Hello students, how are you? Welcome to my YouTube channel Pankaj Pichis Gulhanti. Today we will study the first important topic of BSc 6th Sam, Solid State, Nanophysics Unit 1 which is Difference between Crystalline and Amorphous Solids. The matter is discussed in three states, which are solids, liquid and gases. Solids have definite shapes, while the other two forms of matter, i.e. liquid and gases, do not have definite shapes. We can further divide solids into two categories namely crystalline solids and amorphous solids. Amorphous solids are also called glassy solids. So students today we will study the difference between crystalline and amorphous solids. Let's see what is the difference between them. The first difference between crystalline solids and amorphous solids is that the atoms in crystalline solids are regular. While in amorphous solids the arrangement of atoms is not regular. This is the difference between crystalline solids and amorphous solids. In crystalline solids atoms are arranged in regular way. In amorphous solids the atoms are not arranged in regular way. So this is the first difference you will write in the exam. What is the second difference? Because the atoms in crystalline solids are arranged regularly and in definite pattern so the order of atoms is long range order. Means they are arranged regularly from far to near. In crystalline solids, atoms are arranged from far to near. Whereas in amorphous solids, it is not like that. In these, the order of atoms is short range. So students, this is the difference between second and third. They possess long range order of atoms. And here you will write in Morpheus words, They possess short range order of atoms. They possess long range order of atoms. They possess short range order of atoms. The third point is that the melting point of crystalline solids is fixed. The melting point is sharp. A particular crystalline solid melts at a particular temperature. Whereas amorphous solids have a melting point that is not sharp. They melt at a temperature above the range. They do not have a fixed temperature at which they will melt. So the third difference is that these solids have sharp melting points. These do not have sharp melting point. What is the fourth difference? Crystalline solids are anisotropic in nature. What is the meaning of anisotropic? Their physical properties like mechanical properties, electrical properties, optical properties, their values are different in different directions. So students, this is called anisotropic structure. What is the fifth students, amorphous solids are isotropic in nature means their physical properties like mechanical, electrical, optical their values are same in different directions in every direction their physical properties will be same that's why they are called isotropic solids Their physical properties will be different in different directions. That is why they are called anisotropic. So, these are the four different students. They are anisotropic in nature. That is the physical properties like mechanical, electrical, optical have different values in different directions. In this you will write they are isotropic in nature. That is anisotropic and this is isotropic. That is the physical properties like mechanical, electrical, optical have same values in different directions. Physical properties will be different in different directions. Their physical properties will be same in different directions. This is anisotropic and this is isotropic. So, these are four differences. We will study next two differences in the next section. So today we have seen four differences between crystalline solids and amorphous solids. As you can see in the figure, crystalline solids have regular arrangement, atoms have no regular arrangement in amorphous solids. In the second point of atoms, we saw that the order of atoms in crystalline solids is long range order. Means the atoms are arranged in a long range. And in the second point of amorphous solids, the order of atoms is short range order. Third difference is that, The melting point of crystalline solids is sharp whereas the melting point of amorphous solids is not sharp. Fourth point we saw that crystalline solids are anisotropic which means their physical properties are different in different directions. And amorphous solids are isotropic which means their physical properties are same in different directions. Let's see the other two differences. Students... Because atoms are arranged regularly, the melting point of atoms is sharp, so we keep them in the category of two solids. Crystalline solids are treated as two solids. This is the fifth point of crystalline solids. Because atoms are not arranged regularly, they are not arranged in a definite pattern, their melting point is not sharp. Short range of... Short range order of atoms is there, that's why we don't consider them as true solids. These are not true solids. And in the last point, you will write their examples. The best examples of crystalline solids are mica, diamond, sodium chloride, NaCl, and the best examples of this are morphosolids, glass, rubber, plastic. In these, the atoms are not regularly arranged, they do not have a sharp melting point, they are isotropic. and in short range order of atoms is there so students this was the difference between crystalline solids and amorphous solids which can be asked to you with compulsory question with two marks or with any long question this part can be asked to you so students I hope you have understood today's lecture see you in next video thank you so much