Why to study chemistry?
Chemistry is the science
that studies the composition
and structure of matter and
the changes it undergoes.
Because everything in the
universe is composed of
matter, chemistry is the
study of our material world.
The chemical touches our lives
and influences our activities
in many ways that are often
called the nuclear science.
We chemistry practice all the
time in our daily activities,
i.e., the act of cooking,
washing, taking medicine,
fertilize the lawn, paint the
house, or light a match,
for example, are directly
related to this science.
In all these activities, substances
interact and chemical changes occur.
In our body when we breathe,
walk and suffer food
digestion, chemical
reactions occur regularly.
The environmental problems we
experience and we deal today, as
the disposal of domestic and
industrial wastewater, acid rain,
the greenhouse effect,
photochemical smog, among
many others, are all
primarily chemical problems.
Many goods are now made of polymers and
ceramics instead of wood and metal
thanks to our ability to produce materials
with properties not found in nature.
However, chemistry is essential in
the current revolution in molecular
biology, which is exploring the details
of how life is genetically controlled,
that is, no one today can
understand the modern
world without a basic
knowledge of chemistry.
Concepts Structure of Matter Basics
Matter and Atomic Theory
The word matter comes from the
real word, from the Latin.
In Latin, it means matter "what
that something is done".
The matter is all that make
up things that take up
space, which has weight and
that can impress our senses.
So, study the structure of matter is
to study how matter is organized.
The first manifestation
of genuine scientific
thought is traditionally
attributed to Thales,
who lived in the sixth
century BC the Greek city of
Miletus on the coast of Ionia
(now southeastern Turkey).
It is impossible to have the
exact measure of the effect
of new philosophical thinking
attributed to Thales.
Knowledge of Western
civilization is based on it.
Looking back, we can see that,
from its very beginning, this
new way of thinking contained
certain underlying assumptions.
These would determine (and more
than two and a half millennia later
still determining) both the form
and content of our knowledge.
Were assumptions that sustain all
subsequent scientific thought.
Tales asked the questions:
"Why do things happen as they do?"
And "What the world is
made and how it is done?"
By answering them, he assumed
that the answer should be
formulated regarding a basic
matter that the world It is made.
It also assumed that there is an
underlying unity to the world's diversity.
But perhaps the most
significant of all assumed
that there are answers
to these questions.
And those answers can be given
in the form of a theory - a word
derived from the Greek "look,
contemplate and speculate" - testable.
We know today that all
the matter in the universe
is made of atoms, but the
creation and characterization
of these atoms are still undefined
and has gone through many changes.
By its microscopic nature,
the atom can not be directly
visualized, and then imagined
a model for its description.
A model is made up of
knowledge, experience, and
tools available at the
time that is postulated.
The model is valid and
accepted as satisfactorily
explain the phenomena
observed to date.
When new facts are discovered
and are not explained
by the model, it is changed
or replaced by another.
The model is not a reality, but
one possibility envisioned
by the human mind, always
subject to evolution.
Just as the human body is composed
of cells, matter is composed
of atoms, and this is seen as
the fundamental unit of matter.
The concept that matter is
composed of tiny bits of
matter has come up with
Democritus (460-370 BC).
Democritus developed a theory that
the universe consists of space
and a number (almost) an infinite
number of invisible particles
which differ from each other in
form, position, and arrangement.
All matter is made of indivisible
particles called atoms.
The atomic concepts of Democritus
remained stable as rocks for
over two thousand years, only
complemented by John Dalton in 1804.
Between 1803 and 1804, John
Dalton established changes
in the atomic theory, which
were detailed in 1808.
Dalton introduced the concept
of discontinuity of matter.
It was the first scientific theory
held that the matter was composed of
atoms, bearing in mind that the theory
of Democritus, although correct,
was philosophical as it did not
rely on any rigorous experiment.
For his atomic theory,
Dalton made four postulates:
1 * - The field is divided
into indivisible and
unchangeable particles,
which are called atoms.
2 ** - All atoms of the same
element are identical to
each other, with the same
mass and the same properties.
3- The atoms of different elements
have different mass and properties.
4- The compounds are
formed when atoms combine
in a constant and
proportional relationship.
* We now know that atoms can be divided
and subject to change, and may
even be part of a converted mass
into energy by E = mc² relationship.
** The concept of isotopes introduced
later, changes the second assumption
since isotopes are atoms of the same
element that have different masses.
