Ch. 1: Chemical Foundations·Chemistry: An Overview What is matter made of ?
Scanning Tunneling Microscope (STM) The Nobel Prize in Physics 1986 L: Heinrich Rohrerb(b1933), R: Gerd Binnig(1947), IBM Zurich Research Laboratory Rüschlikon, Switzerland
Figure 1.01c: Scanning tunneling microscope image showing rows of ring-shaped clusters of benzene molecules on a rhodium surface.
Figure 1.3: Sand on a beach looks uniform from a distance, but up close the irregular sand grains are visible.
Oxygen atom, hydrogen atom, water molecule ＊Substances are made of ~100 atoms
Steps in the Scientific Method • 1. Observations • quantitative • qualitative • 2. Formulating hypotheses • possible explanation for the observation • 3. Performing experiments • gathering new information to decide • whether the hypothesis is valid
Outcomes Over the Long-Term • Theory (Model) • A set of tested hypotheses that give an • overall explanation of some natural phenomenon. • Natural Law • The same observation applies to many • different systems • Example - Law of Conservation of Mass
Law vs. Theory • A law summarizes what happens; • A theory (model) is an attempt to explain why it happens.
However, we tend to see what we expect to see and often fail to notice things that we do not expect. Thus the theory we are testing helps us because it focuses our questions. However, this focusing process may limit our ability to see other possible explanation. It is also important to keep in mind that scientists are human. They have prejudices; they misinterpret data; they become emotionally attached to their theory and thus lose objectivity; and they play politics. Science is affected by profit motives, budgets, fads, wars, and religious beliefs. The scientific methods are only as effective as the humans using them. They do not automatically lead to progress.
Nature of Measurement • Measurement - quantitative observation consisting of 2 parts • Part 1 - number • Part 2 - scale (unit) • Examples: • 20 grams • 6.63 Joule seconds
International System • Based on metric system and units derived from metric system. English System
Figure 1.6: Measurement of volume 1 liter = 1000 cm3 = 1000 mL
Figure 1.7: Common types of laboratory equipment used to measure liquid volume.
Uncertainty in Measurement • A digit that must be estimated is called uncertain. A measurement always has some degree of uncertainty.
Figure 1.9: Measurement of volume using a buret. The volume is read at the bottom of the liquid curve (called the meniscus).
Precision and Accuracy • Accuracy refers to the agreement of a particular value with the truevalue. • Precisionrefers to the degree of agreement among several elements of the same quantity.
Figure 1.10: The results of several dart throws show the difference between precise and accurate.
Types of Error • Random Error (Indeterminate Error) - measurement has an equal probability of being high or low. • Systematic Error (Determinate Error) - Occurs in the same directioneach time (high or low), often resulting from poor technique.
Type of Errors: (1). Determinate (or systematic) error: Can be detected, measured, and eliminated; affect the accuracy of results. 1. Instrument errors -Calibration 2. Method errors -Analysis of standard samples -Independent analysis -Blank determinations -Variation in sample size 3. Personal errors -Care and self-discipline (2). Indeterminate (or random) errors: Cannot predict exactly a results from examination of other results; affect the precision of measurement. -Overall uncertainty.
Precision and Accuracy (exercise 1.2) Volume shown by Volume shown Trial graduated cylinder by the buret -------------------------------------------------------------------------- 1 25 mL 26.54 mL 2 25 mL 26.51 mL 3 25 mL 26.60 mL 4 25 mL 26.49 mL 5 25 mL 26.57 mL Average 25 mL 26.54 mL Results: Good precision for a graduated cylinder. This graduated cylinder is not very accurate. It has systematic error.
Rules for Counting Significant Figures - Overview • 1. Nonzero integers • 2. Zeros • leading zeros • captive zeros • trailing zeros • Exact numbers • Exact numbers were determined by counting, not obtained from measurement.
Rules for Counting Significant Figures - Details • Nonzero integersalways count as significant figures. • 3456 has • 4 sig figs.
Rules for Counting Significant Figures - Details • Zeros • Leading zeros do not count as • significant figures. • 0.0486 has • 3 sig figs.
Rules for Counting Significant Figures - Details • Zeros • Captive zeros always count as • significant figures. • 16.07 has • 4 sig figs.
Rules for Counting Significant Figures - Details • Zeros • Trailing zeros are significant only • if the number contains a decimal point. • 9.300 has • 4 sig figs.
Rules for Counting Significant Figures - Details • Exact numbershave an infinite number of significant figures. • 1 inch = 2.54 cm, exactly
Rules for Significant Figures in Mathematical Operations • Multiplication and Division: # sig figs in the result equals the number in the least precise measurement used in the calculation. • 6.38 2.0 = • 12.76 13 (2 sig figs)
Rules for Significant Figures in Mathematical Operations • Addition and Subtraction: # sig figs in the result equals the number of decimal places in the least precise measurement. • 6.8 + 11.934 = • 18.734 18.7 (3 sig figs)
Dimensional Analysis Proper use of “unit factors” leads to proper units in your answer.
Temperature • Celsius scale =C • Kelvin scale = K • Fahrenheit scale =F
Density • Density is the mass of substance per unit • volume of the substance:
Classification of Matter • Three States of Matter: • Solid: rigid - fixed volume and shape • Liquid: definite volume but assumes the shape of its container • Gas: no fixed volume or shape - assumes the shape of its container
Figure 1.13: The three states of water (where red spheres represent oxygen atoms and blue spheres represent hydrogen atoms).
Types of Mixtures • Mixtures have variable composition. • Ahomogeneous mixtureis a solution (for example, vinegar) • Aheterogeneous mixtureis, to the naked eye, clearly not uniform (for example, a bottle of ranch dressing)