Across
1
Compound containing oxygen
4
Positive particle in nucleus
6
Second lightest element
7
Center of an atom or cell
11
Fourth state of matter
12
Precious yellow metallic element
Down
2
Gas form of a liquid
3
Gas essential for breathing
5
Curved glass that refracts light
8
Our home planet
9
Element found in all living things
10
Naturally occurring inorganic solid