No, the atomic number is not always consecutive from left to right in the periodic table. The periodic table arranges elements in order of increasing atomic number, but there are instances where elements are not listed in strict numerical order.
The periodic table is organized based on the periodicity of chemical properties, which is related to the arrangement of electrons in the atoms. The elements are grouped into periods (rows) and groups (columns) based on their electron configurations and chemical behavior.
While the general trend is for atomic numbers to increase from left to right across a period, there are exceptions due to the periodic table's structure. This is primarily because the periodic table is designed to group elements with similar properties together.
For example, in the transition metals, the 3d series (from scandium to zinc) is placed between the 4s and 4p series, resulting in a deviation from strict numerical order. Similarly, in the lanthanide and actinide series, the placement of the elements is based on their electron configurations rather than strict numerical order.
Additionally, certain elements may be placed outside of the main body of the periodic table to maintain its compactness and to preserve the periodic trends. For example, the lanthanide and actinide series are often shown separately below the main table.
So, while the general trend is for atomic numbers to increase from left to right, there are exceptions and variations in the periodic table due to the organization of elements based on their chemical properties and electron configurations.