Periodic Puzzle

6. A fast-moving electron that is given off as nuclear radiation.
9. The process in which radioactive elements break down, releasing fast-moving particles and energy.
12. A horizontal row of elements in the periodic table.
13. Electromagnetic waves with the shortest wavelengths and highest frequencies.
15. The ease and speed in which an element combines or reacts with other elements and compounds.
17. An element that lacks most of the properties of a metal.
19. An element in group 18 of the periodic table.
20. A substance that cannot be broken down into any other substances by chemical or physical means.

1. A particle given off during radioactive decay that consists of two protons and two neutrons.
2. The nonmetals in group 17 that includes fluorine, chlorine, bromine, and iodine.
3. A characteristic of a substance that describes it's ability to change into different substances.
4. A one or two letter representation of an element.
5. Small, positively charged particles that are found in the nucleus of an atom.
7. A characteristic of a pure substance that can be observed without changing it into another substance.
8. The spontaneous emission of radiation by an unstable atomic nucleus.
10. An element that has some characteristics of both metals and nonmetals.
11. The average mass of all the isotopes of an element.
14. The basic particle in which all elements are made.
16. A tiny, negatively charged particle that moves around the outside of the nucleus of an atom.
18. A small particle in the nucleus of an atom, with no electrical charge.