Sigma and Pi bonds

 sigma and pi bonds are two types  of covalent bond. They differ each other on the mode of overlapping of atomic orbitals - head to head overlapping or side wise overlapping. First kind of overlapping gives sigma bond while second kind of overlapping gives pi bond.

 Electron density concentrates between two nuclei. It can shield internuclear repulsion effectively. Then there is  greater extent of overlapping of atomic orbitals. That makes sigma bond stronger.

 Where as electron concentrates above and below the internuclear axis. So, it can not shield internuclear repulsion effectively. As a result there is lesser extent of overlapping on pi bond which makes pi bond weaker than sigma bond

Click  here to watch   video of sigma bond and pi bond.

memory trick for atomic weight

 

Here are some technique to memorize name of elements and atomic weight of elements. It is specially concerned for the elements having atomic number between 20 to 30. First of all, lets discuss how to remember name and symbol of elements from atomic number 21 to 30.

सचिन,तेन्दुल्कर,बिराट कोली,क्रिश गेल,मे , फिर,कोही,नयाँ, सेन्चुरी, जमाएगा        

Now I'm going to tell you three rules to remember atomic weight. they are 

i) 2n rule,

ii) (2n+1) rule  and

 iii) (2n +x) rule 

2n and  (2n+1) rule

First two  rules are applicable for the elements having atomic number up to 20. 2n rule is applicable for even atomic number and (2n+1)  rule is applicable for odd atomic number. However, Be follows (2n+1) rule, nitrogen follows 2n rule regardless the atomic no. Atomic weight of Cl is 35.5 and that of Ar is 40. 

even atomic no = 2n rule 

odd atomic no = 2n +1 rule

Exceptions  :   H, Be, N, Cl  & Ar

(2n+x) rule 

It  is applicable to memorize atomic weight of elements from Sc to Zn. It is easiest trick that gives whole number values only. where,

Atomic wt = 2n + x                                              

where, n  = atomic number  of element and   

x = Three वटा  45 three 55          

That is, x = 3, 4,5,4,5,4,5, 3,5,5  

Common names of organic compounds

 Though IUPAC name is more systematic and unambiguous, common name  or trivial name is widely used on organic chemistry as well as at the industries. vinyl chloride, ethyl chloride, benzyl chloride, benzal dichloride, benzotrichloride, benzoyl chloride etc are some common names.

Click here: list of common name of organic compound 

ore and mineral

 Different compounds- ores and minerals are more pronounced by their common names rather than IUPAC name. NaCl (Sodium chloride) is commonly called rock salt , table salt as well as common salt. Zinc carbonate is called calamine.

Click here: list of ore and mineral with their common name.