The occupancy of the electron shells (energy levels) on a atom of an element can be correlated with the number of the group in the periodic table in which the element is found.
Elements in the
The first four periods (rows) of the periodic table are shown.
These contain many important elements.
The number of electrons in this outer shell is equal to the last digit of the group number.
Elements in the
same period (row) have their outer electrons in the same shell.
same group (column) have the same number of electrons in their outer shell.
same group (column) have the same number of electrons in their outer shell.
| 1 | 2 | ||||||||||||||||
| 1H |  | 2He | |||||||||||||||
| 3Li | 4Be | 5B | 6C | 7N | 8O | 9F | 10Ne | ||||||||||
| 11Na | 12Mg | 13Al | 14Si | 15P | 16S | 17Cl | 18Ar | ||||||||||
| 19K | 20Ca | 21Sc | 22Ti | 23V | 24Cr | 25Mn | 26Fe | 27Co | 28Ni | 29Cu | 30Zn | 31Ga | 32Ge | 33As | 34Se | 35Br | 36Kr |
The first four periods (rows) of the periodic table are shown.
These contain many important elements.
The number of electrons in this outer shell is equal to the last digit of the group number.
Sodium (Na) and lithium (Li) are in Group 1.
| Lithium has 3 electrons. Two are in shell 1. One is in shell 2. represented by 2,1 OR  |
| Sodium has 11 electrons. Two are in shell 1 Eight are in shell 2. One is in shell 3. represented by 2,8,1 OR  |