Chapter 9

4. An electron in the outermost energy level of an atom.
6. 1 more electron than proton.
7. Average mass of the naturally occurring isotopes of an element.
8. An atom that carries an electrical charge.
11. Tiny, very light particles that have a negative electrical charge and move around the outside of the nucleus.
12. Much larger and heavier than electrons, have a positive charge, and located in the nucleus of the atom.

1. Equal to the number of protons plus neutrons.
2. Often used for things that are too small or too large to be observed or that are too difficult to be understood easily.
3. 1 less electron than proton.
5. Any of the possible energies an electron may have in an atom.
7. Number of protons and shown on the periodic table with the element.
9. Large and heavy, have no electrical charge, and located in the nucleus of the atom.
10. Two atoms with different numbers of neutrons, the number of neutrons can change, and the number of protons for a given atom never changes.