chemistry crossword

3. positively charged particle in the nucleus of an atom
6. system an experiment in which all reactants and all products of a chemical reaction are accounted for
7. reactions reaction that takes place when two or more substances react to form new substances
9. reaction that occurs when oxygen reacts with a substance to form a new substance and give off energy
10. compound pure substance formed when at least one metal and one non-metal combine
12. substance that helps a chemical reaction to proceed more quickly
14. element that has both metallic and non-metallic properties
15. atom that has become electrically charged because it has lost or gained electrons; a positive ion is an atom that has lost one or more electrons;a negative ion is an atom that has gained one or more electrons
18. catalyst involved in chemical reactions in living things
19. neutral particle in the nucleus of an atom
20. number the sum of the number of protons and neutrons in an atom
21. number number of protons in the nucleus of one atom of an element

1. the smallest part of an element that is representative of that element; a neutral particle made up of a nucleus containing protons and neutrons, and in which the number of electrons equals the number of protons
2. ability of a substance to conduct electricity or heat
4. compound pure substance formed when non-metals combine
5. table table in which the elements are organized by their physical and chemical properties
8. dull, brittle element that does not conduct electricity
11. group 17 elements in the periodic table;the most reactive non-metals
13. metals group 1 elements in the periodic table, not including hydrogen; the most reactive of the metals
16. system an experiment in which one or more products of a chemical reaction can escape
17. monoxide (CO(g))colourless, odourless gas;produced by incomplete combustion of chemicals containing carbon (e.g. hydrocarbons); major source: motor vehicles