Chemistry

3. Basic building block of chemistry.
8. The outside part of an atom around the atomic nucleus.
9. Represents the number of protons and electrons in an atom.
11. A substance that can't be broken down into simpler components by any non-nuclear chemical reaction.
12. One or two letters that are to identify an element.
15. A particle which is smaller than an atom.
17. What holds atoms together in molecules.
19. A small particle that has a negative charge of electricity and travels around the nucleus of an atom.
20. A subatomic particle found in the nucleus of every atom.

1. Form when two or more elements chemically combine.
2. A combination of symbols that shows the ratio of elements in a compound.
4. The system of electrons surrounding the nucleus of an atom.
5. The positively charged center of an atom and contains most of its mass.
6. A neutral subatomic particle that is a constituent of every atomic nucleus except ordinary hydrogen.
7. The sum weight of the protons and neutrons in an atom.
10. When a positively charged ion forms a bond with a negatively charged ion one atom donates electrons to the other.
13. Made up of one or more atoms.
14. A chemical bond formed when two atoms share pairs of electrons.
16. Electrons that are located in the outermost electron shell of an element.
18. A number in the chemical formula that tells the number of atoms in a molecule.