How are elements arranged in the periodic table?

Elements in the periodic table are arranged in a very systematic way to show patterns in their atomic structure and properties.

Arrangement of elements:

1. By increasing atomic number
   • The atomic number (number of protons) increases from left to right across each row.
   • This arrangement reflects the increasing number of electrons in the atom.
2. In rows called periods
   • There are 7 periods.
   • All elements in the same period have the same number of electron shells.
   • As you move across a period, properties change gradually (from metals → metalloids → nonmetals → noble gases).
3. In columns called groups
   • There are 18 groups.
   • Elements in the same group have the same number of valence electrons, so they show similar chemical properties.
   • Example: Group 1 (alkali metals) all have 1 valence electron and are highly reactive.
4. Blocks based on electron configuration
   • Elements are divided into s-block, p-block, d-block, and f-block depending on which orbital their outermost electrons occupy.
5. Metals, nonmetals, and metalloids
   • Metals are mostly on the left and center.
   • Nonmetals are on the right.
   • Metalloids (with properties of both) form a diagonal boundary between them.

In short, elements are arranged by increasing atomic number, in periods (rows) and groups (columns), so that elements with similar properties fall into the same group.