Periodic table is a table of elements in terms of rows and columns in terms of their chemical and physical properties.
Elements in the same group or columns have similar physical and chemical properties. For example, elements in the same group have the same number of valence electrons or valency.
Elements in the same period or rows have similar number of energy levels. For example, potassium and bromine belong to the same period in the periodic table and thus have the same number of energy levels.
