chemistry crossword

4. general term for a specific isotope of an element (3)
6. a logical approach to solving problems by observing and collecting data, formulating and testing hypothesis and formulating theories supported by data (2)
9. emission from a metal when light shines on it (4)
11. a testable statement (2)
12. distance between corresponding points on adjacent waves (4)
15. organizes elements by their chemical properties (1)
17. anything that has mass or takes up space (1)
18. 6.022x10^23 km (3)

1. measure on gravitational pull on matter (2)
2. has a fixed composition (1)
3. states matter cannot be created nor destroyed during chemical reactions or physical changes (3)
5. 6.5x10^23 km (2)
7. atoms of the same element but different masses (3)
8. equals the value experimental-value accepted divided by the value accepted x100 (2)
10. poor conductor of heat and electricity (1)
13. building blocks of matter (1)
14. contains protons and electrons (3)
16. group 18 elements (4)