Across
1
Mass per unit volume
4
Center of an atom or cell
5
Hottest planet in solar system
7
Positive particle in nucleus
9
Path of a planet around the sun
10
Precious yellow metallic element
11
Smallest unit of an element
12
Solid with repeating atomic pattern
Down
2
Biological catalyst
3
Unit of force
4
Nerve cell in the brain
6
Unit of electric potential
7
Fourth state of matter
8
Group of similar cells
13
Glass that splits light into spectrum