Chapter 1- Chemical Foundations

1.1 Chemistry: An Overview

• We cannot see the atoms with the naked eye; we must use a special microscope called a scanning tunneling microscope (STM)

  • The STM uses an electron current from a tiny needle to probe the surface of a substance

  • The atoms are connected to one another by bridges

• The nature of these atoms is quite complex and the components of atoms do not behave much like the objects we see in this macroscopic world

• Atoms are organized in a given substance that determines the properties of that substance

  • Water is composed of two types of atoms: hydrogen and oxygen

  • When an electric current passes through, water is decomposed to hydrogen and oxygen, which makes them be two-atom molecules

1.2 The Scientific Method

• Make observations. Observations may be qualitative or quantitative. A qualitative does not involve a number. A quantitative observation is also known as measurement involves a number and a unit

• Formulating hypotheses. A hypothesis is a possible explanation for an observation

• Performing experiments. This involves gathering new information that enables scientists to decide whether the hypothesis is valid

• Observation: something that is witnessed and can be recorded

• Theory: an interpretation

  • Theories are human inventions that represent attempts to explain observed  natural behavior

  • It is actually an educated guess

• Natural law: observed behavior into a statement

• The coupling of observations and hypotheses occurs because once we begin to proceed down a given rhetorical path, our hypotheses are unavoidably couched in the language of that theory

• This focusing process may limit our ability to see other possible explanations

  • Science is affected by profit motives, budgets, fads, wars, and religious belief

  • The progress of science is more affected by the frailties of humans and their institutions than by the limitations of the scientific devices

1.3 Units of Measurement

• A measurement always consists of two parts: a number and a scale

• Units can be very important and can mean the difference between life and death on some occasions

• Volume

  • It is derived from length

  • An example: The average height of an adult male is 1.8 m.

• Mass

  • It is measured by the force necessary to give an object a certain acceleration

  • Body mass is the same on the earth and the moon

  • Weighing something on a chemical balance involves comparing the mass of that object to a standard mass

• Weight

  • It is the force that gravity uses on an object to measure its mass

  • It varies with the strength of the gravitational field

1.4 Uncertainty in Measurement

• Certain digits: Results that show the first three numbers that remain the same regardless of who makes the measurements

• Uncertain digits: The digit to the right of the 1 must be estimated and varies

• They report a measurement by recording all the certain digits plus the first uncertain digit

• It is important to indicate the uncertainty in any measurement

  • Significant figures indicate the uncertainty in a measurement

• Precision

  • It refers to the degree of agreement among several measurements of the same quantity

  • It is often used as an indication of accuracy

• Accuracy

  • It refers to an agreement of a particular value with a true value

  • This can be applied to a single measurement but is more commonly applied to the mean value of repeated measurements

1.5 Significant Figures and Calculations

• Non zero integers: They always count as significant figures

• Leading zeros: Zeros that precede all the nonzero digits

• Captive zeros: Zeros between the nonzero digits

• Trailing zeros: Zeros at the right end of the number

• Exact numbers: Arise from the definitions, they can be assumed to have an infinite number of significant figures

• Example to count scientific figures

  • The number 0.000070 is more much conveniently represented as 7.0 x 10^-5

1.6 Learning to Solve Problems Systematically

• The best way to approach a problem is to ask questions such as:

  • What is my goal? Where am I going?

  • Where am I starting?

  • How do I proceed from where I start to where I want to go?

1.7 Dimensional Analysis

• It is the best way to convert a given result from one system of units to another

• Examples: You want to order a bicycle with a 25.5 in frame. The size is 25.5 inches

  • Convert from inches to centimeters

  • We need the equivalence statement, which is 2.54 cm = 1 in.

  • 25.5 in × 25.4 cm/ 1 in = 64.8 cm

• The speed limit on many highways in the United States is 55 mi/h. What number would be posted in kilometers per hour?

  • 55 mi/ h × 1760 yd/ 1 mi × 1 m/1.094 yd. × 1 km/ 1000 m = 88 km/h

  • All units cancel except the desired kilometers per hour

• While doing chemistry problems, you should always include the units for the quantities used

1.8 Temperature

• The Celsius scale

• The Kelvin scale

• Fahrenheit scale (used in engineering sciences)

• Both the Celsius and Kelvin scale are used in physical sciences

  • The fundamental difference between the two temperature scales is there zero points

  • Conversion between the two: Temperature (Kelvin)  = temperature (Celsius) + 273.15

  • Temperature (Celsius) = temperature (Kelvin) - 273.15

• Converting between Fahrenheit and Celsius scales is more complicated because both the degree sizes and the zero points are different

• You can simply memorize the equations, or you can take the time to learn the difference between the temperature scales and to understand the processes involved in converting scales

1.9 Density

• It is the mass of a substance per unit volume of the substance

• What is the density measurement used for?

  • The liquid in your car’s lead storage battery changes density because the sulfuric acid is consumed as the battery discharges

  • Density measurement is also used to determine the amount of antifreeze and the level of protection against freezing

1.10 Classification of Matter

• The matter is complex and has many levels of the organization

• The three states of matter are solid, liquid, and gas

• Solid is rigid and has a fixed volume

• A liquid has a definite volume but no specific shape

• A gas has no fixed volume or shape

• Wood, gasoline, wine, soil, and air are the mixtures

  • They can be classified as homogeneous or heterogeneous

• Mixtures can be separated into pure substances by physical methods

  • Water is a good illustration of this idea

• Physical change: It is used to separate a used mixture into pure compounds and change in the form of a substance

• Distillation is one of the most important methods for separating the components of a mixture

  • The one-stage distillation works very well when only one component of the mixture is volatile

  • When a mixture contains several volatile components, the one-step distillation does not give a pure substance in the receiving flasks, and more elaborate methods are required

• Filtration: A mixture poured onto a mesh, which passes the liquid and leaves the solid behind

• Chromatology: The general name applied to a series of methods that use a system with two phases of matter (mobile phase and stationary phase)

• When a mixture is separated, the absolute purity of the separated components is an ideal

• Pure substances are either compounds or free elements