Layout of the Periodic Table
Rows = periods. Columns = groups. Order = atomic number.
The Periodic Table contains all known elements, arranged in order of increasing atomic number (Z). The shape is no accident β elements line up by their chemical properties.
Periods are the rows (1 to 7). The period number tells you how many electron shells the element's atoms have. Period 2 elements have 2 shells (e.g. Li, Be, B, C, N, O, F, Ne); Period 3 have 3 shells.
Groups are the columns (1 to 18, or 1, 2, 3-12, 13-18 with old notation). Elements in the same group have similar chemical properties because they have the same number of outer-shell electrons. For main-group elements:
- Group 1 = 1 outer electron (alkali metals: Li, Na, K ...).
- Group 2 = 2 outer electrons (alkaline earth metals).
- Group 7/17 = 7 outer electrons (halogens: F, Cl, Br ...).
- Group 0/18 = 8 (or 2 for He) β full outer shell, NOBLE GASES.
- Arranged by atomic number (Z).
- Periods = rows; period number = number of shells.
- Groups = columns; same group = same number of outer electrons = similar chemistry.
- Metals on left, non-metals on right.