Why Solids are rigid and incompressible ?

Matter is anything that has a mass and occupy space . Ice  , pen , pencil ,dog , etc are examples of matter because they have some mass and they occupy space .

There are basically three states of matter ,

●Solid 

●Liquid

●Gas

Solid 

Solid is defined as rigid and incompressible state of matter . 

Now the question is ,

why Solids are rigid and incompressible ?

To answer this question , let's understand the properties of solids . 

1.Solids have large intermolecular force of attraction . Intermolecular force is the force of attraction between to adjacent Molecules .  Higher the intermolecular force , more tightly they will attract each other and less movement of Molecules will occur .

2.Intermolecular distance in Solid is very less . Intermolecular distance is the distance between two adjacent molecules . Less the distance more will the intermolecular force of attraction . Intermolecular force is inversely proportional to intermolecular distance .

3.They have definite shape and volume . It simply means solid will not change it' s shape on the basis of container .  For example , take some water and filled the container , it will change the shape according to container and take a rod an place in different container solid will not gonna change its shape . 

So this are some basic and useful property of solids .

Coming to the question ,

Solids are rigid because the intermolecular distance between the Molecules of solid is very less .Due to this , they are not allow to move randomly . They vibrate about their own axis . Therefore , solids are rigid in nature .

Solids are incompressible because the empty space between the molecules in a solid is very less . More the empty space , more will the compressibilty . Therefore Solids are incompressible in nature .

Why some solids are hard and some solids are soft .

Hardness and softness of a solid depends on the types of bonds present in solid and how strong that bond is . 

Transition metals have large number of unpaired electron . They can form large number of Covalent as well as metallic bonds with other atoms . Due to this Solids of transition metal are hard in nature . Silver , gold , copper , aluminum , ferrous are some examples of hard solid .

Metals with no unpaired electrons are soft  in nature due to absence of unpaired electrons . They can't form Covalent bond and that's why they are soft in nature  . Zinc Chloride is an example of soft solid because in this complex zinc has no unpaired electrons .