1. – a unit of matter; the smallest unit of a chemical element

2. – a positively charged particle within the atomic nucleus

3. – a particle without an electrical charge within the atomic nucleus

4. – a negatively charged particle; can be either free (not attached to any atom) or bound to the nucleus of an atom

5. – a particle smaller than an atom, such as a proton, neutron, or electron

6. - A possible level of energy that an electron can have in an atom.

7. - The outermost electrons in an atom.

8. - A group of elements sharing similar properties.

9. - A row (left to right) of the periodic table.

10. A tabular arrangement of the elements according to their atomic numbers so that elements with similar properties are in the same column.