Chemical element facts: 118 elements and Mendeleev’s table

A chemical element is defined by its number of protons, so one number can identify the whole element. That number is called its atomic number, and it is the key behind the ordering that made the periodic table work.

By November 2016, the International Union of Pure and Applied Chemistry recognized a total of 118 elements. Of those, the first 94 occur naturally on Earth, while the remaining 24 are synthetic elements produced in nuclear reactions. By 2010, the first 118 elements were known, completing the first seven rows of the periodic table.

Why the atomic number matters

The periodic law says that when the elements are arranged by atomic number, an approximate recurrence of their properties is evident. That is why hydrogen, helium, and lithium sit at the start of the table with atomic numbers 1, 2, and 3.

The periodic table is an ordered arrangement of the chemical elements into rows called periods and columns called groups. It has 18 numbered groups, running from 1 on the left to 18 on the right.

Who made the first accepted periodic table?

Dmitri Mendeleev published the first recognizable periodic table in 1869. It was also the first periodic table to become generally accepted.

That table gave chemists a way to place elements in order and see repeating patterns. The later accepted structure kept the same basic idea: order by atomic number, then read the repeating properties across the rows and columns.

Which elements are natural and which are synthetic?

The first 94 chemical elements occur naturally on Earth, and the remaining 24 are synthetic elements produced in nuclear reactions. Some elements were synthesized in laboratories before it was determined that they exist in nature: technetium, promethium, astatine, neptunium, and plutonium.

This split between natural and synthetic elements is one of the clearest ways to understand the modern table. The natural ones reach 94, and the synthetic ones extend the full count to 118.

How do electron shells fit into the picture?

The first shell contains only one orbital, the 1s orbital, and can hold up to two electrons. The second shell can hold up to eight electrons, while the third shell can hold up to eighteen.

Those shell limits help explain why the table is arranged in rows and groups. The structure of the table reflects the repeating behavior of the elements as their atomic numbers increase.

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