Periodic Puzzle

3. The basic particle in which all elements are made.
4. Electromagnetic waves with the shortest wavelengths and highest frequencies.
6. The process in which radioactive elements break down, releasing fast-moving particles and energy.
8. Small, positively charged particles that are found in the nucleus of an atom.
9. A horizontal row of elements in the periodic table.
10. A substance that cannot be broken down into any other substances by chemical or physical means.
11. A characteristic of a pure substance that can be observed without changing it into another substance.
12. A one or two letter representation of an element.
14. A small particle in the nucleus of an atom, with no electrical charge.
15. The nonmetals in group 17 that includes fluorine, chlorine, bromine, and iodine.
17. An element in group 18 of the periodic table.
19. The spontaneous emission of radiation by an unstable atomic nucleus.

1. The average mass of all the isotopes of an element.
2. A fast-moving electron that is given off as nuclear radiation.
5. A particle given off during radioactive decay that consists of two protons and two neutrons.
7. A characteristic of a substance that describes it's ability to change into different substances.
13. An element that has some characteristics of both metals and nonmetals.
14. An element that lacks most of the properties of a metal.
16. A tiny, negatively charged particle that moves around the outside of the nucleus of an atom.
18. The ease and speed in which an element combines or reacts with other elements and compounds.