The understandable notes- Carbon and its compounds, Class 10, Part-5

Isomerism 

The phenomenon in which compounds have the same molecular formula but differ only in the arrangement of atoms or functional group is called isomerism. A carbon compound having a same molecular formula can exist in different ways.

( Vaise to ye topic nomenclature se pehle tha par tab samajh nahi aata. To dekho humne ye dekha hai ki carbon compound kai tarike se bond banate hai. Ab inme aisa bhi ek tarika hai ki molecular formula to same rahe par compound alag ho. Aur ye mai hawa hawa mai nahi bta raha hu jis tarah se atom arranged hai is par compound ki dono chemical aur physical properties depend krti hai. Tumhe bas samajhna hai ki isomerism hota kya hai iske jyada deep mai ja e ki jarurat nahi hai. Bilkul basic sa hai teen char compound ke through samjh dunga.)

See the compound with molecular formula 

This can exist in several ways like

Pentane
OR

Or

2,2 dimethyl propane

In the above three compound, you can see that all the compounds have same molecular formula but the way in their atoms are arranged is different.

( Ab dekho pentane mao 5 carbon atom hote hai aur 12 hydrogen atom hote hai. Ab maine inhe teen tariko se represent kar diya. Pentane teen tariko se hi represent ho sakta hai. Iske alawa kaise bhi karlo wo inhi teeno mai se koi nikal jayega. To dekho ab butane aur hexane ke isomers practice karo aur google baba se answer check kar lena.  )

There is also one more way to represent pentane that is in cyclic form. But in cyclopentane the molecular formula got changes so we didn't consider it as isomer of pentane.

Also carbon compound can exist as ring, the structure of cyclohexane is given below

Now complete the structure by adding hydrogen to the molecule.

Now the structure of a special compound is given below.

This is the structure of benzene. Learn it beacuse it is very important in organic chemistry. C6H6 is the molecular formula for benzene.

( To dekho cyclic compounds to tumhare syllabus mai nahi hai lekin bemzene ka structure yaad kr lo. Ye kafi important hai aur kai baar puch liya jata hai.)

Homologous Series

A homologous series is a group of organic compounds that share the same general formula, have similar chemical properties, and exhibit a gradual change in physical properties due to a consistent difference in their molecular structure.

( Homologous series organic compounds ki ek aisi series hoti hai jinka general formula same hota hai. Har Homologous series ka ek general number hota hai aur compounds ki property ek dusre se kafi same hoti hai. Lekin physical propertied differ krti hai molecular structures  alag hone ke karan.)

Characteristics of a Homologous Series:

1. Same General Formula: Compounds in a series follow a general formula, e.g., alkanes (CₙH₂ₙ₊₂), alkenes (CₙH₂ₙ), etc.

( Yaar dekho inka general formula same hota hai. Jaise ki alkanes ka general formula CnH2n+2 hota hai. Ab sare alkanes mai ye formula hi rahega bas number change honge. Yani ki agar carbon ki value 7 hai to hydrogen 16 honge. Ye har alkane par valid hai. Yeh characteristic hai Homologous Series ka.)

2. Gradation in Physical Properties: Physical properties like boiling point, melting point, and density gradually change as molecular size increases.

( Ab dekho Homologous Series mai physical properties series mai badhne ke karan badh jati hai. Yaar dekho methane mai ek carbon hai aur ethane mai 2. To boiling point 2 carbon ka jyada hoga. Ye to suna hi hoga ki ekta mai ji bal hai. Bas yehi baat Homologous Series mai apply hoti hai. Jo jitna bada hota hai uski physical properties utni hi strong hoti hai.)

3. Similar Chemical Properties: All members have the same functional group, giving them similar reactivity.

( Yaar dekho sirf alkanes hi nahi, balki har functional group ki ek Homologous Series hoti hai. Jaise ki methanoic acid, ethanoic acid,  propanoic acid vagera. Ab inka structure almost same hota hai isi liye i ki chemical properties  same hoti hai par bilkul same nahi hoti.)

4. Difference of CH₂ Group: Successive members differ by a -CH₂- unit.

 (  Ye kaafi important hai ki Homologous Series mai jo agla member hoga vo pichle se ek CH2 group jyada carry krega. Aur ye har series par valid hai chahe for koi functional group ho ya koi functional group na ho. Jaise ki ethanal mai se agar ek ch2 group ko kam kr denge to methanal ban jayega. Chalo ye part to khatam agle part mai chemical properties padhni hai carbon compounds ki.)