The structures in this category include the simplest, yet most relevant building blocks
that make up our world. Elements serve as the building blocks for all matter from table salt to extremely complex proteins. They are the fundamental ingredients of which all matter
is composed. Each element is represented by a unique symbol and the notations for each one can be found
in the periodic table. The periodic table contains 82-naturally occurring elements and about 31-artificially
made ones. All elements can be categorized as metals, non-metals or metalloids. Atoms of a particular element contain the same number of protons (positively charged and located in the nucleus together with the neutrons) and electrons (negatively charged, circling the nucleus) thus making it a neutral species.
Substances like common table salt are made up of electrically charged atoms (Na+Cl-). Such charged atoms, called ions, are formed by the addition or removal of electrons. Positively charged ions are called cations and negatively charged ions are called anions. Some ions may contain more than one atom and are named polyatomic ions e.g., carbonate, CO32-.