Periodic Puzzle

3. A small particle in the nucleus of an atom, with no electrical charge.
6. An element in group 18 of the periodic table.
8. A particle given off during radioactive decay that consists of two protons and two neutrons.
9. An element that has some characteristics of both metals and nonmetals.
10. The process in which radioactive elements break down, releasing fast-moving particles and energy.
11. A characteristic of a pure substance that can be observed without changing it into another substance.
12. Electromagnetic waves with the shortest wavelengths and highest frequencies.
13. The spontaneous emission of radiation by an unstable atomic nucleus.
14. A one or two letter representation of an element.
18. Small, positively charged particles that are found in the nucleus of an atom.
20. The ease and speed in which an element combines or reacts with other elements and compounds.

1. A horizontal row of elements in the periodic table.
2. A characteristic of a substance that describes it's ability to change into different substances.
4. A substance that cannot be broken down into any other substances by chemical or physical means.
5. An element that lacks most of the properties of a metal.
7. The nonmetals in group 17 that includes fluorine, chlorine, bromine, and iodine.
15. A tiny, negatively charged particle that moves around the outside of the nucleus of an atom.
16. The basic particle in which all elements are made.
17. A fast-moving electron that is given off as nuclear radiation.
19. The average mass of all the isotopes of an element.