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What is the Periodic Table?

February 4, 2013

Hi, I’m Emerald Robinson, and in this “What Is” video, we’re going to examine chemistry’s most famous illustration: the periodic table.

The periodic table is a figure that shows all of the known elements arranged in a specific order based on their chemical properties.

Chemist Dmitri Mendeelev is considered to be the “father of the periodic table,” publishing an early version of it in 1869.

The modern periodic table has 118 elements. Elements are substances made up of a single kind of atom. Neither anything smaller than an atom nor made of more than one element appears on it.

To understand how elements are arranged on the table, we need to review atomic structure. Atoms have a nucleus made up of particles called protons and neutrons. Particles called electrons orbit around the nucleus in paths increasingly distant from the nucleus, like layers in an onion. Chemists call these paths “shells.”

Elements on the periodic table are arranged in increasing atomic number; atomic number is calculated using the number of protons in each atom’s nucleus.

Rows, or “periods,” are based on the number of shells. The first row of elements, hydrogen and helium, have all of their electrons in one shell. Elements in the second row have two shells, and so on.

Elements in the same column have the same number of electrons in their outermost shells. Hydrogen and lithium each have one electron in their outermost shell. Elements in the same column have the same chemical properties.

For example, the last column, which contains elements such as helium, neon, and argon, are called the “Noble Gases.” These gases are inert, which means they don’t react easily with other elements.

As more elements are discovered in nature or synthesized in laboratories, they’re placed in the periodic table. Who knows what the table will look like in the future?



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