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Chemistry: The Study of Change
Some Definitions First
CHEMISTRY studies MATTER.
MATTER is anything that has a mass and a volume.
Each of the particular kinds of matter (solid or liquid or gas) is
called a MATERIAL.
CHEMISTRY is thus defined as the science of the
composition and the structure of materials and of the
changes that the materials undergo.
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 1
Chemistry: The Study of Change
Chemistry is an Experimental Science and is
CENTRAL
All experimental sciences are based on observation, collecting data,
and analysing these in an SYSTEMATIC WAY.
This is known as THE SCIENTIFIC METHOD.
The scientific method is a systematic approach to
research.
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 2
Chemistry: The Study of Change
Scientific Method
When data are collected and represented, by equations, symbols, etc., next step is
form a hypothesis, a tentative explanation of observations. Observations may
be repeated to refine the hypothesis further.
When a large amount of data have been collected, they may be summarised in a
short-hand way by coming up with a mathematical equation. This is known as
a law.
Tested hypotheses result in a theory, a principle that explains facts and laws
that are based on them.
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 3
Chemistry: The Study of Change
Classification of Matter
Matter can be classified into two broad groups:
• Substances – this the type of matter that has definite composition
and distinct properties. Substances can be either elements or
compounds
• Mixtures – a combination of two or more substances, where the
substances retain their unique identities and can be separated by
physical means
• Mixtures can be homogeneous or heterogeneous
• Elements cannot be separated into simpler substances by chemical
means. There are 92 natural and 26 created elements. Each
element is identified by a symbol.
• Elements interact with one another to yield compounds, defined
as substances formed from two or more elements combined by
chemical means, with properties not similar to properties of the
constituent elements.
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 4
Chemistry: The Study of Change
Schematic Classification of Matter
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 5
Chemistry: The Study of Change
States of Matter
There are 3 states of matter:
• Solids – units packed in definite order
• Liquids – semi packed with some order
• Gases – no packing with units moving freely
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 6
Chemistry: The Study of Change
Physical and Chemical Properties of Matter
Substances are identified according to their properties and composition.
Physical properties of a substance can be measured and/or observed without
changing its composition or identity.
For example, melting of ice is a physical property of water, observed while it is
melting. Thus melting is a physical process.
Chemical properties of a substance can be observed during a chemical change.
For example, burning of hydrogen (an element) in air is a chemical property,
observed while it is burning. Thus burning is a chemical process.
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 7
Chemistry: The Study of Change
Extensive-Intensive Properties
All measurable properties of matter fall into either of the following additional
groups
Extensive Property – A property that depends on how much matter is under
study. For example, volume and mass of a sample of matter depends on the
amount of the sample. Extensive properties of the same kind can be added
together.
Intensive Property – A property that does not depend on how much matter is
under study. For example, temperature and pressure of a sample does not
depend on the amount of sample. Such properties are not additive.
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 8
Chemistry: The Study of Change
Measurements
Scientists use instruments (also called tools) to measure
macroscopic properties of substances directly. For example, a
ruler is used to measure the length of a sheet of paper.
Microscopic properties cannot be measured as such; indirect
methods have to be devised for these.
Each measurement results in a value. Depending on what tool
is used, this value may change. In order to have a unified
system across the scientific world, an international set of units
was agreed upon in 1960 and named as SI Units. This set has 7
base units for seven basic properties. All units for all other
properties can be derived from these.
These units are modified in decimal steps by a series of
prefixes.
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 9
Chemistry: The Study of Change
SI Units
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 10
Chemistry: The Study of Change
Some Other Common Units
Some quantities represented by SI Units are too large for
experimentation. It has been customary to use submultiples of these
in scientific research.
For example, we usually measure mass in grams (g) instead of
kilograms. Centimetres (cm) and millimetres (mm) may be more
convenient than metres.
Converting from one unit to another is a true mathematical
operation and is done via a conversion factor, which in fact, is a
proper mathematical equation.
For example, to change centimetres into metres we use this
conversion factor.
1 m  100 cm
General Chemistry I CHM 111
Dr Erdal Onurhan
Slide 11
Chemistry: The Study of Change
Precision and Accuracy
Accurate and
Precise
General Chemistry I CHM 111
Not Accurate
But Precise
Dr Erdal Onurhan
Neither Accurate
Nor Precise
Slide 12