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