The main distinguishing factor between the various chemical elements is the number of protons in an element's nucleus, which is known as the element's atomic number. The atomic number also corresponds to the number of electrons the element has because elements have equal numbers of protons and electrons.
As of 2014, 118 elements have been discovered. The most recent element to be discovered was ununseptium, which was first reported to have been synthesized in 2010. This element has an atomic number of 117, which is the second highest atomic number on the periodic table. It is second in number only to ununoctium.
The atomic structure of the element changes depending on its atomic weight and number, which is why some elements are more stable than others. This is also why some elements are found in liquid at room temperature, while others naturally occur as either a solid or a gas.
The periodic table of elements is divided into groups of elements that all have similar characteristics. There are 10 trivial groupings of elements on the periodic table, including noble gases, alkali metals, alkali earth metals, semi-metals and non-metals. The other five groups are transition metals, basic metals, lanthanides, actinides and halogens.