Across
1
Compound containing oxygen
5
Nerve cell in the brain
6
Unit of force
8
Our home planet
11
Fourth state of matter
12
Second lightest element
Down
2
Particle of light
3
Naturally occurring inorganic solid
4
Curved glass that refracts light
7
Gas essential for breathing
9
Reddish electrical conductor
10
Center of an atom or cell