Dobereiner’s triads and Newland’s Octaves

Dobereiner’s triads

In since 1820 a German Chemist John Wolfgang Dobereiner arranged similar elements in a group of three.These elements of three groups are known as a Dobereiner triads. Dobereiner said that when three elements in a triads are arranged in increasing order of atomic masses then the relative atomic mass of the middle one is very relative or close to the average of other two elements.

Triad				Triad
1	Cl35.5		1	Li6.9
2	Br79.9	81.2 (Br)	2	Na23	23 (Na)
3	I 126.9		3	K39.1

Newland’s Octaves

 In since 1865 an English Chemist John Newland proposed his law of octaves. He said that if the elements are arranged increasing order of atomic masses then the every eight elements starting from any point will approximately same properties of the first.

Newland’s Octaves
Element	Li	Be	B	C	N	O	F
Atomic masses	7	9	11	12	14	16	19
Element	Na	Mg	Al	Si	P	S	Cl
Atomic masses	23	24	27	28	31	32	35
Element	K	Ca
Atomic masses	39	40

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Compound & Mixture

Compound & Mixture

 Compound

The Substance which is formed by the chemical combination of two or more atom in fixed proportion is called compound.

Examples: C₁₂O₁₁H_22, CO₂ etc.

Explanation:The Compound is pure form of matter.The ratio of an element in a compound is always fixed. The properties of compound is always different from the element forming it. E.g. Sugar (C₁₂O₁₁H₂₂) is made of tasteless element but sugar is sweet. As compound is pure substance therefore showing fixed boiling and melting point and cannot back easily to its constituent element.

Types of Compound

There are two types of compounds and these are

Covalent Compound: The Compound which is formed by the chemical combination of atoms is called covalent compound.

E.g. H₂O, CH₄, CO₂ etc.

Ionic Compound: The Compound which is formed by the chemical combination of ions is called ionic compound.

E.g. Na₂CO₃, Nacl and KCl etc.

Mixture

The substance which is formed by the physical combination of two or more atom not in fixed proportion.

Examples: rocks and stones, flower and soil etc.

Explanation:It is impure substance and can easily back to its original elements. It is not showing fixed boiling and melting point. It has not fixed ratio and proportion. It properties is same as its original elements.

Types of Mixture

There are two types of mixture and these two types of mixture are

Homogeneous Mixture: A mixture in which all the particles have similar look is called homogeneous.

Examples: Air and aqueous solution etc.

Heterogeneous Mixture: A mixture in which all the particles have different look is called heterogeneous mixture.

Examples: Rock and soil etc.

Compound and Mixture Difference 

The Difference b/w them is as follow

Compound	Mixture
Compound is pure substance	Mixture is impure substance
It is formed by chemical combination of atoms	It is formed by Physical combination of atoms.
The properties of compound is different from the element forming it.	The properties of mixture are same as it constituent element.
It cannot easily back to its original elements.	It can easily back to its original elements.
The ratio or proportion of element in a compound is always fixed.	The ratio or proportion of element in a compound is not fixed.
As it is pure substance therefore showing fixed boiling and melting point	As it is impure substance therefore mixture do not show fixed boiling and melting point
It is formed in fixed ratio	It is not formed in fixed ratio.

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Uses of Isotopes

Uses of Isotopes

Isotopes: Isotopes are the atoms of same element with same proton number but different proton number. Radioactive isotopes are the isotopes of radioactive element. Thus Radioactive or radioisotopes are used to understand the mechanism of different reactions. Such as C 14 which is radioactive isotope of carbon is used to label CO₂ i-e how CO₂ can be used to form glucose through photosynthesis.

Archaeological or Geological:Radioactive or radioisotopes are used to estimate the age of fossils. It is based on the half-lives of radioactive isotopes and is called radioactive isotope dating. Such as radiocarbon dating is used to determine the age of old carbon containing material.

Treatment of cancer:Radioactive or radioisotopes are used to treat cancer because it can produce radioactive rays to kill cancerous cells. This process is called radiotherapy. Such as radio isotopes 9 32 and Sr 90 are used to treat skin cancer because it is less penetrating beta radiation.

As tracer in medicines:Radioactive or radioisotopes are used as tracer in medicines to diagnose different diseases. Such as TC technetium is used to monitor the bones growth.

In Power Generation:Radioactive or radioisotopes produces rays if these rays are controlled carefully then we can run or drive turbine through Radioactive or radioisotopes rays to generate electricity. In Pakistan Kanupp (Karachi), Nilore (Islamabad) and Chashma nuclear energy center produces electricity based on this method.

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Nature of Molecule

Nature of Molecule

Onllogy, in this article, is going to explain you about the Molecules and its type. ANd also about the chemical species and also about the free radical.

Molecule

It is defined as "An atom having covalent bond and exist freely in nature is known as molecule". Such as O_2, H₂ etc.

