Common name of CH2Cl2 [closed]

Question

My book says geminal dihalide or alkylidene halide is the common name for dihaloalkanes where both halogen atoms(if of same element) are bonded to the same carbon atom and alkylene dihalide if 2 halogens of same element bonded to adjacent Carbon atoms.

But in a list of examples in the same book, $\ce{CH2Cl2}$ is named as Methylene Chloride. Shouldn't it be Methylidene Chloride?

Here is text from NCERT Chemistry Class 12 Part 2 Chapter 10:

The dihaloalkanes having the same type of halogen atoms are named as alkylidene or alkylene dihalides. The dihalo-compounds having both the halogen atoms are further classified as geminal halides or gem-dihalides when both the halogen atoms are present on the same carbon atom of the chain and vicinal halides or vic-dihalides when halogen atoms are present on adjacent carbon atoms. In common name system, gem-dihalides are named as alkylidene halides and vic-dihalides are named as alkylene dihalides. In IUPAC system, they are named as dihaloalkanes.

Answer 1

No ! $\ce{C2H2}$ (from $4$th line) is named ethyne. It has also a more usual and older name : acetylene. But today the author wants to discuss about $\ce{CH2Cl2}$

$\ce{CH2Cl2}$ is usually called dichloromethane. But it has an older name : methylene chloride, which can be justified by stating that $\ce{CH2Cl2}$ looks as it was a chloride (and even a dichloride) of the group $\ce{CH2}$ who was earlier called methylene. This nomenclature was coming from before IUPAC (created $1918$). Before $1918$, all compounds of chlorine were called "chlorides".

In the $19$th century, the alkanes had an end in -ane (like today). With one $\ce{H}$ removed, the molecule becomes a radical in -yl (like today). But with two $\ce{H}$ lost, it becomes -ene or -ylene. Today, we specify on which atom the $\ce{H}$ atoms have been removed, in molecules containing $2$ or more Carbon atoms. Strangely enough, removing $3$ $\ce{H}$ atoms from an alkane gave the group $\ce{CH}$ which was sometimes called form- (from formic acid).

Let's go back to all chloro- derivates of methane: Removing $1$ or several $\ce{H}$ atoms from methane $\ce{CH4}$ yields first the radical $\ce{CH3}$ which was and is called methyl; then $\ce{CH2}$ is obtained which was called methylene. So, before IUPAC, $\ce{CH3Cl}$ was called methyl chloride (today chloromethane), and $\ce{CH2Cl2}$ was called methylene chloride (today dichloromethane). Furthermore, trichloromethane $\ce{CHCl3}$ was called "chloroform", and tetrachloromethane $\ce{CCl4}$ was called "carbon tetrachloride".