Up and Atoms

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Across
  1. 2. A pure substance made up of chemically combined atoms in a fixed ratio
  2. 4. Has mass and takes up space
  3. 7. Columns on the Periodic Table
  4. 10. The average mass of atoms of an element, calculated using the relative abundance of isotopes in a naturally-occurring element.
  5. 12. Unstable isotopes that decay by releasing radiation
  6. 15. Neutral particle in the nucleus of the atom
  7. 16. A table containing all the known elements in order of atomic number
  8. 19. An impure substance made up of pure substances physically mixed.
  9. 20. Elements on the right side of the Periodic Table
  10. 21. Radiactive decay made up of gamma rays
  11. 22. Levels where electrons are found
  12. 23. Negative particle of the atom that orbits the nucleus
  13. 24. Atoms with the same atomic number and different mass number
  14. 25. The time taken for the radioactivity of a specified isotope to fall to half its original value.
Down
  1. 1. The dense centre of an atom containing protons and neutrons
  2. 3. Also called semi-metals, have some properties of both metals and non-metals
  3. 5. Building blocks of matter
  4. 6. The mass of an atom calculated by adding the number of neutrons to the number of protons for an atom
  5. 8. Positive particle in the nucleus of an atom
  6. 9. Elements on the left side of the Periodic Table
  7. 10. Radioactive decay made up of a helium nucleus
  8. 11. Radiation released due to the decay of the nucleus of an atom
  9. 13. The number of protons in an atom of a particular element
  10. 14. Rows on the Periodic Table
  11. 17. Radioactive decay made up of an electron
  12. 18. An atom that has lost or gained electrons