The Periodic Table

The Periodic Table Overview

  • The Periodic Table is a methodical arrangement of elements, ordered by their atomic number, electron configuration, and recurring chemical properties.
  • The vertical groups on the table highlight elements having the same number of valence electrons, which affects their reactivity.
  • The horizontal periods reflect recurring trends in the elemental properties, a phenomenon also known as periodicity.

Groups and Periods

  • Groups (vertical columns) in the Periodic Table are numbered from 1 to 18, and they define the number of electrons in the outer shell of the atoms.
  • Periods (horizontal rows) are numbered from 1 to 7, reflecting the number of electron shells around the nucleus of the atoms.

Metals, Non-metals and Metalloids

  • Metals are typically located on the left of the Periodic Table and incline towards transferring electrons in chemical interactions, hence they are often cations.
  • The majority of non-metals, usually found on the right of the table, receive electrons to create anions.
  • Metalloids or semi-metals, which have attributes of both metals and non-metals, demarcate a diagonal step-like region between the two.


  • The Periodic Table is divided into blocks: the s-block (Group 1 and 2 elements), p-block (Groups 13 to 18), d-block (transition metals), and f-block (the lanthanides and actinides).
  • Each block corresponds to the filling of a different type of orbital: s, p, d, and f respectively.

Atomic Radii, Ionisation Energy and Electronegativity

  • Atomic radii decrease across a period from left to right and increase down a group due to increasing energy levels.
  • Ionisation energy generally increases across a period from left to right and decreases down a group due to atomic size and the effect of shielding.
  • Electronegativity, a measure of the capability of an atom to attract bonding electrons, increases from left to right across a period and decreases down a group.

Trends in the Periodic Table

  • Trends depend on atomic structure and they influence an element’s chemical reactivity and physical properties. These include variation in ionic radius, electrical conductivity, and melting and boiling points.
  • Understanding these trends in the Periodic Table helps interpret and predict simple reactions and behaviours of elements.