In Dalton season had been isolated
only 36 chemical elements and
still used come symbols of alchemy
to represent such elements.
Dalton himself was the author
of one of the symbologies.
The use of abstract symbols ended
only around 1813-1814 with
Berzelius, that in addition to
isolated calcium, barium, strontium,
silicon, titanium, and zirconium,
selenium also found, thorium and cesium.
When Berzelius decided, it was
time to change things he changed.
Given that the old symbols were
not easy to write, disfigured
the books and not collaborating
anything for your memory,
Berzelius proposed that the symbols
were represented by letters, based
on the first letter of the Latin
name of each elementary substance.
The electron discovery
In the nineteenth century, the works
of Heinrich Geissler (1859), Johann
Hittorf (1869) and William Crookes
(1886) experimentally showed that
when subjected to moderate pressures, the
gas can become electrical conductors.
To reach this conclusion, they used the
so-called cathode ray tube, i.e. a glass
bulb connected to a vacuum pump, which
aims to reduce the internal pressure.
In the two ends of the
metal tube there ends
(electrodes calls)
attached to a battery.
When the internal pressure reaches
about one-tenth of ambient pressure,
it is observed that the gas between
the electrodes starts to emit light.
When the pressure decreases
further (about one
hundred thousand times
lower than the ambient
pressure), the brightness
disappears, leaving
only a light spot behind
the positive pole.
Scientists attributed this
spot the rays (of unknown
origin) from the negative
pole, called the cathode.
These rays were called cathode rays.
The first breakthrough came with
the atomic model of Thomson, who
has used the electron to update
the model of Democritus / Dalton.
The atomic model of
Thomson, proposed in 1897,
had proposed an answer
to the question:
"How electrons and protons would
be distributed in the atom?".
Thomson suggested that the total
mass of the atom would be
due almost entirely only to the
positive charges (protons).
These would be spread
uniformly throughout
the sphere, forming a
compact, uniform mass.
In this mass surface would be
attached electrons, spaced uniformly.
This model became known as "plum pudding,"
which would resemble a covered pudding with
raisins in the pudding would be the mass
of positive charges and raisins electrons.
In this model already understood the
divisibility of the atom, but the atom
was regarded as a positively charged
sphere, with electrons spread around.
This model was accepted
until 1911 when Ernest
Rutherford proposed another
more improved model.
This new model originated from an exciting
experience, which will be described below.
The atom of Rutherford
The second and third major innovation came
with Ernest Rutherford in 1911 and 1912.
Rutherford was able to
create two atomic models are
still the most recognized of
the atom representations.
Rutherford first created a static model,
and subsequently a dynamic model.
To develop its atomic model
Rutherford experimented with alpha
particles from a sample of polonium
in an elaborate experiment.
Rutherford's experiment was to
launch a jet of α particles emitted
by polonium (a radioactive
element) on a thin golden plate,
to see whether these
particles would suffer any
deviation to pass by the
golden plate of atoms.
Rutherford made use of
this experiment in which
he tried to verify if
the atoms were massive,
using, for this, α particles, which have a
positive electrical charge, as projectiles.
The blade had to be fragile (0.001
mm thick), because it was known
that the alpha particles can not
penetrate thicker obstacles.
The blade need not necessarily
be gold, may be another metal.
However, gold has been
chosen to be very pliable
and therefore more suitable
for slide preparation.
The results showed three
different behaviors:
1. The most alpha particles
can pass through the
gold plate without
undergoing any deviation.
It indicates that these
particles do not find any
obstacles ahead and follow
your path straight.
2. Some α particles can
pass through the blade, but
suffering an unyielding
deviation in its path.
This fact shows that these
particles found some obstacle,
but not too large, as they
were crossing the blade atoms.
3. Very few alpha particles can
not penetrate the leaf and
return to the same side from
which they are released.
This fact shows that these
particles are an immovable
obstacle to collide at some
point of the blade atoms.
If the atom is equal to the model
previously proposed by Thomson as a compact
mass of positive charges distributed
uniformly throughout the metal,
then the alpha particles not suffer much
less substantial deviations would return.
Conclusions Rutherford
• The atom is not massive, with
an empty space than filled;
• The majority of the mass of
the atom is in a small central
region (the core) having positive
charge, where the protons;
• Electrons are located in a region around
the nucleus, called the electron cloud.
This model became known as "the solar system
model," where the sun would be represented
by the nucleus and the planets by the electrons
around the nucleus (in the electron).
