Why are the elements placed in specific places on the periodic table? 2. periods are rows that run from left to right . 3. elements in the same period have the same number of orbitals. 4. every element in the first period has 1 shell for its electrons. every element in the second period has 2 for its electrons. see the pattern? 5. groups are columns that run from top to bottom. 6. the elements of a group have the same number of valence electrons in their outer shell. 7. every element in group one has 1 electron in its outer shell. every element in group two has 2 electrons in its outer shell. 8. hydrogen is special because it can act like two groups, 1 and 7 . 9. hydrogen sometimes is missing an electron and sometimes it has an extra electron. 10.although helium has only electrons in its outer shell, it is grouped with elements that have