Are there things of the Ghayb which are not composed of atoms?

Answer

Things of the Ghayb(Unseen Realm) consist of material and immaterial creations. No one knows the actual constitution of purely spiritual creations such as the arwaah (souls) and numerous other items and species of Allah's creation.

Jannat and Jahannum are both physical abodes of a vastly superior kind of physical material than what we can ever imagine or dream of. We are physical beings together with spiritual souls which give us our personalities. Allah Ta'ala will reward us with a physical Jannat. All the pleasures and comforts in Jannat will be of a physical nature, but infinitely superior to what we have, know and see on earth.