chemistry

3. negatively charged particle in an atom
4. code of one or two letters that represent an element
6. an electron in the outer shell of an atom
8. set of chemical symbols that represent a compound
10. a chemical bond in which electrons are shared
12. the number of protons in an atom
13. change in form of matter that does not result in a new substance being produced
15. positively charged particle in an atom
16. a chemical bond in which electrons are transferred from one atom to another
17. small, dense region of an atom made up of protons and neutrons
18. a pure substance of one type of atom

1. matter that is composed of two or more separate elements
2. the basic building block of matter
5. a change in which chemical bonds are broken or formed resulting in a new substance being produced
7. process in which one or more substances are changed into one or more different substances
9. the number of protons plus neutrons in an atom
11. the subatomic particle with no net charge
14. the smallest unit of a chemical compound that can take part in a chemical reaction