Across
- 4. unknown
- 5. outer
- 6. light
- 9. unpaired
- 10. positive
- 11. sub-shells
- 14. shortcut
- 16. valence dots
- 17. lowest energy
- 18. color lines
- 19. energy level
- 20. possibilities
Down
- 1. build
- 2. higher energy
- 3. shape
- 7. arrows
- 8. opposite
- 12. charge
- 13. two forms
- 15. negative