Although sophisticated and accessible,
Rutherford's model had some problems because
he could not explain the spectral lines
of the chemical elements coherently
and also could not explain
the orbit of electrons.
According to the theory
of Rutherford, electrons
could orbit the nucleus
at any distance.
When electrons are circling
around the nucleus,
regularly would be
changing its direction.
The classical electrodynamics
(which deals with
the movement of electrons)
explains that such
electrons that always change
their direction, speed
or both, should continuously
emit radiation.
In doing so, they lose energy and
tend to spiral into the nucleus.
It means that atoms would be unstable,
completely contrary to the reality.
As the description of the
Rutherford atom is not entirely
correct, it did not clarify some
remarks that had been made.
Perhaps the most important
of these comments
were regarding the behavior
of certain gasses.
These gasses, low pressure,
emit light in a set of
discrete bands of the
electromagnetic spectrum.
It is entirely different from
the radiation emitted by solid
which is spread evenly across
the electromagnetic spectrum.
Emissions of these gasses radiation
were significant because
they showed that, at least
under some circumstances,
the orbits of the electrons can not
be at any distance from the nucleus,
but confined to discrete the same
distances (or particular energy states).
The Atom of Niels Bohr
The next significant evolution
in the understanding of
atomic structure came with the
atomic model of Niels Bohr.
However, due to the great sophistication of
this mathematical model and the succeeding,
the full sophisticated
understanding of the structure of
matter was limited to a select
group increasingly scientists.
It is curious that the increased
understanding of atomic
structure reduces the number
of people who understand.
The atomic theory of Bohr was
published between 1913 and 1915.
She was able to explain the
hydrogen atom spectrum
perfectly, the Rutherford
theory could not explain.
To this, Bohr accepted the dynamic model
of Rutherford with three postulates.
1- The electrons revolve around
the nucleus in circular orbits
(Rutherford model), but without
emitting radiant energy (steady state).
2- An atom emits energy in the form
of light only when an electron
jumps from an orbital of higher
energy to an orbital of lower energy.
ΔE = h.f, the energy emitted
is equal to the energy
difference of the two orbitals
involved in the jump.
3- Possible orbits are those
in which the electron
has an angular moment
integer multiple of h / 2π.
Thus, the third postulate tells us
that the electron can not be at any
distance from the nucleus, but it is
limited to a few possible orbits,
which are defined by a parameter
called the principal quantum number n.
(More details on quantum numbers
will be presented later)
n = 1,2,3,4,5,6, .... ∞
In the atomic model of Bohr, we note that:
1. The atomic model of Bohr explains
the primary spectrum of the
hydrogen atom and hydrogenic
atoms (with only one electron).
2. Let's calculate rays
and speed for hydrogen
and hydrogenic atoms (with
only one electron).
3. Does not explain the narrow spectrum.
4. Calculations rays and
speed to H and hydrogenic
atoms to high values of
n and Z lose meaning.
5. For a multi-electron atom, the radius
and speed of ideas lose their meaning.
6. Speed discontinuous, in
pulses, packets, or quanta.
7. Ray discontinuous in heels or wrists.
Application of the Bohr model
• Flame test;
• Fireworks;
• Bright and lamps (neon
and vapor lamps Na or Hg);
• Fluorescence and Phosphorescence;
• Laser ray;
• Bioluminescence: the light of fireflies;
The atomic model has continued to evolve.
Sommerfeld solved the problem appeared soon
after Niels Bohr enunciate its atomic model
because it was found that an electron in
a single layer, had different energies.
This fact could not be possible
if the orbits were circular.
Then Sommerfeld suggested that the
elliptical orbits were as ellipses
have different eccentricities, or
different distances from the center,
generating different energies
to a single electronic layer.
For this, Sommerfeld introduced
the azimuthal quantum
number, which defines the
orbit electron format.
For the primary quantum number equal to
1 (n = 1), the orbit may be spherical.
For n = 2 there are two
possible orbits shapes
(spherical l = 1, l =
0 and elliptical).
For any principal quantum number n,
there are n orbits of possible formats.
Using the theory of relativity,
Sommerfeld was able to explain
the unfolding of classical Balmer
series on the hydrogen atom.
Then, there were some more contributions
from other scientists, namely:
• Louis Victor de Broglie (1925):
suggests that the electron also features,
such as light, a dualistic nature of the
wave and particle (double standard),
explained later, in 1929,
the first diffraction an
electron beam obtained by
scientists Davisson and Germer.
