Crossword

3. these elements react to form positive ions
6. scientist who devised the modern periodic table
8. elements with similar properties are arranged in these
10. the discovery of these made it possible to explain why the order of elements based on atomic weights was not always correct
11. these are non-metals with seven electrons in their outer shell
12. a more reactive halogen can do this to a less reactive halogen from an aqueous solution of its salt

1. these were left by Mendeleev for undiscovered elements
2. these occur down groups and depend on distinctive properties of elements
4. the arrangement of these in its atoms determines an elements position in the table
5. these metals are reactive as they have a single electron in their outer shell
7. these gases are unreactive as they have a stable arrangement of electrons
9. this number determines the order of elements in the periodic table