periodic table of elements

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Across
  1. 5. the elements are listed in order of increasing atomic number.
  2. 6. electron the number of electrons present in the outermost energy shells
  3. 10. a horizontal row of the periodic table
  4. 11. section to the right of the metalloids
  5. 15. subatomic elementary particles located in the nucleus of every atom, except atoms of hydrogen
  6. 16. metal any of various chemical elements that have valence electrons—i.e., electrons that can participate in the formation of chemical bonds—in two shells instead of only one
  7. 18. most reactive non-metal
  8. 19. An element that is not a metal but that has some properties of metals
Down
  1. 1. mass the average mass of the atoms of an element measured in atomic mass unit
  2. 2. bond of complete transfer of valence electron(s) between atoms.
  3. 3. metal most reactive group
  4. 4. a positively charged particle that resides within the atomic nucleus
  5. 7. negatively charged particles of atom
  6. 8. bond that involves the sharing of electron pairs between atoms
  7. 9. atomic mass unit
  8. 10. most reactive metal
  9. 12. a vertical column of the periodic table
  10. 13. section to the left of the metalloids
  11. 14. number is the number of protons in the nucleus of an atom
  12. 17. a particle of matter that uniquely defines a chemical element