A. The building bricks of the world

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Across
  1. 2. The central part of an atom
  2. 5. It is one of the physical properties of matter, together with density
  3. 8. The temperature at which a solid becomes a liquid
  4. 11. A part of an atom that has no electrical charge
  5. 12. The temperature at which a liquid becomes a gas
  6. 14. A small piece of matter with a negative electrical charge
  7. 15. The physical substance the universe is made of
  8. 16. A small piece of matter with positive electrical charge
Down
  1. 1. It includes the study of chemical elements, compounds and chemical reactions
  2. 3. It is made up of two or more chemically bonded elements
  3. 4. A state of matter that is neither liquid nor gas
  4. 6. The temperature at which a liquid becomes a solid
  5. 7. The smallest unit of a chemical element
  6. 9. A state of matter that is neither liquid nor solid
  7. 10. A state of matter that is neither solid nor gas
  8. 13. It is a synonym for "state"
  9. 14. A chemical substance that is made of atoms all of the same kind