• Werner Heisenberg (1927):
mathematically demonstrated that it
is impossible to determine at
the same time, position, speed,
and trajectory of a subatomic particle,
it is important to characterize
it for its power since it is not
possible to establish defined orbits.
This statement received
the Principle of
Uncertainty or Indeterminacy
name of Heisenberg.
• Erwin Schrödinger (1933): drawing
on the electron wave behavior,
established complex mathematical equations
that allow determining the energy and
regions of the probability of finding the
electron (orbital, not defined orbits).
Schrödinger received the Nobel
Prize for his work on quantum
mechanics Undulating and its
applications to atomic structure.
Definitely, it is abandoning the planetary
model of the Rutherford-Bohr atom
and appeared a new atomic model, the
quantum-mechanical model of the atom.
Atom Features
Atomic number (Z): is a number determined
experimentally characteristic of each element
representing the number
of protons contained
in the core and the
various features atoms.
In an electrically
neutral atom, the atomic
number is equal to the
number of electrons (e-).
In a neutral atom: Z = e
For example Sodium All
atoms have 11 protons;
therefore atomic number (Z) equal to 11.
All Iron atoms have 26 protons;
therefore, atomic number (Z) equal
to 26 mass number (A): The sum
of the number of protons and
neutrons in the nucleus of an atom.
A = number protons + neutrons No.
Number of Neutrons (n): In a neutral
atom, the number of positive charges
(protons) is equal to the number
of negative charges (electrons).
It can also be given by
the difference between
the mass number (A) and
the atomic number (Z).
n = e (if the atom is neutral) or n = A -
Z Atoms with electrical imbalance (ions)
• Cations are positively electrified
atoms, are atoms that have
more positive charges (protons)
than negative charges (electrons).
It occurs because the atom lost electrons.
The total number of
electrons lost equals the
total number of positive
charges acquired.
Examples: Na +, Ca ++, or Ca₂ +, Al₃ + ....
• Anions: atoms are negatively electrified.
These atoms have more
electrons than protons.
It occurs because the
atom electrons gained.
The total gains electrons are equal to
the total negative charges acquired.
Examples: Cl, the-- or O₂- ...
• Valence load indicates the number
of connections that an atom can hold.
As each connection is involved
one electron, the total
acquired loads, positive or
negative, determines the valence.
The cations and anions can be
Monovalent: Na +, Cl ........
Bivalent: Ca₂ +, O₂- ....
trivalent: Al₃ + P₃
........ tetravalent: PT₄
+ (SiO₄ ) 4- ........
• atomic mass (also called
atomic mass medium or medium
atomic weight) is the average
atomic mass of the isotopes.
Of the chemical element with
the carbon-12 as standard.
The atomic mass is
expressed in atomic mass
unit, u (formerly used
to represent as amu).
• Molecular weight: it
is the sum of the atomic
weights of all atoms
forming the molecule.
Example: Determination
of the molecular mass
of water H₂O: (1.0 x 2) +
(16 x 1) = 18u
• Mol: is the unit of measurement
of the amount of matter.
It is a basic unit of the
International System of Units (SI).
A mole of any substance has
6.023 x 1023 molecules.
For example, one mole of any gas molecules
has 6,023 x 1023 molecules of this gas.
One mole atoms of any element weigh
as many grams its molar mass, and
molar mass and atomic weight of the
element are numerically equal:
Example: Chlorine Atomic mass 35,5u =
Molar mass of chlorine = 35,5g / mol
• Molar mass: Molar mass is the mass
of moles of atoms of any element.
The molar mass of an element
is numerically equal
to the mass of the element
in atomic mass units.
Thus, the atomic mass of the
element informs its molar mass.
• Number of Avogadro: numerical constant
applied both in chemistry and in physics.
The formal definition of the Avogadro
number: the number of carbon-12
atoms in 0.012 kg (12g) Carbon-12,
which is approximately 6.02 x 10²³.
Avogadro's number can also be defined
as the number of elements in a mol.
Curiosity: Why always Carbon-12?
Historically, Carbon-12 is
chosen as a reference substance
because its atomic mass can
be measured very accurately.
• Molar Volume: The volume is measured in
liters occupied by a mole of substance.
The molar volume of gas
is constant for all
gasses to the same
pressure and temperature.
CNTP5 in the molar volume equals 22.71
L / mol, as the IUPAC6 guidelines.
