If I may...Thunder is 'sound' therefore a facet of air thru which the sound travels. Lightning is a facet of 'fire' albeit a much more powerful version of it (technically) Shadow and light are simply yin and yang. Not 'quite' elements as light is a facet of fire ( the suns nuclear fire which 'creates' the light to begin with) Shadow is the 'lack' of light and not truly an 'element'. You cannot have one without the other. Metal is a 'part' of earth not separate from it.
( these of course are 'opinions' before someone goes nuts about it. Things I learned thru my decades of practice)
Uh earthgirl..Heat can exist 'independently' of cold, take our sun for instance there is no 'lack' of cold there. The sun exists thru the nuclear fission of the elements that make it up. Cold also can exist independently, out in the vastness of space there is a bone-chilling cold that exists and will always exist. Heat may come and go but there will always be cold in space. Tones and sounds are shades of grey.There are sounds that we also do not 'hear' such as ultrasonic that which dogs hear and we don't...just like light broken down into it's spectrum is a many hued rainbow including those which our eyes 'cannot' see such as the infrared and the ultraviolet.