Chapter 1 Chemistry as a Science – The Study of Matter and its Changes
Chemistry is the science that deals with the structure and properties of matter and its changes. It is part of
the spectrum of natural sciences, specifically the physical sciences, its context shown in the following
table:
Table 1.1
The material world in the environment consists of various chemical substances and materials either in the
pure form (the pure chemical) or as association with other substances known as mixtures. Mixtures are
either homogeneous or heterogeneous, depending on the degree of subdivision of the particles. If the
“naked” eye can still identify different areas of particulate matter, the mixture is “obviously
heterogeneous. Otherwise, if the mixture gives a uniform appearance as if it were a pure substance, the
mixture is considered homogeneous. Of course there will be some point where even an apparent
homogeneous mixture will reveal an uneven distribution of its constituent components, for example under
a microscope, so the transition is gradual.
Fig. 1.1
Fresh milk is a homogeneous mixture since the dispersion of water and fat droplets is so fine, that no
particulates can be discerned and the particle distribution seems uniform throughout. It “pretends” to be a
pure, single substance even though it is complex mixture of many chemicals. It consists of many pure
substances such as various fat, protein and sugar molecules, as well as vitamins and minerals and today
possibly growth hormones and antibiotics. Once it spoils or becomes sour, however, it changes into a
lumpy, watery mix and becomes heterogeneous. Fresh buttermilk, on the other hand, is heterogeneous to
begin with, if it has the desired buttery flakes floating within it.
Any pure substance can be represented by a specific formula, a short-hand symbol to signify that
particular chemical such as H2O for water. This formula indicates the elements involved in the compound
and their bonding ratio in one building unit that at the same time represents the whole chemical. One
wouldn’t drink another liquid consisting of the same elements but connected by a different ratio, namely
Hydrogen Peroxide with the formula H2O2. This chemical is more suited for bleaching and disinfecting, a
property that water does not have.
Fig. 1.2
Fig 1.3
Fig. 1.4
Some formulas are simple, some much more complex such as Ca10(PO4)6(OH)2 for the mineral apatite
found in bones and teeth or C184H282N50O60S for Exenatide, a peptide hormone found in the saliva of the
Gila Monster, a poisonous reptile living in the southwestern part of the United States, and used as a drug
to treat diabetes mellitus type 2.
Pure substances are not widely distributed in nature, usually being associated loosely or intrinsically with
other chemicals, so mixtures are the predominant form of matter and the chemist has the burden of
finding appropriate separation techniques. Mixtures come in various sorts. The following table shows
various types of mixtures based on the physical states involved:
Table 1.2
Air is a homogeneous mixture of various gases such as hydrogen, oxygen, nitrogen, carbon dioxide,
helium, water vapor and others. When contaminated with particulate matter such as dust, soot, nitric
oxide, or water droplets it can be classified as smog, smoke, fog etc., with a spectrum of homogeneous or
heterogeneous gradations. Even microbes are known to inhabit the air. So the atmosphere is already a bag
of different chemicals, living and non-living.
Fig. 1.5
Special types of mixtures are colloids. They can be comprised of different phases as mentioned above.
The particulate matter dispersed in the dispersion medium (continuous phase) has dimensions, however,
that come close to the wavelength of visible light ( 𝜆: 400 − 750 𝑛𝑚). This case allows scattering of
light, which is passed through an otherwise clear colloidal solution, to occur, known as the Tyndall
Effect (John Tyndall, 1820-1893, British).
Fig.1.6
Once matter is separated into non-degradable pure substances, the latter can be identified, classified, and
utilized. The behavior can be studied and properties classified as either physical or chemical in nature.
Physical properties relate to physical conditions such as appearance, temperatures that produce a change
in physical state given by the conversion points - melting/ freezing point, Mp/Fp; boiling/condensation
point, Bp/Cp , the relative ability to absorb or exchange heat, density and specific gravity, electrolytic
behavior, ability to conduct electricity, magnetic properties , solubility, polarity, polymorphism etc. Any
property that does not involve a change in the chemical identity of a substance, retaining its specific
formula, is considered physical. Any change in chemical identity by reacting with other substances to
form chemicals with new identities and formulas is considered chemical. General reactivity, flammability,
combustion ability, giving certain reactions with reagents like color change, gas evolution, or
precipitation, stability, photosensitivity etc. are all chemical properties. Chemical behavior can always be
expressed in a chemical equation, which denotes a chemical change – reactants yielding products.
