University POLITEHNICA Timisoara
Faculty of Industrial Chemistry and
Environmental Engineering
GENERAL CHEMISTRY
Assoc.Prof.dr.ing. Andrea Kellenberger
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GENERAL CHEMISTRY
Lecture: 2h / week
Laboratory: 2h / week
Evaluation form: Examination
Nr. of credits: 5
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INTRODUCTION
Chemistry is the science of substances.
Chemistry
studies
the
structure,
properties
and
transformation of substances.
Substances are charaterized by 2 essential properties:
homogeneity and constant composition.
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INTRODUCTION
Homogeneity = is the property of substances to show
same characteristics in all the volume.
Constant composition
= in any given portion of a
substance there are the same particles which interact in
the same way.
Substances can not be separated into other substances
by physical methods.
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INTRODUCTION
Exemple
of
substances:
water,
sugar,
oxygen,
hydrogen, sodium chloride, copper, hydrochloric acid,
sodiu hydroxide.
Air = substance?
Air is not a substance. By distillation of liquefied air
one obtains O2, N2 and other gases.
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INTRODUCTION
Gasoline = substance?
Gasoline is not a substance, because
by distillation it can be separated into
the component hydrocarbons.
NaCl solution = substance?
Sodium chloride solution is not a
substance, because by boiling the water is
removed and the NaCl crystals remains.
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INTRODUCTION
In nature, substances are found only rarely in pure form.
Materials are made ​of substances or mixtures of
substances.
Materials can be homogeneous sau heterogeneous.
Heterogeneous materials are composed of so-called
"phases" which are homogeneous portions separated
from other phases by areas where the properties vary
sharply.
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INTRODUCTION
Exemple of materials:
• metals
and
alloys.
Metals are homogeneous
materials
containing a
single metallic element.
Alloys are homogeneous
or
heterogeneous
mixtures of two or more
metals.
Alloys:
Brass = copper and zinc alloy
Bronze = copper-tin alloy
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INTRODUCTION
Exemple of materials:
• Wood
=
homogeneous
material,
composed of cellulose, lignin, resins
and other substances.
• Glass = usually a homogeneous
amorphous
material
(component
particles are not included in a crystal
lattice)
• Granite =
homogeneous
material
composed of three different minerals:
quartz, feldspar and mica.
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INTRODUCTION
Solutions = homogeneous mixture composed of two or
more substances. Solutions are obtained by dissolving
a substance called solute into another substance called
solvent.
Exemples
• liquid solutions
• solid solutions
• gaseous solutions
http://chemistry.about.com/od/imagesclipartstructures/ig/SciencePictures/Transition-Metal-Solutions.htm
10
INTRODUCTION
Liquid solutions:
• gas dissolved in liquid (CO2 in water)
• liquid dissolved in liquid (ethanol in water)
• solid dissolved in liquid (copper sulfate in
water, naphtalene in benzene)
Solid solutions = homogeneous alloys
Gaseous
solutions
=
homogeneous
mixtures of gases, i.e. air.
<a href="http://www.publicdomainpictures.net/view-image.php?image=15830&picture=bare-de-aur">Bare de aur</a> de
Petr Kratochvil
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INTRODUCTION
Each
substance
substances
by
is
distinguished
its
properties.
from
A
the
other
substance
is
characterized by its physical properties that can be
expressed by numerical values. For pure substances
these properties are called physical constants.
• melting point, boiling point
• density
• refractive index
• dielectric constant
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INTRODUCTION
International System of Units (S.I.).
S.I. has 7 fundamental units
Quantity
Unit
Symbol
meter
m
Mass
kilogram
kg
Time
second
s
Thermodynamic
temperature
Kelvin
K
Electric current
Ampere
A
Luminous intensity
candela
cd
mole
mol
Length
Amount of substance
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Derived units
Quantity
Equation
Name of the unit
Symbol
Area
S = l2
l – length
square meter
m2
Volume
V = l3
cubic meter
m3
Speed
v=l/t
t – time
meter per second
m s-1
Aceleration
a=v/t
meter per second squared
m s-2
Molar
concentration
cM = n / V
n- amount of substance
V-volume
mole per cubic meter
mol m-3
Force
F = m·a
m – mass
a – acceleration
kilogram· meter per second
squared (Newton)
kg· m s-2( N )
Pressure
P=F/S
S – area
kilogram· meter per square
second per square meter
kg· m s-2· m-2
N· m-2= Pa
Density
ρ=m/V
kilogram per cubic meter
kg· m-3
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I. ATOMIC STRUCTURE OF
SUBSTANCES
Since antiquity there is the idea that things in nature are
composed of very small particles, indivisible, called
atoms (atom, gr. = indivisible).
Atomic conception was resumed by J. Dalton in 1805,
who showed on the basis of experimental observations
accumulated until then that matter is made ​of atoms.
Avogadro's research related to gaseous state, led to the
discovery of molecules, where the atoms are bound
together in different ratios.
