What is the Periodic Table of Elements?

2019 marks the 150 year anniversary of the Periodic Table. With over 100 elements, it can seem very complex and intricate. Each element has a symbol and is grouped into rows and columns.


Elements are simple substances that make up all matter. For example, water is made by combining the elements hydrogen and oxygen. Elements are listed in the table by the structure of their atoms. An atom is the smallest particle of an element. From left to right and top to bottom, the elements are listed in the order of their atomic number, which is the number of protons in each atom. A proton is a positively charged particle in the nucleus. The nucleus is the central part of an atom.


The periodic table was proposed by Russian chemist Dmitri Mendeleev in 1869. It is called “periodic” because elements are lined up in cycles or periods. From left to right elements are lined up in rows based on their atomic number. Using the table, Mendeleev was able to accurately predict the properties of many elements before they were actually discovered!


Each element has its own name and abbreviation in the periodic table. Some of the abbreviations are easy to remember, like H for hydrogen. Some are a bit harder like Fe for iron or Au for gold. For gold the “Au” comes from the Latin word for gold “aurum”.


Columns (groups) are vertical sets of elements with a similar number of valence electrons. An electron is a negatively charged particle that is lost or gained by an atom in a reaction. Valence electrons are the most reactive electrons in an atom. Therefore, elements in the same group tend to have similar chemical properties, such as forming bubbles when reacting with water.


Horizontal rows in the Periodic table are called periods. There are a number of trends that occur across a period. The first two members of period 3 are sodium (Na) and magnesium (Mg). In reactions, they both tend to lose electrons, but sodium loses one electron, while magnesium loses two. Chlorine (Cl), down near the end of the period, tends to gain an electron. Therefore, one trend is that elements tend to gain electrons as you move from left to right.


In 2016, four new elements were added to the periodic table: nihonium, moscovium, tennessine, and oganesson. It is possible that in the future, even more elements will be discovered.

Marwin Ramos


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