Isotopes, isobars and isotones
• Isotopes: are atoms of the same element
that have identical chemical properties
(as they pose the same electronic distribution),
but different physical properties.
They have the same atomic number (Z)
but have different mass numbers (A).
• Isobars are atoms
having the same mass
number (A) but different
atomic numbers (Z).
Its chemical properties
are totally different.
• isotones are atoms with
different atomic and mass
numbers, but with the
same number of neutrons.
Measurement Units
In Chemistry, to perform any experiment,
in addition to the basic concepts
of matter and energy, it is also necessary
to know some measurement units.
The measurement of a
quantity is a number which
expresses a quantity compared
to a prescribed standard.
• Pasta (m) is the amount of
matter that exists in a body.
Determination of mass of a body
is made by comparison of its mass
initially unknown mass with other
previously known, a standard mass.
For this determination, it
uses a device called a scale.
• The Volume occupies a place
in space is a characteristic
of matter associated with
the quantity called volume.
In other words, the volume
of a portion expressed
matter how much space
is occupied by it.
The volume of a body is
determined by multiplying
its length by its
height and its width.
V = length x height x width
Great volume units are cubic
decimeter (dm³) per liter (L), cubic
centimeter (cc), milliliter
(mL) and the cubic meter (m³).
In the international
system (SI) the standard
unit of volume is the
cubic meter (m³).
However, the unit is further
used in the chemical liter (L).
General Properties of Matter
Are the properties of
matter observed in anybody,
regardless of the
substance that is made?
• Extension: property matter has
to occupy a place in space.
The volume is measuring
the extension of a body.
Your body, for example, has the
extension occupies the space you.
• Inertia: property matter
has to remain in the
situation you are in,
whether in motion, at rest.
The greater the mass of
a body, the harder it
is to change its movement
and greater inertia.
The mass is measuring
the inertia of a body.
• Impenetrability: Two bodies can not
occupy simultaneously the same space.
• Compressibility: the
property of matter that is to
have low volume when subjected
to a certain pressure.
• Elasticity: the property
that the matter has to return
its initial volume after
ceased the force acting on it.
• Severability: property
that the matter has
to be divided into smaller
and smaller parts.
Break a piece of chalk
to reduce it to dust.
How often have you shared the chalk?
• Indestructibility: matter can neither be
created nor destroyed, only transformed.
Ex. : When burned, the matter turns
into gasses, smoke, and ash.
Specific properties of matter
are the properties that
vary according to the substance
of the matter is made.
• Organoleptic: Color: matter
may be colored or colorless.
This property is perceived by sight;
Brightness: the ability
of a substance to reflect
light is what determines
its brightness.
We realize the brightness by sight;
Taste: Tasteless can be a
substance (taste) or flavored.
This property is perceived by taste;
Odor: matter can be odorless
(odorless) or citron (smelling).
This property is perceived by smell;
Form and physical state:
perceived by touch;
• Hardness: Resistance is
defined by the surface
offers when scratched
by another material.
The material is considered
harder than the other
when you can scratch that
another leaving a groove.
To determine the hardness of
materials used a scale of 1 to 10.
The value one corresponds to the less
hard mineral that is known, talc.
The value 10 is the hardness of
diamond, the hardest mineral known.
With it, one can cut and scratch
materials such as glass.
• Malleability: property that
allows the material to be molded.
There are pliable and non-pliable
materials. Ex.: cobre, silver, gold.
• Ductility: Property for
transforming materials into yarn.
Exs.: copper, silver, gold.
• Density: found through
reason (division) between
the mass of a substance and
the volume it occupies.
When we play several pieces
of cork in a container
with water, we find that
all float in the liquid.
Already we play to several
pieces of lead, all sink.
Some people try to explain this by
saying that lead is "heavier" than cork.
Interestingly, however,
a piece of mass 10 kg
cork floats, while a piece
of lead 1 kg sinks.
There is experimental that no
matter the dough: pieces of
cork floating in the water
and pieces of the lead sink.
After all, sink or float depends
on what feature of the object?
Density!
The density of an object or a
sample of some material or
substance is the result of
dividing its mass by its volume.
State of matter
All matter is made up of small particles
and, depending on the greater or
lesser degree of aggregation between them,
can be found, for teaching purposes,
in three physical states
(as, in fact, there are
five states of matter):
solid, liquid and gaseous.
The stones, ice, and wood are
examples of solid matter.
