The Modern Periodic Table of Elements is arranged by

The Modern Periodic Table of Elements is arranged by atomic number. The atomic number refers to the number of protons found in the nucleus of an atom. The elements are also grouped into different categories based on their properties, including alkali metals, alkaline earth metals, transition metals, halogens, and noble gases.

Here are the steps:

1. The first step in arranging the modern periodic table is to list the elements in order of increasing atomic number.

2. The second step is to group the elements into periods (rows) and groups (columns). The elements in each period have the same number of atomic orbitals. For example, all elements in the top row (the first period) have one orbital for their electrons. All elements in the second period have two orbitals for their electrons.

3. The third step is to group elements into columns based on their properties. Elements in the same group (also known as a family) have similar chemical and physical properties. For example, all noble gases are in the same group and they are all unreactive.

4. The final step is to place the lanthanides and actinides, two series of elements that were discovered after the original periodic table was devised, at the bottom of the table. These elements were placed here because they fit better in terms of their properties and it keeps the table more compact.

So, the modern periodic table is arranged by atomic number, but also takes into account the arrangement of electrons and similarities in properties.