of Multiple Proportions
 Whenever two elements form more than one compound, the different
masses of one element that combine with the same mass of the other
element are in the ratio of small whole numbers.

                           Each molecule has one sulfur atom, and
                           therefore the same mass of sulfur. The
                           oxygen ratio is 3 to 2 by both mass and

                           Sample experimental data:
                                                  Mass Mass
                           Compound        Size    S      O
                           Sulfur dioxide 2.00 g 1.00 g 1.00 g
                           Sulfur trioxide 2.50 g 1.00 g 1.50 g

   It follows from Dalton’s Atomic Theory that
    atoms of an element have a constant,
    characteristic atomic mass or atomic weight

   For example, for any sample of hydrogen

         • F-to-H atom ratio: 1 to 1
         • F-to-H mass ratio: 19.0 to 1.00

       This is only possible if each fluorine atom is 19.0
        times heavier than each hydrogen atom

 Itturns out that most elements in nature
  are uniform mixtures of two or more
  kinds of atoms with slightly different
 Atoms of the same element with
  different masses are called isotopes
       • For example: there are 3 isotopes of hydrogen
         and 4 isotopes of iron
 Chemically,  isotopes have virtually
  identical chemical properties
 The relative proportions of the different
  isotopes are essentially constant
 A uniform mass scale for atoms requires a
 For atomic mass units (amu, given the
  symbol u) the standard is based on carbon:

       • 1 atom of carbon-12 = 12 u (exactly)
       • 1 u = 1/12 the mass of 1 atom of carbon-12 (exactly)

   This definition results in the assignment of
    approximately 1 u for the mass of hydrogen
    (the lightest atom)

          Example: Naturally occurring chlorine is a
           mixture of two isotopes. In every sample of this
           element, 75.77% of the atoms are chlorine-35
           and 24.23% are chlorine-37. The measured
           mass of chlorine-35 is 34.9689 u and that of
           chlorine-37 is 36.9659 u. Calculate the average
           atomic mass of chlorine.
                  Abundance Mass

Isotope             (%)       (u)               Contribution

Chlorine-35       75.77     34.9689         0.7577 * 34.9689 = 26.50 u
Chlorine-37       24.23     36.9659         0.2423 * 36.9659 = 8.957 u
                          (Rounded) Total                    = 35.46 u

    The average mass of 1 atom of chlorine in nature is 35.46 u.

            have been performed that
 Experiments
 show atoms are comprised of
 subatomic particles

 Thereare three principal kinds of
 subatomic particles:
    • Proton – carries a positive charge, found in the
    • Electron – carries a negative charge, found
      outside the nucleus, about 1/1800 the mass of a
    • Neutron – carries no charge, found in the
      nucleus, a bit heavier than a proton, about 1800
      times heavier than an electron                   22
 An  element can be defined as a
  substance whose atoms all contain the
  identical number of protons, called the
  atomic number (Z)
 Isotopes are distinguished by mass
  number (A):
       • Atomic number, Z = number of protons
       • Mass number, A = (number of protons) +
         (number of neutrons)
 Forcharge neutrality, the number of
 electrons and protons must be equal
 This     information can be summarized
      Example: For uranium-235
        • Number of protons = 92 ( = number of
        • Number of neutrons = 143
        • Atomic number (Z) = 92
        • Mass number (A) = 92 + 143 = 235
        • Chemical symbol = U
 Summary          for uranium-235:

        Mass number, A (protons + neutrons)  235
                         Chemical Symbol        U
      Atomic number, Z (number of protons)  92

The Periodic Table summarizes chemical and physical
  properties of the elements
 The first Periodic Tables were arranged by increasing
  atomic mass

                            Dmitri Mendeleev
                           Julius Lothar Meyer

    Both these researchers drew out the first periodic table
    independently of each other.

Mendeleev have been honored as
the first person to arrange the
elements in the form of a table
because he reported his findings to
the Russian Chemical Society a
few months earlier than Meyer!!!!

The Modern Periodic table is
arranged by increasing atomic

    Elements are arranged in
    numbered rows called periods

    The vertical columns are called
    groups or families (group
    labels vary)
   Modern   Periodic Table with group labels
      and chemical families identified


Note: Placement of elements 58 – 71 and 90 – 103 saves space

   Some important classifications:
       A groups = representative elements or main group

               I A = alkali metals
               II A = alkaline earth metals
               VII A = halogens
               VIII = noble gases

       B groups = transition elements
       Inner transition elements = elements 58 – 71 and
        90 – 103

               58 – 71 = lanthanide elements
               90 – 103 = actinide elements

 Classification   as metals, nonmetals, and

 Metals
     • Tend to shine (have metallic luster)
     • Can be hammered or rolled into thin sheets
       (malleable) and can be drawn into wire
     • Are solids at room temperature and conduct
 Nonmetals
     • Lack the properties of metals
     • React with metals to form (ionic) compounds
 Metalloids
     • Have properties between metals and
               The End

Do the exercises at the end of chapter ONE.
        For your own practice only!!
You do not have to pass up this assignment.

            Any questions?


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