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Meghna Thapar 5 years, 8 months ago
The law applied in occupied territory by the military authority of the occupying power is called martial law. The law administered by military forces that is invoked by a government in an emergency when the civilian law enforcement agencies are unable to maintain public order and safety is called martial law.
Posted by Ashok Kumar 5 years, 9 months ago
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Meghna Thapar 5 years, 9 months ago
Pretoria is the administrative capital of South Africa. Cape Town is the legislative capital. And Bloemfontein is the judicial capital.
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Meghna Thapar 5 years, 9 months ago
The process of depositing a thin layer of desired metal over a metal object with the help of electric current is called electroplating. The purpose of electroplating is to protect the metal objects from corrosion or to make the metal objects look more attractive. The metal objects are usually electroplated with chromium, tin, nickel, silver, gold or copper objects.
Take 250 ml of distilled water in a clean beaker and dissolve two teaspoon full of copper sulphate in it. This will give us a blue coloured copper solution. Add a few drops of dilute sulphuric acid to copper sulphate solution to make it more conducting. Take a copper plate and a door key made of iron. Clean copper plates and the iron key by rubbing it with sand paper. Now rinse them with water and dry them. Immerse the cleaned copper plate in copper sulphate solution in the beaker. Connect the copper plate to the positive terminal of a battery through a switch. This copper plate becomes the positive terminal. Immerse the cleaned iron key in copper sulphate solution and connect it to the negative terminal of the battery so that it becomes the negative electrode. Allow the current to pass for about 15 minutes. Now remove the electrodes from the solution and observe. We will find that the copper plate has dissolved a little and the iron key has got a reddish layer of copper metal all over its surface. Thus, the iron key has become electroplated with copper. The solution remains unchanged.
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Meghna Thapar 5 years, 9 months ago
- Position of Elements in the Periodic Table:
Periods:
The horizontal rows in the Modern Periodic Table are called periods.
The Modern Periodic Table consists of seven periods which are numbered from 1 to 7.
In each period, a new shell starts filling up. The period number is also the number of shell which starts filling up.
The elements in a period have consecutive atomic numbers, and the number of elements in each period is given below:
- First period contains 2 elements and is called a very short period.
- Second and third periods contain 8 elements and are called as short periods.
- Fourth and fifth periods are long periods and contain 18 elements each.
- Sixth period is the longest and contains 32 elements.
- Seventh period is an incomplete period.
Characteristics:
- The elements in a period have consecutive atomic numbers.
- The no. of elements in period is fixed by the maximum no. of electrons which can be accommodated in various shells.
Groups:
- The vertical columns are called groups and consist of eighteen groups numbered from 1 to 18.
- Elements having the same number of valence electrons are present in the same group.
- Elements present in the same group show the same chemical properties.
- Group 1 contains alkali metals and these elements contain 1 electron in their outermost shell.
- Group 2 contains alkaline earth metals and these elements contain 2 electrons in their outermost shell.
- Groups 3 to 12 have their two outermost shells incomplete.
- Groups 13 to 18 group contain 3 to 8 electrons in their outermost shell.
- Group 18 elements have complete outermost shells. So they are called noble elements or noble gases.
- The element hydrogen has been placed at the top of group 1 because its electronic configuration is similar to alkali metals.
Characteristics:
- The elements in a group do not have consecutive atomic numbers.
- All the elements in a group have similar electronic configurations and show similar properties.
Posted by Gaurav Nawariya 5 years, 9 months ago
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Meghna Thapar 5 years, 9 months ago
- Limitations of Mendeleev’s Periodic Table:
- Hydrogen resembles alkali metals as well as halogens. So, a correct position could not be assigned to hydrogen in the periodic table.
- The position of isotopes could not be explained. Isotopes are atoms of the same element having similar chemical properties but different atomic masses. If the elements are arranged according to atomic masses, the isotopes should be placed in different groups of the periodic table.
- At certain places, an element of higher atomic mass was placed before an element of lower atomic mass. For example: Cobalt (Co = 58.93) was placed before nickel (Ni =58.71).
- Some elements placed in the same sub group had different properties. For example: Manganese is placed with the halogens which are totally different in their properties.
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Nationalism is defined as the identification with one's own nation and support for its interests, especially to the exclusion or detriment of the interests of other nations.
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Universal access of water means that water is a universal solvent to many solutes.
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