مواضيع علميه

الموضوع في 'قسم الكيمياء' بواسطة star_2121, بتاريخ ‏مارس 7, 2009.

  1. star_2121

    star_2121 Active Member

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    المصدر: مواضيع علميه
    في منتدى : قسم الكيمياء


    Fundamental Units of Measure



    [​IMG]


    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
  2. star_2121

    star_2121 Active Member

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    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
    EBN EL NEAL و chemistry معجبون بهذا.
  3. star_2121

    star_2121 Active Member

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    Chemical Reactions


    science-4-all.bmp (image)
    [​IMG]


    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
    chemistry و EBN EL NEAL معجبون بهذا.
  4. star_2121

    star_2121 Active Member

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    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
    .
    toto11 و chemistry معجبون بهذا.
  5. AHMED FIRST

    AHMED FIRST مستشار كلية العلوم ملك الحصريات إداري

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    الجنس:
    ذكر
    الوظيفة:
    Researcher
    مكان الإقامة:
    مـصــــــــــــــــر


    thankssssssssssssssssssss
    (hi)​
  6. chemistry

    chemistry مستشار كلية العلوم النهرالخالد إداري

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    أم الدنيا مصـر


    جزاك الله الجنة أخى الكريم
  7. star_2121

    star_2121 Active Member

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    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.
  8. star_2121

    star_2121 Active Member

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    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.
  9. star_2121

    star_2121 Active Member

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    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
    .
  10. star_2121

    star_2121 Active Member

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    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
    .
  11. star_2121

    star_2121 Active Member

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    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
  12. star_2121

    star_2121 Active Member

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