Introduction to Chemistry

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Introduction to Chemistry

• Ashton T. Griffin
• Wayne Community College
• Chapter 1 in both Silberberg McMurry Fay

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Goals Objectives

• The student will be able to identify the name and
  symbol of the first 36 elements on the periodic
  table. (I-1)
• The student will understand the common units of
  length, volume, mass, and temperature and their
  numerical prefixes. (1.5)

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Goals Objectives

• The student will understand the meaning of
  uncertainty in measurements and the use of
  significant figures and rounding. (1.6)
• The student will understand the distinction
  between accuracy and precision and between
  systematic and random error. (1.6)

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Master these Skills

• The student will be able to
• Use conversion factors in calculations (1.4 SP
  1.3-1.5)
• Find the density from mass and volume (SP 1.6)
• Convert between the Kelvin, Celsius, and
  Fahrenheit temperature scales (SP 1.7)

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Master these Skills

• The student will be able to
• Determine the number of significant figures (SP
  1.8) and rounding to the correct number of
  digits. (SP 1.9)

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Chemistry

• The science that deals with the structure,
  properties, and composition of matter and the
  changes that matter undergoes.
• Science--the study of
• Matter-- anything that has mass and occupies space

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Elements

• The simplest forms of matter
• Cannot be separated by chemical means into
  simpler stable substances
• Represented by symbols on the Periodic Table
• Learn the names and symbols for first 36 elements
  (I-1)

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Measurements in Chemistry

• always consists of two parts
• NUMBER
• EXACT or INEXACT
• SIGNIFICANT FIGURES
• SCIENTIFIC NOTATION
• UNIT
• METRIC SYSTEM
• DIMENSIONAL ANALYSIS

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Number

• Inexact Numbers
• Result of a physical measurement
• Numbers are limited by the instrument used to
  take the measurement.
• 14.3 gallons
• 14.325 gallons

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Number

• Exact Numbers
• Result of measurement of indivisible
  objects
• 10 tennis balls
• Some conversion factors
• Exactly 2.54 centimeters one inch

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Significant Figures

• Significant figures (sig figs or sig digs) are
  the digits in an inexact number.
• The last digit in an inexact number is an
  estimated value.
• The number of sig figs depends upon the
  instrument used.
• 14.3 gallons 14.325 gallons

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Significant Figures

• Exact numbers have an infinite number of
  significant figures.
• They do not contain an estimated value.
• 10.00000000 tennis balls
• 2.5400000 cm 1.0000000 inch

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Significant Figures

• When is zero a significant figure?
• Trailing zeros are always sig. figs.
• 11.0 ____ sig. figs.
• 100 ____ sig. figs.
• Trailing zeros are significant because they are
  the best estimate of the value.
• 10.9 11.0 (best estimate) 11.1

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Significant Figures

• When is zero a significant figure?
• Imbedded zeros are always sig. figs.
• 101 ____ sig. figs.
• 10.11 ____ sig. figs.
• Leading zeros are never sig. figs.
• 0.00145 ____ sig. figs.
• 0.0000000000234 ____ sig. figs.

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Scientific Notation

• Can be used to express very large or very small
  numbers
• Expresses value as A x 10n
• 1Alt10, n is an integer
• 14,345 1.4345 x 104
• 0.009867 9.867 x 10-3

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Scientific Notation

• Is useful for handling significant digits
• Express 14,345 to 3 sig. figs.
• 1.43 x 104
• Express 93,000,000 to 4 sig. Fig
• 9.300 x 107
• Express 0.009867 to 2 sig. figs.
• 9.9 x 10-3 or 0.0099

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Rounding Off Numbers

• Rule 1
• If the first digit to be dropped is less than 5,
  that digit and all the digits that follow it are
  simply dropped.
• Thus, 62.312 rounded off to 3 significant figures
  become 62.3.

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Rounding Off Numbers

• Rule 2
• If the first digit to be dropped is a digit
  greater than 5, or a 5 followed by digits other
  than all zeros, the excess digits are all dropped
  and the last retained digit is increased in value
  by one unit.

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Example of Rule 2

• Thus 62.782 and 62.558 rounded off to 3
  significant figures become, respectively, 62.8
  and 62.6.

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Rounding Off Numbers

• Rule 3
• If the first digit to be dropped is a 5 not
  followed by any other digit or a 5 followed only
  by zeros, an odd-even rule applies. Drop the 5
  and any zeros that follow it and then
• Increase the last retained digit by one unit if
  it is odd and leave the last retained digit the
  same if it is even.

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Example of Rule 3

• Thus, 62.650 and 62.350 rounded to 3 significant
  figures become, respectively, 62.6 (even rule)
  and 62.4 (odd rule). The number zero as a last
  retained digit is always considered an even
  number thus, 62.050 rounded to 3 significant
  figures becomes 62.0.

