Skip to main content

Packing and Packing efficiency in Solids-Class 12 Chemistry

Packing and Packing efficiency in Solids-Class 12 Chemistry

We know that there are 7 crystal systems and 14 types of unit cells that occur in nature. The solid states of the majority of metallic elements, some covalent compounds, and many ionic compounds occur as cubic lattices. There are three types of cubic unit cells within the cubic system.
Let’s pack the three cubic unit cells and the hexagonal unit cell and also determine their packing efficiency. The packing efficiency is the percentage of the total volume occupied by the spheres themselves. We already know that unit cells result from the way the atoms pack together in a crystal lattice.
  1. The simple cubic unit cell: When we arrange the first layer of spheres (imagine particles of the crystals to be identical spheres) in vertical and horizontal rows, then large diamond-shaped spaces are formed. If we place the second layer of spheres directly above the first layer, we obtain the arrangement based on the simple cubic unit cell. The spheres occupy only 52% of the unit cell volume, so 48% of the empty space is left. Hence it is a very inefficient way of packing of particles.
  2. The body-centered cubic unit cell (bcc): If we place the second layer of spheres over the diamond-shaped spaces created, rather than directly above the first layer, than the packing will be more efficient. The third layer is placed on to the diamond-shaped space formed in the second layer. Thus the first and the third layer line up vertically. This arrangement gives body-centered cubic unit cells. This gives the packing efficiency of 68%, which is higher than the simple cubic unit cell arrangement. Several metallic elements, including chromium, iron, and all the elements of Group 1A of Periodic Table, have this arrangement.

CBSE sample papers Class 12 are available, at Takshilalearning.

  1. Face-centered unit cells and Hexagonal unit cells: The spheres are arranged most efficiently in these cells. The spheres in the first layer are arranged such that triangular shaped spaces are formed, which are smaller than the diamond-shaped Then we place the second layer over these spaces. In the second layer, some spaces lie above the spheres in the first layer, whereas some spaces lie above the spaces in the first layer. The third layer can be arranged in either of the two ways-
  • Hexagonal unit cells: If the third layer of spheres is placed on to the spaces of the second layer that lies just above the spheres of the first layer, then the spheres of the third layer are exactly over the spheres in the first layer. The third layer has the same arrangement of spheres as the first layer. Since the structure repeats itself after every two layers, the stacking is described as (abab…) layering pattern, and we get Hexagonal closed packing(hcp) which is based on the hexagonal unit cell. In this, the atoms occupy 74% of space.


Takshila Learning offers live classes and offline classes for School courses. Online/offline classes for Professional courses and Skill development courses are also available. Kindly visit www.takshilalearning.com
Labels:

Comments

Post a Comment

Thank you we will contact ASAP.

Popular posts from this blog

Last Minute Tips to Crack SSC CGL 2019-20 (Tier-I) Exam

Last-Minute Tips to Crack SSC CGL 2019-20 (Tier-I) Exam 1. Don’t read any new topic at the last moment · Try to avoid studying any new topic at the last moment. Just revise what you have already studied. 2. Don’t forget your Admit Card, Photograph and ID Proof · Take a print out of your admit card and original photo identity proof, 1 photo and photocopy of the ID proof. Reach the examination center before time to avoid any last-minute trouble. 3. Maintain your Speed & Accuracy and Maximize your Score · Speed and Accuracy are two important factors to crack any competitive exam. Speed will help in maximizing the attempts while accuracy will ensure that you don’t end up losing marks as the negative marking of 0.5 marks for wrong answers is there. 4. Attempt according to the strategy you followed in the mock tests · Make sure you attempt the easier section first. The exam should be attempted with the same strategy you fol...
4 comments
Read more

Online cbse coaching class for 11 Mathematics

Online cbse Class 11 maths : Online coaching classes for 11 maths  and for other subjects. We are here to solve students problem instantly, So that they can improve himself/herself. One to One Correspondence and Equivalent Sets Suppose the members of the family are dinning and plates are prepared on the table then there is a One to one correspondence between the set of family members and the plates prepared. We will indicate this correspondence by the symbol If each element of a set A is associated with one and only one element of a set B and each element of B is associated with one and only one element of set A, then the sets A and B are said to be in one to one correspondence. If both the sets are finite and if they are in one to one correspondence, it is obvious that they have the same number of elements. If two sets have the same number of elements, they are said to be equivalent sets. Using symbol, we write A B. Between two equivalent sets, a one to one corr...
Post a Comment
Read more

Digital marketing course online and class

Digital marketing course online and class Students and professionals, both are searching for the  digital marketing courses . Generally, the problem occurs in selecting the best  digital marketing course  is – as students and professionals, both have different requirements. Few search for a regular course, some want an additional qualification, or just to improve their skills. On the other hand, every institute has its own pros and cons, learner requirements are not easily matched with the institute’s pattern and regulations. So, they are willing to join some online course as they can learn anytime and anywhere. In India, another challenge is language. Like in North India, Majority of students understands Hindi and they want to do a digital marketing course in Hindi. Finding a good trainer who can teach you in Hindi is very difficult. But this type of course, practical knowledge and getting answers to questions, from a trainer is not so easy. Continue .... ...
Post a Comment
Read more