Periods and Classification of Elements

Periods in the Periodic Table  

The periods are the seven horizontal rows in the periodic table. Each period represents a set of elements that have the same number of electron shells.  

- As we move across a period, the number of valence electrons increases by one for each successive element.  

- However, the chemical properties and reactivity of elements in the same period do not necessarily remain the same, since the type of element changes from metallic to non‑metallic across the row.  

For example, sodium (Na) and chlorine (Cl) belong to the same period but have very different chemical behaviours. Sodium is a reactive metal, while chlorine is a reactive non‑metal.  

Classification of Elements  

Based on their physical and chemical properties, elements are broadly classified into three categories:  

- Metals: Good conductors of heat and electricity, malleable, ductile, and usually solid at room temperature.  

- Metalloids: Show properties of both metals and non‑metals. Common metalloids include boron, silicon, germanium, arsenic, antimony, polonium, and tellurium.  

- Non‑Metals: Poor conductors of heat and electricity, brittle in solid form, and often gaseous.  

Insight:  

The arrangement of elements into periods and classifications helps scientists predict their behaviour, bonding patterns, and reactivity, forming the foundation of modern chemistry.