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Rounding

• Round each of the following numbers to 3
  significant figures
• 12.36
• 125.5
• 89.2532
• 58.22
• 12586.365
• 599.68

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Rules for Significant Figures in Answers

• For addition and subtraction. The answer has the
  same number of decimal places as there are in
  the measurement with the fewest decimal places.

Example adding two volumes
106.78 mL 106.8 mL
Example subtracting two volumes
863.0879 mL 863.1 mL
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Addition and Subtraction of Inexact Numbers

• Result will have a digit as far to the right as
  all the numbers have a digit in common
• 2.02 8.7397
• 1.234 -2.123
• 3.6923 6.6167
• 6.9463
• 6.95 6.617

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Multiplication and Division of Inexact Numbers

• The result can have no more sig. figs. than the
  least number of sig. figs. used to obtain the
  result.
• 4.242 x 1.23 5.21766 5.22
• 12.24/2.0 6.12 6.1

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Multiplication and Division of Inexact and Exact
Numbers

• Use of exact conversion factors retains the
  number of sig figs in the measured (inexact)
  value.
• 22.36 inches x 2.54 centimeters per inch 56.80
  centimeters
• Conversion factors involving powers of ten are
  always exact.
• 1 kilometer 1000 meters
• 3.5 kilometers 3.5 x 103 meters

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Rules for Significant Figures in Answers
Multiply the following numbers
23.4225 cm3 23 cm3
9.2 cm x 6.8 cm x 0.3744 cm
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Units

• Give the dimension being measured
• 14 (???)
• 14 feet (each containing five toes)
• 14 feet (each containing twelve inches)
• 14 light-years
• ALWAYS show units!
• in results and in calculations

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Units-- Metric System

• Mass kilogram(kg), gram(g)
• Length meter(m), centimeter(cm)
• Volume cubic meter(m3),
• cubic centimeter (cm3)
• liter(L) 1000 cm3 (exact)
• milliliter(mL) 1 cm3 (exact)
• Time second(s)
• Temperature Kelvin(K) Celsius (C)

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Additional SI Units

• Current Ampere
• Amount of Substance Mole
• Luminous Intensity Candela
• Four of these units are of particular interest to
  chemist.

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The Second

• Initially the second was tied to the Earths
  rotation. 1/86,400th of the mean solar day.
• In 1967, the second was based on the cesium-133
  atomic clock.

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The Meter

• In 1791, the meter was defined to be one
  ten-millionth of the length of the meridian
  passing through Paris from the equator to the
  North Pole.
• In 1889, a platinum-iridium bar was inscribed
  with two lines this became the standard for the
  meter.

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The Meter (continued)

• In 1960, the meter was based on the wavelength of
  krypton-86 radiation.
• Finally in 1983, the meter was re-defined as the
  length traveled by light in exactly 1/299,792,458
  of a second.

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The Kilogram

• In 1799, a platinum-iridium cylinder was
  fabricated to represent the mass of a cubic
  deciliter of water at 4 C. In new standard was
  created in 1879. Due to the changing nature its
  mass, it was suggested in 2005 that the kilogram
  be redefined in terms of fixed constants of
  nature.

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The Kilogram Standard
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The Mole

• Since the 1960s, the mole has been based on the
  number of atoms in 12.0 g of carbon-12 or 6.022 x
  1023 atoms.
• New attempts to define the mole include using a
  new standard Si-28.
• New attempts will continue.

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Units-- Metric System

• Use numerical prefixes for larger or smaller
  units
• Mega (M) 1000000 times unit (106)
• kilo (k) 1000 times unit (103)
• centi (c) 0.01 times unit (10-2)
• milli (m) 0.001 times unit (10-3)
• Micro (µ) 0.000001 times unit (10-6)

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Units -- Metric System

• Numerical Prefixes
• 12.5 m _______ cm
• 1.35 kg _______ g
• 0.0256 mm _______ µm
• 89.7 megahertz _______ hertz
• (1 hertz 1 cycle per second)

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Derived Quantities

• Frequency (cycles/s, hertz)
• Density (mass/volume, g/cm3)
• Speed (distance/time, m/s)
• Acceleration (distance/(time)2, m/s2)
• Force (mass x acceleration, kgm/s2, newton)
• Pressure (force/area, kg/(ms2), pascal)
• Energy (force x distance, kgm2/s2, joule)

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Dimensional Analysis

• Treats units like numbers
• Units cancel when multiplied or divided
• Set up equations so that unwanted units cancel
  and desired units remain
• How many miles will I travel in 3.00 hours at
  65.0 miles per hour?
• How long will it take to 500 miles at 65.0
  miles per hour?

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Dimensional Analysis

• Conversions
• Determine the number of oranges in 5.0 dozen
  oranges.
• Express 0.0045 grams in milligrams.
• Express 9.32 yards in meters.
• 2.54cm 1 inch (exact)

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Dimensional Analysis

• Derived quantities
• Determine the density of a substance(g/ml) if
  742g of it occupies 97.3 cubic centimeters.
• Determine the volume of a liquid having a
  density of 1.32 g/mL required to have 125 g of
  the liquid.

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