Reactants → products
“Equation” means that no atoms are produced or destroyed during a chemical change, that the Law of
Conservation of Mass is observed. Instead of the equal sign (=), the “yield” arrow (→) is used,
indicating that “old” chemicals lead into “new” ones. However, equations can also be used for physical
changes, especially when one form of a chemical is converted into another, like physical state changes or
conversion into other allotropic forms.
I2 (S) → I2 (g) (sublimation of Iodine)
Cgraphite → Cdiamond
During a chemical change the products formed represent completely new entities with their own
characteristic physical and chemical properties, that often have nothing in common with the reactants and
do not represent an average of the reacting substances.
The following image contrasts the chemical change and the physical change involved with the burning of
a copper wire:
Fig.1.7
As mentioned before, the formula is the “blueprint” or identification tag of a given chemical. The line-up
of all the elements involved in a given compound with the subscripts involving the relative bonding ratios
of the atoms involved is considered the molecular formula such as MgCl2 or C2H6O. However,
occasionally two or more chemicals happen to have the same molecular formula but different alignment
of the atoms or structure. These are called isomers and are more common in Organic Chemistry, or the
chemistry of hydrocarbon compounds and their derivatives. For instance the molecular formula C2H6O
can represent an ether or an alcohol:
CH3OCH3 (Dimethylether); CH3CH2OH (Ethanol)
Chemistry is based on the atom as building block for all elements and compounds and the interaction of
the electrons (atomic sub-particles) for the establishment of chemical bonds, holding the atoms of the
different elements in some kind of arrangement together. The various atomic theories and the nature of
the chemical bond will be described in more detail in later chapters. For this introductory chapter a
working knowledge of the atom, as rudimentary concept for the understanding of the “rules of the game”
is laid out. The ancient Greeks - mainly Democritus – had already introduced the concept of the atom,
being “atomos”, the ultimate, indivisible grain or particle of which all matter is composed.
Fig. 1.8
According to recorded records of scientific history, Dalton was the first to re-adopt the concept of the
atom as universal, indivisible building block of the material world. He set up four postulates for his
atomic theory.
According to Dalton’s Atomic Theory:
1. All materials are made up of atoms
2. All elements in nature consist of one specific type of atom
3. Each compound is made of atoms of different elements in distinct whole number ratios
4. Atoms are neither destroyed or produced during a chemical change only involving a re-shuffling
of the atoms from old combinations into new combinations
He devised his own symbols for the atoms of different elements, as is shown in the following table:
Table 1.2
These have nothing in common with present-day representations, which consist of one or two letter
symbols of the Latin alphabet, in which the first letter is always capitalized and the second written in
lower case, such as N (Nitrogen) and Au (Gold from “Aurum”). Many elements were already known back
in time. However, since many were bonded with other elements, such as many metals in the form of ores
(metallic oxides and sulfides) and others “trapped” in salts and minerals, chemical work-up procedures
were necessary to warrant their discovery and identification. Today all the possible, stable or less stable
naturally occurring elements are known and grouped in the 2-dimensional Periodic Table of the
elements, which comprises all the elementary substances found throughout the universe as well as the
artificially produced elements in recent years. Nuclear bombardment experiments can lead to new
elements, however unstable and short-lived.
Each element, as Dalton already postulated, consists of one type of atom, different in size and reactivity.
The properties can only be attributed to a collective of the same atoms, which make up the specific
element. The atom alone has no physical properties. Mercury (Hg from “Hygrargyrum” meaning
quicksilver or liquid silver ) as an element only consisting of mercury atoms. This element can react with
Oxygen of the air to the compound Mercuric Oxide or Mercury (II) oxide. Oxygen is a gas made up of
diatomic groups of individual oxygen atoms, always occurring as two atoms paired together as molecular
entities. It is therefore considered a diatomic element or a molecular instead of an atomic element. Others
of this sort are Hydrogen (H2), Nitrogen (N2), and the Halogens (F2, Cl2 etc.).
