Atom and Periodic table vocabulary: 1. The mass on the periodic table.
2. Particles that differ in number between isotopes.
3. Vertical column in the periodic table.
4. Atoms of the same element that have different masses.
5. All elements in the same one of these has the same number of energy levels in their electron cloud.
6. The smallest form of matter that still retains the properties of an element.

key:
Neutrons
Quark
Average atomic mass
Isotopes
Group
Period