The water, milk, gasoline and
honey are in the liquid state.
But the hydrogen gas, oxygen gas, and
carbon dioxide are in a gaseous state.
Each of the three states
of aggregation has its
characteristics - such
as volume, density, and
form - which can be
changed by the change in
temperature (heating or
cooling) and pressure.
When a substance changes
state, undergoes changes
in its macroscopic
characteristics (size, shape,
etc.) and microscopic
(particle arrangement),
without, however, changes
in its composition.
Body
The body is a word that
comes from the Latin corpu.
A body is a limited portion of matter.
For example, the noun designates
Gold material, while a
gold bar designates a limited
portion of gold, a body.
System
From Latin and Greek
systema, meaning group.
Is any portion of the limited
physical space or not
containing matter and that
is the object of study.
It is synonymous with a
combination of parts coordinated
with each other and contribute
to a result or to form a set.
Environment
Excluding the system under study
is the rest of the universe.
Molecules
From Latin molecule, it
is the diminutive of
the soft Latin word,
which means large mass.
From the chemical point of
view, a molecule is the
smallest particle of an element
or a chemical compound
that can exist in the free
state and still possesses
all the properties of
that element or compound.
For example, the water molecule is formed
by two hydrogen atoms and an oxygen atom.
If this molecule is split no longer water,
but gaseous hydrogen and gaseous oxygen.
Types of transformations
By analyzing the changes
that matter can
undergo, there are two
types of transformation.
In one of the types, the transformation is
done and undone with relative ease and the
material retains its original composition
as folding and unfolding a sheet of paper.
The other type of transformation occurs
when the same sheet of paper on fire.
Note that the role is converted
into energy, smoke and ash, and
in this processing, the paper
will not return to the paper.
The transformations of materials, energy
or both receive the phenomenon name.
The phenomena can be divided into Chemical
Phenomena and Physical Phenomena.
• Chemical Phenomena: those
that cause changes in the
structure of matter, involving
chemical reactions.
For example, burn a note from a US
Dollar is a chemical phenomenon.
• Physical hazards are those
that do not cause changes in
the structure of matter, do not
involve chemical reactions.
For example, if you just
tear or fold a sheet of
paper, you are providing
a physical phenomenon.
Chemical elements
Everything that is
around you is made up of
one or more of the 114
elements known today.
A chemical substance is a key element ( a
group of atoms) that can be chemically
transformed or broken something simpler,
i.e. are pure substances existing in nature.
Silver, mercury and sulfur
are common examples.
Only 90 of the 114 known elements
present naturally occurring.
The remaining elements have
been artificially produced by
nuclear chemists using high-energy
particle accelerators.
Each chemical element is represented
by Chemical symbols with one or
two letters taken from their Latin
names, mostly, and other languages.
The names have different
origins, i.e., the popular
name of the material
that is found in nature,
some characteristic of the
substance, the name of
its discoverer, or even a
tribute to a scientist.
Examples: calcium comes
from calx Latin, lime;
Bromo, the bromos Greek, meaning stench;
Helium, discovered by
spectrum analysis of
sunlight, is the sun god
of the ancient Greeks;
and Nobelium, a tribute to the
Swedish physicist Alfred Nobel.
From the 111th element,
scientists differ on the
symbols to be used for
their representation.
The nomenclature most widely accepted
means of these elements by the
first letters corresponding to their
atomic number written out in Latin.
The atomic number element 114, for example,
is represented by Uuq (un-aquarium).
Compounds (or Chemical Substances)
A little over 100 chemical elements and
they form thousands of different chemicals!
How is this possible?
Only because the atoms of chemical
elements can gather forming
groups called clusters called
molecules or groups (or compounds)
ion (the difference between
one molecule and an ionic
compound is addressed in
chapter chemical bonds).
Each group forms a chemical.
The graphical representation of the chemical
composition of a substance using the
symbols and numerical indices eight is
called chemical formula of the substance
and indicates the constitution
of each unit forming substance.
For example, the chemical
formula of water is H₂O.
So when we say that the
chemical formula for
water is H₂O, we must
understand that each unit
of water is formed by the
combination of two atoms
of hydrogen and one
atom of element oxygen.
The most widely used
chemical formula The
molecular formula, (or
simply formula) indicating
the elements present in
the substance and how
many atoms of each element
are interconnected.
The other types are the gross
or minimal formula, proximate
formula, electronic formula
and the structural formula.
