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 General chemistry

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Pulstars
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Masculin Nombre de messages : 2405
Age : 97
Loisirs : Sciences, épistémologie, esprit critique
Date d'inscription : 27/10/2004

MessageSujet: General chemistry   Dim 6 Aoû 2006 - 15:21

Let us take a material object of 1 meter long.
One cuts it into two, and one has two halves.
One takes one of the two halves, and one again cuts it into two.
And so on...

Would we indefinitely cut the length of an object, without never
finding a limit? No, and it is what I will explain to you.

This limit exists, and one will need even only 33 blows
scissors, over an initial length of 1 meter, to reach it.

This limit it is the atom, from the Greek word "atomos", meaning "indivisible" or "uncuttable".

The matter is thus discontinuous, but that, we do not have it
always known. Formerly, of the various beliefs told about the
nature of the matter, like the 4 elements (air, ground, water, fire)
or other myths which explain the universe.

An atom is the smallest unit of possible matter which characterizes
an object, its mass, its form, its aspect, its color, its glare, etc...

An atom is a corpuscle, a tiny particle, of which us
let us can represent itself under the appearance of a small sphere,
but it is only one appearance, because reality is very different, and
quantum physics describes these phenomena.

An atom is thus a particle, and its size is worth about
one dizième of billionth of meter, i.e. one can
to align approximately ten million atoms over a length of a millimetre.

All the existing matter is made up of atoms, in the form
solid, liquid or gas. The solids have tightened atoms the ones
on the others, they are in contact. The liquids have atoms a little
freer, and the movements are easier. The gases have atoms
who are agitated in all the directions.

The atoms are classified according to their mass and the quantity of particles that they contain themselves. Each atom is a kind of ball
who has a dense core made up of a bunch of protons
(positively charged particles) and of neutrons (particles neutral
electrically). The core is wrapped of a cloud of electrons
(negatively charged particles).

The phenomenon of electricity is described as follows : they are electrons
free which moves in a direction through an electric driver. The electrons thus transport the electric power.

The atomic nucleus with him only contains 99.99 % of the total mass of the atom. Each atom is characterized by the atomic number, which
is precisely the number of protons in the atom. Atomic mass
is the number of protons and neutrons.

In a given atom, a given number of protons (rigorously
equal to the number of electrons) characterizes the chemical element.
For example, an atom having only one proton is a hydrogen atom,
two protons it is helium, three protons it is lithium... until
92 protons which is the uranium atom.

There are 92 natural chemical elements, and a complement of atoms
artificial created by the man, like neptunium and plutonium.

When two chemical elements differ by their number of neutrons,
they are isotopes. For example, Uranium 235 and uranium 238, them
numbers attached are the atomic masses, the two isotopes differ
thus of 3 neutrons.

The atoms are not insulated, they can form chemical bonds,
to generate it are calls made up bodies.

For example, a body as water is composed, it contains the element
hydrogen and the element oxygenates. A molecule is a group of at least
two atoms which forms chemical bonds.

Chemistry is the study of the reactions between the atoms, and the methods
to manufacture the chemical compounds, or to separate the elements from
made up bodies.

Chemistry is a science and began its rise towards eighteenth
century, when the experimental and rational step was installation.

A simple principle characterizes the chemical reactions:
the total mass of the bodies which were used for the reaction is equal
with the total mass of the bodies which were produced.
In short, nothing is lost, nothing is not created, it thus does not have there creation
nor of destruction of the matter, but of a transformation of the matter.

I present here one of the chemical reactions to you simplest.
It is the formation of the water molecule starting from the simple elements
necessary to its manufacture.

2 H2 + O2 - > 2 H2O

Explanation of the reaction: we have two initial gases,
hydrogen and oxygen, we mix them, and let us ignite we them
with a source of energy (spark, flame), and the reaction occurs
in an explosive way (non luminous flame).

We will note in the chemical equation above that hydrogen
is symbolized by the letter H and oxygen by the letter O.
The figure placed after a chemical symbol indicates the number
of atom of the element given within the molecule. The figure
placed in front of the molecule or the atom the number of molecules indicates
or of atoms.

We will observe that 2 times will be needed more hydrogen molecules
that oxygen molecules to manufacture a water molecule.

