Atoms

1. any one of several types of very small particles that make up matter
6. the "smallest piece of matter" that if broken into smaller pieces, loses its original properties
7. arrangement of chemical elements according to atomic number
9. the energy level of a physical system (as an atom) having the least energy of all its possible states
11. The number of protons and neutrons in an atom.
13. the electrons in the outermost shell, or energy level, of an atom.
15. Center of the atom. Contains protons and neutrons.
18. one of the stable states of constant energy that may be assumed by a physical system -- used especially of the states of electrons in atoms
19. any number of entities (members) considered as a unit
20. An atom with a charge. Number of protons does not equal number of electrons.

2. Average mass number of all isotopes of an element
3. Particle in atom with no charge (neutral).Located inside the nucleus.
4. Atoms of the same element with different numbers of neutrons
5. Particle in atom with a positive charge. Located inside the nucleus
8. a theory of the structure of the atom
10. any of the forms of an element that differ in the number of neutrons in an atom
12. the smallest particle of a substance having all the characteristics of the substance and is composed of one or more atoms
14. The number of protons in an atom.
16. a substance that cannot be broken into smaller pieces
17. Particle in atom with a negative charge. Located outside the nucleus.