Across
1
Unit of energy
3
Smallest unit of an element
4
Center of an atom or cell
5
Icy body with a tail near the sun
7
Magnetic metallic element
11
Particle of light
Down
2
Chemical element in table salt
4
Nerve cell in the brain
6
Positive particle in nucleus
8
Second lightest element
9
Group of similar cells
10
Gas essential for breathing