Introduction to Science of Chemistry

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Introduction to Science of Chemistry

• Part - I
• Natural Science and Chemistry

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Natural Science

• Area of knowledge concerned with matter and
  energy
• Matter - anything that occupies space and has
  mass (or weight)
• Energy - that which is able to cause movement of
  matter

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Joesten Wood, World of Chemistry, 2nd,
Saunders,1996,4-5
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Definition of Chemistry

• Study of the composition, structure, and
  properties of matter, the changes which matter
  undergoes, and the energy released or absorbed
  during those changes
• Each of these concepts is examined in the
  following

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Composition of Matter - components of a sample of
matter
Modified from Siebring, B.R., Chemistry,MacMillan
, NY, 1967, 23
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Two Types of Definitions

• The preceding definitions concerning composition
  are called operational definitions - definitions
  based on sensory observations while manipulating
  matter
• Second type of definition is called theoretical -
  definition based directly or indirectly on atomic
  theory

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Theoretical Definitions for Composition
Element - sample consists of one kind of atom
Compound - sample consists of two or more kinds
of atoms combined in a fixed ratio that cannot be
varied
Mixture - sample consists of a collection of
elements and/or compounds present in ratios that
can be varied
http//users.rcn.com/jkimball.ma.ultranet/BiologyP
ages/M/Mixtures.html
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Models in Science

• Models represent objects in the imaginary
  submicroscopic world
• Picture models are drawings of mental images of
  atoms and related particles as we believe they
  would appear if our senses were superhuman

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Contd

• Physical Model - Material object that represents
  a mental image of atoms as we believe they would
  appear if our senses were superhuman
• Math models/computer models are equations,
  solvable by computers, that describe the behavior
  of matter

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Structure of Matter

• Types and relative locations of the component
  particles of a substance
• Types of particles are atoms, molecules
  (combinations of atoms), and ions (atoms bearing
  an electrical charge)
• Relative locations described using common
  geometrical terms

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Contd

• Particles in the imaginary world are represented
  by symbols - letter or combination of letters
• Atoms represented by letters H for hydrogen, O
  for oxygen, etc.
• Combinations of letters and numerical subscripts
  are called formulas and represent molecules such
  as H2O for water
• Letters with charges such as H and O2- represent
  ions

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Structures of Molecules
Angular
Linear
Angular
http//www.phyysicalgeography.net/fundamentals/6a.
html
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Ionic Substance Salt
Cubic Structure
http//www.phyysicalgeography.net/fundamentals/6a.
html
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Properties of Matter

• Characteristics which may be used to identify a
  substance (color, odor, etc.)
• Types of properties are physical (can be
  observed without change in composition - melting
  point) or chemical (requires a change in
  composition - electrolysis of water)

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Changes in Matter and Energy

• Types are physical (involves no change in
  composition - melting ice) or chemical (involves
  a change in composition - electrolysis of water)
• Changes in matter are accompanied by changes in
  energy endergonic change absorbs energy, and
  exergonic change releases energy

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Endergonic Physical Changes - no change in
composition
Melting
Boiling
Solid Ice
Ice, water, and steam are all have same
composition water molecules.
The solid, liquid and gas differ in the freedom
of motion of their component water molecules.
Peters,Chemistry.Brooks/Cole, 1997, M4
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Endergonic Chemical Change - electrolysis of
water changes composition to hydrogen and oxygen
Peters,Chemistry.Brooks/Cole, 1997, M4
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Joesten Wood, World of Chemistry, 2nd,
Saunders,1996,4-5
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Science of Chemistry

• Chemistry is based on observations in the real
  world where objects are large enough to be
  observed directly (macroscopic) or with aid of
  instruments (microscopic)
• Explanations of observations involve an imaginary
  world based on the Atomic Theory consisting of
  atoms, molecules and ions that are too small to
  be observed directly or with instruments
  (submicroscopic)

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Tro,N.J., Chemistry in Focus, Brooks/Cole,CA,1998,
9
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Real and Imaginary Views of Snow
Joesten, World of Chemistry, 2nd, Saunders, NY,
1996,27
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Methodology of Chemistry
Assumption all that is observed in the real
world is the result of interactions of atoms,
ions, and molecules with each other and/or with
energy
Observations in real world are used inductively
to construct and refine the model of matter
Model is used deductively to explain and predict
observations which serve as tests of the model
and later as bases of technologies
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Part II - Refinements to the Model of the Atom
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Size of Atoms

• Atoms are spheres having diameters that range
  between 0.5 x 10-8 and 2.6 x 10-8 cm
• Masses of atoms range from 10-24 to 10-28 g
• Atoms are so small that 300 M people ( US
  population) counting at rate of 1 atom/sec, would
  need 26 M years to count the atoms in a 10 g
  sample of Mg!

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Component Particles of Atoms
Particle Mass Charge Location in atom
Proton 1 amu 1 Nucleus
Neutron 1 amu 0 Nucleus
Electron 0 amu -1 Orbits
around nucleus
amu atomic mass unit 1.67 x 10-24 g
Nucleus center of a spherical atom
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Structure of Atoms

• Atoms consist of nucleus containing protons and
  neutrons surrounded by electrons moving in
  circular paths
• Diameter of nucleus 1/10000 of diameter of the
  atom

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Number of protons Z
Number of neutrons A - Z
Number of electrons Z - C
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Structure of Hydrogen Atom, H-1
The electron, which weighs only 1/1837 as much as
the proton, moves in a circle having a diameter
that is about 10,000 times as large as the
diameter of the nucleus making most of an atom
empty space.
If a person were the nucleus, the electron, on
the same relative scale, would be a sparrow
flying in circle with 2 mile radius!
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Explanation of Isotopes
Number of protons 6 6
Number of electrons 6 6
Number of neutrons 6 7
Short notation C-12 C-13
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Explanation of Atomic Weight

• Distribution of isotopes of all elements on the
  surface of Earth is essentially constant
• For carbon, 98.90 C-12 and 1.10 C-13
• Atomic weight is the mass of an average atom of
  an element
• Atomic weight of C (0.9890)(12) 0.0110(13)
  12.011 amu

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Explanation of Ions Ions result when atoms gain
or lose electrons
http//wine1.sb.fsu.edu/chm1045/notes/Atoms/Molecu
le/Atoms05.htm
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rine
Ions result from the transfer of electron(s) from
one atom to another
http//wine1.sb.fsu.edu/chm1045/notes/Atoms/Molecu
le/Atoms05.htm
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Part III - Periodic Table

• Systematic arrangement of the chemical elements

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Periodic Table

• Elements are arranged in order of increasing
  atomic numbers (Z)
• Elements with similar properties are placed in
  same columns (called families)
• H does not have unique location, but think of it
  as being between boron and carbon

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Tro,N.J., Chemistry in Focus, Brooks/Cole,CA,1998,
43
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Information Directly Provided by Periodic Table
Tro,N.J., Chemistry in Focus, Brooks/Cole,CA,1998,
43
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(No Transcript)
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Joesten,Essentials,Saunders, 1993, 3
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Explanations of States of Matter Using Models
Ice retains shape and volume independent of its
container
Steam assumes shape and volume of container
In ice, molecules attract each other so strongly
that they are unable to move relative to each
other
In steam, heat energy largely overcomes
attraction between molecules giving them relative
freedom of motion
http//www.visionlearning.com/module_viewer.php?mi
d49