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The great variety of matter in the universe depends on the fitting together of 92 kinds of atoms to form all manner of structures. These 92 different kinds of atoms consist of 92 different nucleii with corresponding swarms of electrons. We have just mentioned that on sufficient heating the molecules of matter get broken up into the constituent atoms. The question next arises as to what happens when an atom or atoms are continuously heated to a very high temperature. The temperature within the interior or certain stars is very high, the highest temperature estimated by Eddington being about four crore degree Centigrade. What would be the state of atoms inside these stars? At these high temperatures the atoms begin to lose their outer electrons, i.e., the electrons which compose the body of the atom begin to separate from the atom. Such atoms, in the language of science, are called 'ionised' atoms, and the process of separation of the electrons from the atom is called 'ionisation'. In some case it happens that atoms lose entirely their rings of electrons,
the atoms are then called 'stripped' atoms." 38. (a) धातुओं में रहे हुए परमाणुओं के बीच जो पारस्परिक बन्धन है, उसे विस्तार से समझने के
fag TETEHT JAG UT Satish K. Gupta, op.cit. p. 1225."Metallic Bonds A metallic bond is force, which binds the atoms of a metal with one another. The metallic bonding is explained on electron gas model. According to this model; in metallic atoms, electrons are loosely held by the nucleus due to low ionisation potential. The valence electron of an atom can leave its positive ionic core (nucleus and inner orbital electrons) and enter into the influence of the ionic core of another atom. This collection of mobile free electrons around the ionic core is found to be more stable than the neutral atoms. The force between the mobile valence electrons and positive ionic cores holds the metallic atoms together, which is known as metallic bond. Properties: 1. Metallic compounds are usually solids. However, mercury
is the example of a liquid metallic compound. 2. Metallic compounds are usually crystalline in nature.
They are good conductors in solid state. 4. Metallic bonds are weak bonds.
Metallic bonds are non-directional. 6. Metallic compounds are opaque to light. This is because,
light energy falling on them is absorbed by mobile electrons.
TM
451 37067 - fogtok, 2003
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