Related Clues:

• One can tell automatically oxygen involved - it's basic
• A cat is of very little matter
• A bit of a bit of a 12?
• A small thing, but half the dictionary is missing?
• It's a very little matter, like half of our letters
• Key test about to reveal smallest particle
• It's been split, the first half of dictionary?
• Small unit of matter
• Nucleus surrounded
• Smallest particle in an element able to take part in a chemical reaction
• Very small object or amount
• Tiny piece of something
• Maker of bonds
• Basic unit of a chemical element
• Its diameter is measured in picometers