1) neutrons
2) by the number of protons
3) electrons
4) bohr's model
5) mass number
6) the basic unit of a chemical element
7) isotopes
8) j.j. thompson
9) bohr said that electrons are located in orbital while the cloud model meant that the electrons are shattered
10) by atomic masses
11) period is horizontal while group is vertical
12) whether it's a metal, nonmetal, metalloid, etc
13) number of valence electrons
14) by atomic number
15) group
hopefully this helps! :) have an amazing day!
