Chapter 1 - Chemical Foundations
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
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
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
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
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
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?
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
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
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
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
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
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
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
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
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
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?
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
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
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
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