Many elements with the historical context of their name are listed below:
Table 1.3
The raw, unbalanced equation for the worded reaction “Mercury reacts with Oxygen to give Mercuric
Oxide” is:
Hg + O2 → HgO
Since “equation “ means that the number of atoms for each side of the chemical change must be equal,
meaning according to Dalton’s postulate and the conservation law of mass that the atoms only disengage
themselves from old combinations of the reactant side to enter into new associations on the product side,
the equation must be balanced. This is done by changing the coefficients or the numbers in front of the
formula, never the subscripts, which are part of the chemical identity. If the HgO is changed to HgO 2, a
completely new compound is implied, which was not the intended outcome of the reaction. By keeping
true to the chemical identities of the reaction, the balanced equation would thus become:
2Hg + O2 → 2HgO
By multiplying the coefficient times the subscript, an inventory of the atoms left and right can be easily
carried out:
Atoms (reactant side)
Atoms (product side)
2Hg
2Hg
2O
2O
The formula HgO signifies the compound in general but also one entity or unit of this compound. Since it
is not a molecular compound, the term used in this case is the formula unit, a building block or unit that
is repeated many times in the context of a crystal structure. Molecules are chemically bound atoms in a
specific ratio that have an independent existence, even in a solid crystalline phase, where they are held
together by weaker, intermolecular forces. H2O would be an example of a molecular compound.
Example Problem 1.1
How many total atoms are involved in each of the following formula units?
CaCl2
C2H5OH
Fe3(PO4)2
Example Problem 1.2 Which of the following materials are a pure substance or a mixture of
different substances?
Sand
Epsom salt
Coffee
Modern copper penny
Example Problem 1.3
Complete and balance the following reactions:
H2 + O2 →
C + O2 →
Fe +
S
→
The combinatory variety of the elements to different compounds is endless and has no bounds. Chemistry
is one of the most productive sciences. A major part of chemical research is to synthesize consistently
new products with novel properties and applications.
Effective chemical investigations and understanding are grounded on well-postulated theories and
principles. Dalton’s Atomic theory gave a jump-start to chemistry as an exact, natural science and led the
way to the Scientific Method for further study into the chemical and physical relationships of nature.
The word “Chemistry” comes from the Arabic word “al khimia”. At first the word was adopted in the
form of “Alchemy”, a significant precursor, based originally on the goal of transmuting base metals into
more precious, nobler forms and finding the “stone of wisdom” as well as the secret for eternal life among
others, for modern day Chemistry. The Arabs and later the Europeans in medieval times, made already
significant chemical observations and introduced functional glassware and techniques that are essential
for laboratory studies and still in use in modern laboratories of today. Although founded on a different
philosophy, all these endeavors ultimately established and advanced chemistry as a strict academic and
exact empirical science. Chemical observations and manipulations were carried out by many peoples
around the world. The Chinese were pioneers in the development of explosives, gunpowder and
chemicals for fireworks, Africans developed sophisticated smelting furnaces, the Amazon Indians
produced methods for isolating natural products such as Curare for their poison arrows. The list goes on
and on.
Fig. 1.9
Fig. 1.10
The first use of the modern scientific method relying on observations, reliable and repeatable
measurements is mainly attributed to the French Chemist, Lavoisier, the discoverer of Oxygen and often
referred to as the “Father of Chemistry”. He worked with his wife and others in well-equipped
laboratories but was later one of the nobility victims of the French Revolution.
From then on Chemistry made tremendous strides as a body of knowledge, making it necessary, to
subdivide the whole field into separate disciplines, as shown in the scheme below:
Some overlaps occur and new fields of study emerge as time goes on, such as computational chemistry,
medicinal chemistry, bio-inorganic chemistry to name a few.
Part of the growth is due to the refinement of older and development of newer methods of instrumentation
and the help of computerization in data collection and evaluation as well as imaging.
A research concept always starts the same. Observers of nature or existing research by others see certain
connections, discrepancies or problems. They come up with a hypothesis, an educated guess or tentative
solution, then devising a set of experiments or protocol to test the hypothesis, modify or re-evaluate their
battery of experiments, if conflicting results occur until a set of significant and repeatable data can be
collected and evaluated into a meaningful conclusion. The latter can then be expressed as a postulate or
theory and published in the scientific literature, after a satisfactorily peer review has been obtained.
Fig. 1.7
Today changes are underway from the traditional methods, including un-biased internet representation or
payment based open publications. The earlier scientific journals allowed their contributors to battle out
their competing opinions and grievances.
If a theory is so well established and of universal truth it becomes a law, such as the Law of Gravity, the
gas laws and conservation of mass and energy laws. However, a theory can be replaced by a “better”
theory, outdated, dismissed as wrong, or just ousted by political force or fashionable ideas held by the
majority of the scientific community.
Theories that were outmoded and dismissed were the “Phlogiston Theory”, the “Universal Ether Theory”,
the “Land-Bridge Theory” among others.
All exact sciences are based on the empirical (based on experience) collection of data obtained and
collected by accurate and precise measurements. The next chapter will elaborate on the methods of
scientific measurements and the rules required for their mathematical evaluation.