There are many great resources to learn assembly but none of them seem to go into much detail on how assembly mnemonics get turned into raw binary instructions.
The mnemonics aren't 'turned in' to raw binary instructions, they are the raw binary instructions. It is a human readable representation of the actual hex bytes that are encoding the instructions of the (first generation language) machine code. We typically talk about these bytes by their mnemonics for clarity.
This is unlike assembly (so, second generation language such as gas or masm) or C (third generation language). Both assembly and higher generation languages are source files with a character encoding (such as UTF-8) that encodes the letters of the source code. In the case of assembly, it needs to be assembled to raw x86 bytes. The raw bytes can be disassembled by IDA into a readable form; it's called disassembly because it's presenting the mnemonic representation encoded in a character set like UTF-8 and displayed to the screen (which resembles an assembly language (a second generation language) that would be assembled to machine code -- in this case it's obviously not going to be assembled and isn't really an assembly language on it's own -- it's showing you what the assembly that was compiled to the machine code would have been).
x86 encoding looks like this (I created a diagram):
By the same token, CIL bytecode is a 1st generation language because the opcodes run directly on the virtual machine -- a virtual CPU. This means that the CIL bytecode does not need to be assembled or compiled from a source file with a source character set.
ilasm shows a disassembled, mnemonic form of this bytecode.