chemistry notes for class 10 chapter 12 hydrogen

chemistry notes for class 10 chapter 2 hydrogen

class 10 chapter

Chemistry New Shams Notes

Q.1: What are hydrocarbons? Explain with examples.

Ans: Hydrocarbons:

“The compounds of carbon and hydrogenare called hydrocarbons.” Classification of hydrocarbons:

Hydrocarbons are classified into two main groups:

i.  Saturated hydrocarbons (alkanes)

ii. Unsaturated hydrocarbons (alkenes and alkynes)

i. Saturated hydrocarbons:

“The hydrocarbons which contain all carbon-carbon single bonds are called saturated hydrocarbons or alkanes.”

General formula:

They have the general formula of CnH2n+2, where n is the number of carbon atoms.

Examples:

Methane (CH4), Ethane (C2H6), propane (C3H8) and butane (C41110 etc. are the examples of saturated hydrocarbons.

ii.       Unsaturated hydrocarbons:

“The hydrocarbons containing at least one carbon-carbon double or triple bond are called unsaturated hydrocarbons.”

They are further classified to:

a. Alkenes:

“The hydrocarbons which contain at least one carbon-carbon double bond are called alkenes.”

General formula:

They have the general formula of CnH2n, where n is the number of carbon atoms.

Examples:

Ethene (C2H4), propene (C3H6), butene (C4H8) and pentene (C6H1o) are examples of alkenes.

10 CLASS NOTES

Q.2: Write a short note on alkanes?

Ans: Alkanes:

“The saturated hydrocarbons containing all carbon-carbon or carbon to hydrogen single bonds are called alkanes or paraffin.”

Reason for calling paraffin:

Paraffin is a Latin word meaning “little affinity”. Since alkanes contain C-C and C-H single bonds, therefore they have a little affinity towards chemical reactions that is why they are called paraffin.

Reason of calling saturated hydrocarbons:

Since in alkanes each carbon atom is bonded with four other atoms therefore no further atom can be added to alkanes. Hence, they are called saturated hydrocarbons.

General formula:

The general formula of alkanes is CnH2n+2 where n is the number of carbon atoms e.g. if n=1 then the formula will be CH4, which is called methane. Similarly if n=2 then the formula will be C2H6 called ethane etc. Examples:

The name of the first ten alkanes along with their physical states, melting point, and boiling points are given in the table below:

chemistry notes

Naming the longest chain:

Name the longest chain e.g propane for 3, butane for 4 carbon atoms etc.

It is called the base name or parent name of the compound. 

Example:

For example, the parent name of the above example is hexane.

iv.  Naming the branch:

Name each branch (substituent) attached to the longest chain and give its location by the number of the carbon atom to which it is attached. A hyphen is used between the number and name of the branch, and comma (,) is used between number and number.

Example:                                                                                                                                                                  •

For example, in the above example, 3-methyl is the position of the branch.

v.    Writing the full name:

The parent name is written at the end, after mentioning the position of the substituent.

Example:

For example, the name of the above compound is 3methyl hexane.

vi.  Naming two or more identical branches:

When two or more identical branches are present then use prefixes di, tri, tetra, etc. A comma is used to separate the position numbers. 

Example:  

class 10 chapter 12 hydrogen

iii. Numbering the branches on same carbon:

When two branches are present on the same carbon uses the number of that carbon twice.

Example:

For example, in the above example two methyl groups are present on the same carbon therefore their position is mentioned as 2,2.


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