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I. STRUCTURE OF SUBSTANCES
Atom
=
basic
unit
of
matter,
indestructible by ordinary chemical
methods.
Molecule = the smallest particle of a
substance that can exist in the free
state and manifests the properties of
the substance.
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I. STRUCTURE OF SUBSTANCES
At the end of the 19th century, the English physicist J. J.
Thomson showed that the atoms of any element emit tiny
negative particles. He called the particles "corpuscles", but
later scientists preferred the name electron.
Although atoms contain negative particles, the whole
atom is not charged. So, Thomson concluded that atoms must
also contain positive particles to balance the negative charge of
the electrons. He imagined the “plum pudding model” of the
atom, in which electrons are scattered like plums into the
uniform “soup” or “cloud” of positive charges.
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I. STRUCTURE OF SUBSTANCES
Plum pudding model
electrons
cloud of positive charge
In this model, the atom is composed of electrons surrounded by
a “soup” of positive charge to balance the electrons' negative
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charges.
I. STRUCTURE OF SUBSTANCES
The “plum pudding” model was disapproved by
RUTHERFORD’s experience.
Rutherford measured the deviation of alpha particles
(helium ions with a positive charge) directed normally onto a
sheet of very thin gold foil. Since the mass of the electrons is
very small, and the α particles are heavy, considering the
plum pudding model, the alpha particles should pass through
the foil without significant deviation. The results of the
experiment were very different from what Rutherford
anticipated. Most of the α particles passed straight through
the foil, but some of them were deflected at large angles and
some were even reflected backward.
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Rutherford’s experiment
Expected results for the “plum
pudding model”
Observed results
“It was quite the most incredible event that has ever happened to me in my life. It was almost
as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit
you. … I realized that this scattering backward must be the result of a single collision, and
when I made calculations I saw that it was impossible to get anything of that order of
magnitude unless you took a system in which the greater part of the mass of the atom was
concentrated in a minute nucleus. It was then that I had the idea of an atom with a minute
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massive center, carrying a charge” — Ernest Rutherford
I. STRUCTURE OF SUBSTANCES
Conclusions:
• the plum pudding model for the atom could not be correct;
• the atom must contain a very small (compared with the size
of the atom) positive charge which causes the large
deflections of the α particles;
• the atom is mostly empty space because most of the α
particles passed directly through the foil.
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I. STRUCTURE OF SUBSTANCES
Based on these results, Rutherford proposed the
planetary model of the atom. According to this model the
atom is composed of 2 parts: a small, compact center of
positive charge called nucleus surrounded by a cloud of
tiny negative particles called electrons, moving around the
nucleus.
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I. STRUCTURE OF SUBSTANCES
Planetary model of the atom
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I. STRUCTURE OF SUBSTANCES
The planetary model of the atom is not perfect,
because it can not explain why electrons are not colliding
with the nucleus. It is known that an accelerating electric
charge emits electromagnetic waves, so electrons will
continuously lose energy, they will spiral towards the
nucleus and finally they will collide with the nucleus.
To explain why this did not occur, Niels Bohr (1913)
postulated:
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I. STRUCTURE OF SUBSTANCES
 Electrons can move around the nucleus only on certain
orbits, called allowed orbits.
 Electrons can gain or lose energy only by jumping from
one allowed orbit to another. When an electron moves
towards the nucleus energy is radiated and if it moves
away from the nucleus energy is absorbed.
 For an electron to remain in its orbit the electrostatic
attraction force between the electron and the nucleus
must equal to the centrifugal force which tends to throw
the electron out of its orbit.
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I. STRUCTURE OF SUBSTANCES
Niels Bohr
admitted that the
orbits of the
electrons are
circular.
Bohr’s model of the atom
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I. STRUCTURE OF SUBSTANCES
A. Sommerfeld (1916),
based on the atomic
spectra of hydrogen,
suggested
that
the
permissive orbits of the
electrons
may
be
elliptic.
Bohr – Sommerfeld model of the atom
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I. STRUCTURE OF SUBSTANCES
In 1919 Rutherford discovered that the nucleus
contains positive particles named protons. In 1932
James Chadwick discovered that nucleus contains also
neutral particles – neutrons. Protons and neutrons are
known as nucleons.
Nucleus
+ +
+ ++
++
+
+
+
Proton
Nucleons
Neutron
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I. STRUCTURE OF SUBSTANCES
Properties of the main subatomic particles
Electric charge
Mass
Symbol
[C]
Relative
charge
kg
amu
Proton
+1.602·10-19
+1
1.67262·10-27
1.0073
p; p+
Neutron
0
0
1.67493·10-27
1.0087
n; no
Electron
-1.602·10-19
-1
9.10939·10-31
0.0005486
e; e-
Proton = a nucleon with positive charge (+1)
Neutron = a nucleon with zero charge (0)
Protons and neutrons have close weights, and electrons are
much lighter.
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