Types of Molecule

There are six types of molecules and these are

1. Monoatomic Molecule
2. Diatomic Molecule
3. Triatomic Molecule
4. Polyatomic Molecule
5. Homo atomic Molecule
6. Hetero atomic Molecule

•  Monoatomic Molecule:A Molecule consisting only one atom is called monoatomic Molecule. Example is all noble gases.
• Diatomic Molecule:A Molecule consisting only two atom is called diatomic Molecule. Example is H_2, Cl₂ etc.
• Triatomic Molecule:A Molecule consisting only three atom is called tri atomic Molecule. Example is H₂O, O₃ etc.
• Polyatomic Molecule:A Molecule consisting only three atom is called Polyatomic Molecule. Example is H_2, Cl₂ etc.
• Homo atomic Molecule: A Molecule consisting only same type of atom is called Homo atomic Molecule. Example is H_2, O₃ etc.
• Hetero atomic Molecule:A Molecule consisting different type of atom is called Hetero atomic Molecule. Example is H_2, Cl₂ etc.

Chemical Species

It is defined as "The species like ions, molecular ion and free radical which form the basis of compound is called chemical species".

Types of chemical species

Ion: Any charge particle is called ion. It has two type. First Cation ion and second anions

• Cation ion: Those ions which has positive charge is called cations and it is formed by the loss of electron.
• Anions: Those ions which has Negative charge is called anions and it is formed by the gain of electron.

Molecular ion: A group of atom having charge is called molecular ion. It can be anions and cations but the number of anions is greater than cations. Such as CH₄, N₂, He+ etc.

Radical or Free radical:An atom or group of atom having unpaired of electron is called radical.

It is represented by putting the dot over the symbol of an element.

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Distribution of electrons in Shells

Distribution of electrons in Shells

In this articles, today, onllogy is going to make you understand about the electrons distributed in different shells. Here, we explain the formula too , by which we calculate the number of electrons in  the shells. so, let's start and have a look on it.

Distribution of electrons in Shells

There are four shells as we all know and the electrons present in these are are different i-e

           1^st shell (K shell)   = 2 electrons

           2^nd shell (L shell) = 8 electrons

           3^rd shell (M shell) = 16 electron

           4^th shell (N shell) = 32 electron

Formula for finding number of electron in a specific shell

The Formula is 2n² where n shows number of shell.

Finding number of electron in shell

•  First Shell

                      The Formula is 2n²

                      2(1)²

                      2(1)

                      2        

  thus first shell accommodates 2 electron.

• Second Shell

                      The Formula is 2n²

                      2(2)²

                      2(4)

                      8          

   thus second shell accommodates 8 electron.

• Third Shell

                      The Formula is 2n²

                      2(3)²

                      2(8)

                      16     

thus third shell accommodates 16 electron.

• Fourth Shell

                      The Formula 2n²

                       2(4)²

                       2(16)

                       32      

thus fourth shell accommodates 32 electron.

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Orbital Speed of artificial satellite

Orbital Speed of artificial satellite

Satellite: 

Any object that revolves around another object or planet is called satellite of that object or planet.

The satellites are of two types

1.    Natural satellite

2.    Artificial satellite

1 . Natural satellite:  A satellite which naturally revolves around the planets or starts are called natural satellite. Such as moon, sun etc.

2 . Artificial satellite:  A satellite which is sent by the scientist to revolve around the earth is called artificial satellite.

Orbital Speed of artificial satellite

Expression for the orbital speed:

Suppose a satellite is revolving around the earth at height h from the surface of the earth. Here the mass of earth is M, the mass of satellite is m and the speed of satellite is v and the distance b/w the centre of the earth and the satellite is equal to R+h.  Since  satellite is revolving around the earth in circular path. So centripetal force is

                 F_c  = mV² / R+h ------- eqn(1)

This centripetal force is provided by the gravitational force of earth. so

F_c  = GMm / (R+h) ²  --------- eqn(2)

Combining both equations we get. So 

This equation represents the orbital speed of the artificial satellite. However if the height of the satellite from the earth is not very large so h is neglected and R+h becomes R and V becomes the Vorbital = Vorb

           

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Variations of Gravity (g) with altitude

Variations of Gravity (g) with altitude

Suppose a body of mass m is placed at the height h from the surface of earth. Here the distance b/w them is R + h where M is the mass of earth. Suppose g_h is the gravitational acceleration at this position. So gravitational force is

F = GMm / (R+h) ² ------ eqn (1)

as we know that the force is equal to the weight of body. That is

F = W = mg   ------ eqn (2)

From both eqns we get

g_h = GM / (R+h) ² --------- eqn(3)

As the mass of earth is

                              M = gR² / G     

              ••►  GM =  gR²  put this in eqn 3. So

g_h = gR²  / (R+h) ²

This shows that the value of g decreases as h increases. Hence the value of g decreases as altitude increases.

                                                                   

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