Summary

• The periodic table of the elements lists all the known elements, in a way that reflects periodic trends in their physical and chemical properties.

• Elements are listed in order of increasing atomic number (proton number) and arranged into groups (columns) and periods (rows).

• The layout of the periodic table arranges groups so that they contain elements with similar physical and chemical properties.

• These include alkali metals, alkaline earth metals, halogens and noble gases.

• The layout also reflects patterns in the electron configuration of elements.

• Main groups contain elements with the same number of valence electrons, therefore, they form ions with the same charge.

• Periods contain elements with the same number of electron shells.

• Atom size increases down groups and decreases across periods.

• For metals, reactivity increases down groups and decreases towards the centre of the periodic table (excluding transition metals).

• For non-metals, reactivity decreases down groups and decreases towards the centre of the periodic table (excluding noble gases).

(Image: Jynto, Wikimedia Commons)