Chemistry crossword

3. the amount of heat energy required to raise the temperature of a unit mass of that substance by one degree Celsius
5. The horizontal rows of the periodic table
7. ions that are positively charged
11. Chemical reactions that release energy
12. an atom or molecule with a net electric charge due to the loss or gain of one or more electrons
15. the eight-electron arrangement in the outer electron shell of the noble-gas atoms
16. ions that are negatively charged
17. the exchange of "thermal” energy due to a temperature difference
18. the number of a chemical element in the periodic system, whereby the elements are arranged in order of increasing number of protons in the nucleus
20. the core electrons repelling the outer electrons, which lowers the effective charge of the nucleus on the outer electrons
21. a class of substances characterized by high electrical and thermal conductivity as well as by malleability, ductility, and high reflectivity of light

1. a column in the periodic table of the chemical elements
2. Scientific notation is a way to express numbers as the product of two numbers
4. a class of reactions in which two molecules combine, usually in the presence of a catalyst, with elimination of water or some other simple molecule
6. a high-temperature redox chemical reaction between a fuel and an oxidant usually atmospheric oxygen that produces oxidize often gaseous products in a mixture termed as smoke
8. the lowest temperature that is theoretically can be
9. a group of rare gases that include helium, neon, argon, krypton, xenon, and sometimes radon and that exhibit great stability and extremely low reaction rates
10. a chemical element that forms a simple substance having properties intermediate between those of a typical metal and a typical nonmetal
13. A chemical element (such as boron, carbon or nitrogen) that lacks metal properties and is capable of forming anions, acid oxides, acids, and stable hydrogen compounds
14. chemical reactions in which the reactants absorb heat energy from the surroundings to form products
19. any of the six nonmetallic elements that constitute Group 17