Matter, measurement and the scientific method. Learn the basic words chemists use to describe what things are made of and how precisely we can measure them.
These terms were extracted from Chemistry by OpenStax, eCampusOntario (© 2016 Rice University; adapted by BCcampus) which is licensed under a Creative Commons Attribution 4.0 International License.
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study of the composition, properties, and interactions of matter
On your way to school, you stop to fill your car’s gas tank, almost making you late for the first day of chemistry class.
tentative explanation of observations that acts as a guide for gathering and checking information
Some routes involve a hypothesis, a tentative explanation of observations that acts as a guide for gathering and checking information.
statement that summarizes a vast number of experimental observations, and describes or predicts some aspect of the natural world
Doing chemistry involves attempting to answer questions and explain observations in terms of the laws and theories of chemistry, using procedures that are accepted by the scientific community.
realm of everyday things that are large enough to sense directly by human sight and touch
The macroscopic domain is familiar to us: It is the realm of everyday things that are large enough to be sensed directly by human sight or touch.
realm of things that are much too small to be sensed directly
The microscopic domain of chemistry is almost always visited in the imagination.
path of discovery that leads from question and observation to law or hypothesis to theory, combined with experimental verification of the hypothesis and any necessary modification of the theory
The path of discovery from question and observation to hypothesis, theory and experimental verification is called the scientific method.
specialized language used to represent components of the macroscopic and microscopic domains, such as chemical symbols, chemical formulas, chemical equations, graphs, drawings, and calculations
The symbolic domain contains the specialized language used to represent components of the macroscopic and microscopic domains.
well-substantiated, comprehensive, testable explanation of a particular aspect of nature
Mathematics, computer science, and information theory provide important tools that help us calculate, interpret, describe, and generally make sense of the chemical world.
smallest particle of an element that can enter into a chemical combination
However, most of the subjects in the microscopic domain of chemistry—such as atoms and molecules—are too small to be seen even with standard microscopes and often must be pictured in the mind.
pure substance that can be decomposed into two or more elements
Pure substances that can be broken down by chemical changes are called compounds.
substance that is composed of a single type of atom; a substance that cannot be decomposed by a chemical change
You may have heard of the Greek postulate that matter consists of four elements: earth, air, fire, and water.
state in which matter has neither definite volume nor shape
On your way to school, you stop to fill your car’s gas tank, almost making you late for the first day of chemistry class.
combination of substances with a composition that varies from point to point
A mixture with a composition that varies from point to point is called a heterogeneous mixture.
(also, solution) combination of substances with a composition that is uniform throughout
A homogeneous mixture, also called a solution, exhibits a uniform composition and appears visually the same throughout.
state of matter that has a definite volume but indefinite shape
That water is a liquid at moderate temperatures, will freeze to form a solid at lower temperatures, and boil to form a gas at higher temperatures (Figure 4) are macroscopic observations.
when matter converts from one type to another or changes form, there is no detectable change in the total amount of matter present
The law of conservation of matter summarizes many scientific observations about matter.
fundamental property indicating amount of matter
Matter is defined as anything that occupies space and has mass, and it is all around us.
anything that occupies space and has mass
Throughout human history, people have tried to convert matter into more useful forms.
matter that can be separated into its components by physical means
Matter can also have properties of more than one state when it is a mixture, such as with clouds.
bonded collection of two or more atoms of the same or different elements
However, most of the subjects in the microscopic domain of chemistry—such as atoms and molecules—are too small to be seen even with standard microscopes and often must be pictured in the mind.
gaseous state of matter containing a large number of electrically charged atoms and/or molecules
A fourth state of matter, plasma, occurs naturally in the interiors of stars.
homogeneous substance that has a constant composition
Two broad categories are mixtures and pure substances.
state of matter that is rigid, has a definite shape, and has a fairly constant volume
That water is a liquid at moderate temperatures, will freeze to form a solid at lower temperatures, and boil to form a gas at higher temperatures (Figure 4) are macroscopic observations.
force that gravity exerts on an object
Solids and liquids are more obviously matter: We can see that they take up space, and their weight tells us that they have mass.
change producing a different kind of matter from the original kind of matter
Pure substances that can be broken down by chemical changes are called compounds.
behavior that is related to the change of one kind of matter into another kind of matter
The change of one type of matter into another type (or the inability to change) is a chemical property.