Chemistry makes it possible to calculate the masses of the reactive bodies in order to start
reaction. The atomic mass of the hydrogen molecule is
of 2 grams per mole. The mole is a measuring unit, it is
the number of Avogadro (an always fixed number of atoms in a body).
A mole always contains 6.02 * 10^23 atoms or molecules.

The atomic mass of an oxygen molecule is 32 grams
by mole.

Then now, we will observe that 4 grams of hydrogen
mixed with 32 grams of oxygen will be able to produce 36 grams
of steam. With in premium a quantity of released heat.

While further going, the atoms are finally indivisible
and indivisible? Not, one can break them of pieces according to one
process named nuclear fission. The nuclear power relates to the cores
atomic. A particle like a neutron or a proton can
to make a core unstable and this one splits up in elements
lighter by releasing an important nuclear energy.
The element Uranium 235 (one of the isotopes) is fissile and can be used to produce energy in the form of heat, which is reconverted in electricity.
The opposite of fission is thermonuclear fusion, but it is more
difficult to implement: one needs an initial heat of some
million degrees Celsius to start the fusion of the atomic nuclei,
the light elements like hydrogen can be transformed into helium to produce a considerable energy. The sun is a kind
of natural engine of thermonuclear fusion, like all them
stars.

I hope that this small course of chemistry will have been useful to you, and thanks for your attention.
_________________
"At the bottom, one knows only when little is known; with the knowledge grows the doubt." (Goethe)
"I doubt thus I think" (Pulstars)

_________________
http://www.sceptiques.qc.ca/  

« On ne sait que lorsqu'on sait peu, avec le savoir croît le doute. » (Goethe)
« La qualité d’une expérience se mesure au nombre de théories qu’elle fait tomber. »
« Oser savoir en utilisant sa raison critique c’est le fondement de notre modernité, cela reste la condition de son avenir.» (Emmanuel Kant)
« Seul a un caractère scientifique ce qui peut être réfuté. Ce qui n'est pas réfutable relève de la magie ou de la mystique. » (Karl Popper)
« Une théorie est scientifique si et seulement si elle susceptible d'être réfutée ; elle n'est pas vraie, mais tout au plus admise provisoirement. » (Karl Popper)
« Toute connaissance accessible doit être atteinte par des méthodes scientifiques ; et ce que la science ne peut pas découvrir, l'humanité ne peut pas le connaître. » (Bertrand Russell)
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Dark Orionis
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Masculin Nombre de messages : 125
Age : 27
Localisation : Quelquepart dans le Bluck
Loisirs : Astrophysique
Date d'inscription : 22/05/2006

MessageSujet: Re: General chemistry   Lun 7 Aoû 2006 - 12:38

I found a software, a periodic table of the elements (or table of mendeliev), to download, click here.
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Pulstars
Univers
Univers
avatar

Masculin Nombre de messages : 2405
Age : 97
Loisirs : Sciences, épistémologie, esprit critique
Date d'inscription : 27/10/2004

MessageSujet: Re: General chemistry   Lun 7 Aoû 2006 - 12:53

Very interesting software, thanks a lot.

_________________
http://www.sceptiques.qc.ca/  

« On ne sait que lorsqu'on sait peu, avec le savoir croît le doute. » (Goethe)
« La qualité d’une expérience se mesure au nombre de théories qu’elle fait tomber. »
« Oser savoir en utilisant sa raison critique c’est le fondement de notre modernité, cela reste la condition de son avenir.» (Emmanuel Kant)
« Seul a un caractère scientifique ce qui peut être réfuté. Ce qui n'est pas réfutable relève de la magie ou de la mystique. » (Karl Popper)
« Une théorie est scientifique si et seulement si elle susceptible d'être réfutée ; elle n'est pas vraie, mais tout au plus admise provisoirement. » (Karl Popper)
« Toute connaissance accessible doit être atteinte par des méthodes scientifiques ; et ce que la science ne peut pas découvrir, l'humanité ne peut pas le connaître. » (Bertrand Russell)
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Dark Orionis
1 avertissement
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Masculin Nombre de messages : 125
Age : 27
Localisation : Quelquepart dans le Bluck
Loisirs : Astrophysique
Date d'inscription : 22/05/2006

MessageSujet: Re: General chemistry   Lun 7 Aoû 2006 - 13:28

Here a site extremely complete, it describes all the atoms, temperature of solidification, of vaporization, discoverer, a representation 3D is even available.

Look at here.
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