شرح كيمياء الصف الثاني الثانوي لغات - الفصل الدراسي الأول
شرح كيمستري تانية ثانوي - ترم أول

لينك تحميل الملزمة
https://drive.google.com/file/d/1_HcDz-fQdYFY7cVo3graLigAnqsQCw9V/view?usp=sharing

لينك تليجرام
https://t.me/mrahmedelbashagroup

In This Lesson :
Democritus's idea.  Aristotle's idea.
Boyle's idea.  Dalton's model of the atom.
Thomson's model of the atom.  Rutherford's model of the atom.
Bohr's model of the atom.  The modem atomic theory.
 Democritus's (Greek philosopher) idea:
He imagined the possibility of dividing any piece of matter to smaller parts, then dividing those parts into smaller particles and so on, until we reach to an undividable fragment, he named it an "atom".
• He rejected the former concept of the atom and believed that matter - whatever its nature - is composed of four components, which are water, air, dust and fire.

• It was believed that cheap metals as iron or copper can be changed into precious ones as gold by changing the ratios of these four constituents.

• This illogical idea caused a retard of development in chemistry science for more than thousand years, because the scientists were busy by trying to change cheap metals into precious ones.

The Irish scientist Boyle refused Aristotle's idea about the nature of matter and gave the first definition of the element.

Element
It is a pure simple substance that can't be changed to simpler forms by the traditional chemical methods.


English scientist John Dalton stated the first theory about the atomic structure.
The main postulates of Dalton's atomic theory
 The element is composed of very small particles, which are named atoms.
 The atom is a very minute undividable solid particle.
 Masses of atoms of the same element are similar, but differ from one element to another.
 The compounds are formed by the combination of atoms of different elements in simple numerical ratios.
This last postulate is known as the law of constant proportion which states that each compound always contains the same elements in the same proportion (by mass) no matter how different the method of its preparation.
Example
32 g of sulphur react completely with 48 g of oxygen to form 80 g of sulphur trioxide.
Calculate the mass of sulphur trioxide which is produced from mixing 16 g of sulphur with sufficient amount of oxygen in suitable conditions for the reaction.
Solution

The scientist Thomson carried out many experiments on the electric discharge through gases from which he had discovered the cathode rays.
Discovery of cathode rays (1897):
• It was known that gases don't conduct electricity under normal conditions of pressure and temperature.

• However, gases conduct electricity in a discharge tube whose two poles are connected to an electric source of a suitable high potential difference and under a very low pressure.

• If the potential difference between the two poles of the discharge glass tube increases to around 10000 volts, a stream of invisible rays will be emitted from the cathode (the negative pole), causing a fluorescent glow on hitting the tube wall.
These rays were named "cathode rays".

• It was later known that these rays are composed of minute particles named "electrons".


Properties of cathode rays:
 They consist of very fine negatively charged particles (electrons).
 They move in straight lines (where its speed is lower than the speed of light).
 They have a thermal effect.
 They are affected by both electric and magnetic fields.
 They don't differ either in behavior or in nature if the material of the cathode or the used gas is changed, this is a strong evidence that it is a fundamental constituent of any matter.
In the light of the electrical discharge experiment, Thomson suggested a new atomic model.

The postulate of Thomson's model
He considered the atom as a solid sphere of uniform positive electric charges in which a number of negatively charged electrons is embedded to make the atom electrically neutral.

Rutherford's students Geiger and Marsden performed his famous laboratory experiment.
Rutherford's experiment
The used tools:
• A deep lead box containing a source of alpha particles (a) inside it.
• A metal sheet covered from the inside with a layer of zinc sulphide ZnS.
• A very thin gold foil.
The procedure:
 Alpha particles were allowed to collide the metal sheet, where it was possible to define the location and number of alpha particles by counting the flashes which appeared on the metal sheet.
 A very thin gold foil was placed between the beam of alpha particles and the metal sheet.

• Rutherford recorded his observations and reached the following conclusions:

On the basis of his experiment and from the experiments of other scientists, Rutherford designed his atomic model (the first atomic model on trial basis) as follows:

بالتوفيق
مستر احمد الباشا