Across
1
Chemical element in table salt
4
Center of an atom or cell
5
Particle of light
6
Substance with pH above 7
12
Biological catalyst
13
Molten rock beneath Earth surface
Down
2
Group of similar cells
3
Path of a planet around the sun
7
Our home planet
8
Gas form of a liquid
9
Second lightest element
10
Unit of energy
11
Natural satellite of Earth