1.1 Chemistry: A science for the 21 century
Chemistry is the study of matter and the changes it undergoes.
Called the central science
1.3 The Scientific Method
Scientific method: a systematic approach to research.
1) Carefully define the problem
2) Performing experiments, making careful observations, and recording information/data about
3) Interpretation, meaning the scientist attempts to explain the observed phenomenon.
4) Based on the data, the researcher formulates a hypothesis ( a tentative explanation for a set
5) Further experiments are devised to test the validity of the hypothesis in as many ways as
6) After a large amount of data is collected, it is desirable to summarize the information in a
concise way, as a law. (law- a concise verbal or mathematical statement of a relationship
between a phenomena that is always the same under the same conditions)
Qualitative- consisting of general observations about the system
Quantitative- comprising numbers obtained by various measurements of the system
Isaac Newton’s second law of motion: force equals mass time acceleration (F = ma).
Theory- a unifying principle that explains a body of facts and/or those laws that are based on
Theories are constantly being tested. If a theory is disproved by an experiment, then it must be
discarded or modified so that it becomes consistent with experimental obsercations.
1.4 Classifications of Matter
Matter- anything that occupies space and has mass
Chemists distinguish among several subcategories of matter based on composition and
properties. The classifications of matter include substances, mixtures, elements, and
compounds, as well as atoms and molecules.
SUBSTANCES AND MIXTURES
Substance- a form of matter that has a definite (constant) composition and distinct properties.
Ex: water, ammonia, table sugar (sucrose), gold, and oxygen.
Substances differ from one another in composition and can be identified by their appearance,
smell, taste, and other properties.
Mixture- a combination of two or more substances in which the substances retain their distinct
Ex: air, soft drinks, milk, and cement.
Mixtures do not have constant composition.
Mixtures are either homogeneous or heterogeneous. Homogeneous mixture: the composition of the mixture is the same throughout. Ex: spoonful of
sugar dissolved in water.
Heterogeneous mixture: the composition is not uniform. Ex: sand mixed with iron filings, the
sand grains and the iron filings remain separate.
Any mixture, whether homogeneous or heterogeneous, can be created and then separated by
physical means into pure components without changing the identities of the components
ELEMENTS AND COMPOUNDS
Substances can either be elements or compounds.
Element: a substance that cannot be separated into simpler substances by chemical means.
Atoms of most elements can interact with one another to form compounds.
Compound: a substance composed of atoms of two or more elements chemically united in fixed
proportions. Ex: water.
Unlike mixtures, compounds can be separated only by chemical means into their pure
1.5 The three states of matter
All substances, at least in principle, can exist in three states: solid, liquid, gas.
Solid: molecules are held close together in an orderly fashion with little freedom of motion.
Liquid: molecules are held close together but are not held so rigidly in position and can move
past one another.
Gas: the molecules are separated by distances that are large compared with the size of the
The three states of matter can be interconverted without changing the composition of the
Melting point: solid to liquid
Boiling point: liquid to gas
1.6 Physical and chemical properties of matter
Substances are identified by their propertied as well as by their composition.
Color, melting point, and boiling point are all physical properties.
Physical property- can be measured and observed without changing the composition or identity
of a substance.
Ex: melting ice and helium gas being lighter than air.
Chemical property- to observe this property we must carry out a chemical change. Ex:
“hydrogen gas burns in oxygen gas to form water”.
After the change, the original chemical substance (the hydrogen gas), will have vanished, and all
that will be left is a different chemical substance (water).
Ex: hard-boiling an egg= chemical change All measurable properties of matter fall into one of two additional categories: extensive
properties and intensive properties.
The measured value of an Extensive property- depends on how much matter is being
Mass – the quantity of matter in a given sample of a substance (extensive property).
Values of the same extensive property can be added together.
Volume – length cubed. (extensive property).
The value of an extensive quantity depends on the amount of matter.
The measured value of an intensive property- does not depend on how much matter is being
Density- the mass of an object divided by its volume (intensive property).
Example of intensive property: temperature.
Unlike mass, length, and volume, temperature and other intensive properties are not additive
Meterstick- measures length or scale
Buret, pipet, graduated cylinder, volumetric flask- measures volume
Balance – measures mass
Macroscopic properties- can be determined directly.
Microscopic properties- on the atomic or molecular scale, must be determined by an indirect
SI UNITS (International System of Units)
Metric units: related decimally by powers of 10.
Base quantity Name of unit Symbol