property of a substance that depends on the amount of the substance
If the property depends on the amount of matter present, it is an extensive property.
property of a substance that is independent of the amount of the substance
If the property of a sample of matter does not depend on the amount of matter present, it is an intensive property.
change in the state or properties of matter that does not involve a change in its chemical composition
A mixture is composed of two or more types of matter that can be present in varying amounts and can be separated by physical changes, such as evaporation (you will learn more about this later).
characteristic of matter that is not associated with any change in its chemical composition
A physical property is a characteristic of matter that is not associated with a change in its chemical composition.
unit of temperature; water freezes at 0 °C and boils at 100 °C on this scale
The degree Celsius (°C) is also allowed in the SI system, with both the word “degree” and the degree symbol used for Celsius measurements.
volume of a cube with an edge length of exactly 1 cm
A cubic centimeter (cm³) is the volume of a cube with an edge length of exactly one centimeter.
SI unit of volume
The standard volume is a cubic meter (m³), a cube with an edge length of exactly one meter.
ratio of mass to volume for a substance or object
The macroscopic domain includes everyday and laboratory chemistry, where we observe and measure physical and chemical properties, or changes such as density, solubility, and flammability.
SI unit of temperature; 273.15 K = 0 ºC
The IUPAC convention is to use kelvin (all lowercase) for the word, K (uppercase) for the unit symbol, and neither the word “degree” nor the degree symbol (°).
standard SI unit of mass; 1 kg = approximately 2.2 pounds
For example, the maximum takeoff weight of a Boeing 777-200ER airliner is 298,000 kilograms, which can also be written as 2.98 × 10⁵ kg.
measure of one dimension of an object
For example, a length of 1000 meters is also called a kilometer because the prefix kilo means “one thousand,” which in scientific notation is 10³ (1 kilometer = 1000 m = 10³ m).
(also, cubic decimeter) unit of volume; 1 L = 1,000 cm³
A liter is the volume of a cube with an edge length of exactly one decimeter.
standard metric and SI unit of length; 1 m = approximately 1.094 yards
For example, a length of 1000 meters is also called a kilometer because the prefix kilo means “one thousand,” which in scientific notation is 10³ (1 kilometer = 1000 m = 10³ m).
1/1,000 of a liter; equal to 1 cm³
A cubic centimeter is also called a milliliter (mL) and is 1/1000 of a liter.
SI unit of time
It is now defined as the distance light in a vacuum travels in 1/299,792,458 of a second.
standards fixed by international agreement in the International System of Units (Le Système International d’Unités)
We usually report the results of scientific measurements in SI units, an updated version of the metric system, using the units listed in Table 2.
standard of comparison for measurements
Other elements, such as the gases hydrogen, nitrogen, oxygen, and chlorine, are composed of units that consist of pairs of atoms (Figure 6).
amount of space occupied by an object
Both liquid and solid samples have volumes that are very nearly independent of pressure.
how closely a measurement aligns with a correct value
Scientists typically make repeated measurements of a quantity to ensure the quality of their findings and to know both the precision and the accuracy of their results.
number derived by counting or by definition
The result of such a counting measurement is an example of an exact number.
how closely a measurement matches the same measurement when repeated
Scientists typically make repeated measurements of a quantity to ensure the quality of their findings and to know both the precision and the accuracy of their results.
procedure used to ensure that calculated results properly reflect the uncertainty in the measurements used in the calculation
(We will discuss the reason for rounding to the first decimal place in the next section.)
(also, significant digits) all of the measured digits in a determination, including the uncertain last digit
All of the digits in a measurement, including the uncertain last digit, are called significant figures or significant digits.
estimate of amount by which measurement differs from true value
While the number and unit are explicitly represented when a quantity is written, the uncertainty is an aspect of the measurement result that is more implicitly represented and will be discussed later.
(also, factor-label method) versatile mathematical approach that can be applied to computations ranging from simple unit conversions to more complex, multi-step calculations involving several different quantities
These calculations are examples of a versatile mathematical approach known as dimensional analysis (or the factor-label method).
unit of temperature; water freezes at 32 °F and boils at 212 °F on this scale
The conversion between these two units and the Fahrenheit scale will be discussed later in this chapter.
ratio of equivalent quantities expressed with different units; used to convert from one unit to a different unit
A ratio of two equivalent quantities expressed with different measurement units can be used as a unit conversion factor.