مواضيع علميه

المصدر: مواضيع علميه
في منتدى : قسم الكيمياء

Fundamental Units of Measure






Imagine that you find the following instructions in a laboratory procedure: “Transfer

1.5 of your sample to a 100 volumetric flask, and dilute to volume.” How do you
do this? Clearly these instructions are incomplete since the units of measurement
are not stated. Compare this with a complete instruction: “Transfer 1.5 g of your
sample to a 100-mL volumetric flask, and dilute to volume.” This is an instruction that you can easily follow.
Measurements usually consist of a unit and a number expressing the quantity
of that unit. Unfortunately, many different units may be used to express the same
​

 

Melamine



is an organic base and a trimer of cyanamide, with a 1,3,5-triazine skeleton. Like cyanamide, it contains 66% nitrogen by mass and, if mixed with resins, has fire retardant properties due to its release of nitrogen gas when burned or charred, and has several other industrial uses.
​

Melamine is combined with formaldehyde to produce melamine resin, a very durable thermosetting plastic used in Formica, and melamine foam, a polymeric cleaning product. The end products include countertops, dry erase boards, fabrics, glues, housewares and flame retardants. Melamine is one of the major components in Pigment Yellow 150, a colorant in inks and plastics.
Melamine also enters the fabrication of melamine poly-sulfonate used as superplasticizer for making high-resistance concrete
​

 

Chemical Reactions

​

science-4-all.bmp (image)

​

Chemical changes take place through
chemical reactions. Chemical symbols are
used to write chemical reactions in a chemical
equation. For example, when a mixture
of hydrogen gas (H2) and oxygen gas (O2)
ignites, the hydrogen and oxygen combine
to form water. A chemical equation expressing
the combination of hydrogen and oxygen
to form water is​

Let’s examine the chemical equation above
more closely. Hydrogen and oxygen are written
as molecules rather than atoms. Hydrogen,
oxygen, and a number of other gases
(Cl2, N2, Br2, I2) exist in their natural state as​

diatomic (two atoms) molecules. The reason
for this diatomic form becomes apparent
after we discuss electron configuration and
bonding. The plus sign in the equation
means “reacts with.” The equation states a
molecule of hydrogen reacts with a molecule
of oxygen to yield a water molecule
​

 

Atomic Structure


With the discovery of the neutron, a
basic atomic model consisting of three fundamental
subatomic particles was complete.
While discoveries were being made on the
composition of atoms, models were advanced
concerning the structure of the atom.
John Dalton considered atoms to be solid
spheres. In the mid-1800s, one theory considered
atoms to consist of vortices in an
ethereal continuous fluid. J.J. Thomson put
forth the idea that the negative electrons of
atoms were embedded in a positive sphere.
Thomson’s model was likened to raisins
representing electrons in a positive blob of
pudding; the model was termed the “plumpudding”
model as shown in Figure 4.3. The
negative and positive parts of the atom in
Thomson’s model canceled each other,
resulting in a neutral atom.
A clearer picture of the atom began to
emerge toward the end of the first decade
of the twentieth century
. ​

 

Spectroscopy and quantum mechanics


(devil)Spectroscopy is basically an experimental subject and is

concerned with the absorption,emission or scattering of electromagnetic radiation by atoms or molecules. As we shall see in, electromagnetic radiation covers a wide wavelength range, from radio waves to g-rays, and the atoms or molecules may be in the gas, liquid or solid phase or, of great importance in surface chemistry, adsorbed on a solid surface.
​

 

Hydrogen

Hydrogen


hydrogen is a , , , , highly with the H2. With an of 1.00794, hydrogen is the lightest element.
Hydrogen is the most chemical element, constituting roughly 75% of the universe's elemental mass. in the are mainly composed of hydrogen in its state.
​

 

Quantum numbers

The principal quantum number symbolized
by the letter n. The principal quantum
number tells which shell the electron is in
and can take on integral values starting
with 1. The higher the principal quantum
number, the farther the orbital is from the
nucleus. A higher principal quantum number
also indicates a higher energy level.
Letters may also be used to designate the
shell. Orbitals within the same shell have
the same principal quantum number
.​

 

Corrosion

Corrosion


All corrosion of steel in soil or water is electro-chemical in its origin and nature. There are certain conditions which must be met before a corrosion cell can function. They are:
1. There must be anodes (which are at higher potential) and cathodes (which are at higher potential).
2. There must be an electrical potential can result from a variety of conditions of pipelines
.​

 

Atomic Structure

Atomic Structure


Atomic Structure
With the discovery of the neutron, a
basic atomic model consisting of three fundamental
subatomic particles was complete.
While discoveries were being made on the
composition of atoms, models were advanced
concerning the structure of the atom.
John Dalton considered atoms to be solid
spheres. In the mid-1800s, one theory considered
atoms to consist of vortices in an
ethereal continuous fluid
​

 

اشكركم جميعا
المصدر