1) The name of the star system otherwise known as "our galaxy", or the "local galaxy" and
2) The name of the "way" (in the sense of "path" or "street") or milky looking, blurry region that extends completely around the sky.
The atoms make their presence known as absorption lines in stellar spectra, as well as by producing their own (emission) spectra.
The dust can be seen to obscure objects behind it, and more subtly, to "redden" the light of stars seen through it. This reddening arises from the same phenomenon which causes the reddening of the sun as it sets, and which is responsible for the blue of the sky.
Cold hydrogen gas (isolated atoms) produces light of wavelength 21 cm. The atomic transition responsible for this is the flipping of the orientation of the nucleus (which is a magnet) in the magnetic field of the orbiting electron. Because this flipping requires such a small amount of energy compared to that needed to produce visible light, it can happen at the very low temperature of interstellar space; and because so little energy is involved, the wavelength is very long compared to visible light. The Doppler shift of this 21 cm radiation allows the identification of spiral arms of the galaxy.
We suspect we are in a spiral because so many other galaxies are spirals. But the evidence that we are actually a spiral galaxy is indirect; we get our evidence from this 21 cm data, and from corresponding visible light (from stars) Doppler shift data.
The spectral evidence for interstellar molecules ("chemistry") is surprising and intriguing. Surprising because the interstellar medium is so tenuous that the collisions between atoms (needed before the atoms can join together into molecules) are so rare. Intriguing because chemistry is the precursor to biology, and if there is interstellar chemistry, perhaps there could be interstellar biology.