Elements in the periodic table are arranged primarily in order of increasing atomic number, which is the number of protons in an atom's nucleus
. The table is structured into:
- Periods : These are the horizontal rows, numbered from 1 to 7. Each period corresponds to the filling of a different electron shell or energy level. For example, elements in the third period have electrons in three atomic orbitals or shells
- Groups : These are the vertical columns, numbered 1 to 18 (or sometimes labeled 1A to 8A and 1B to 8B in older systems). Elements in the same group have the same number of electrons in their outer shell (valence electrons), which gives them similar chemical properties
Additional details:
- The periodic table is divided into blocks (s, p, d, f) based on the electron orbital being filled
- Elements are broadly classified as metals, nonmetals, and metalloids, with metals typically on the left and center, nonmetals on the right, and metalloids along a dividing line
- The arrangement reflects periodicity: properties of elements repeat at regular intervals as atomic number increases
In summary, the periodic table arranges elements in rows by increasing atomic number and columns by similar valence electron configuration, which explains the recurring chemical properties across groups and periods.
