The element with highest atomic number till discovered

 Oganesson: The element with highest atomic number

Based on the origin and method of creation, chemical  elements are classified into natural or synthetic elements. Natural elements naturally exist on the earth and in the universe, formed through natural processes such as fusion reactions in stars, supernova explosions and radioactive decays. Hydrogen, oxygen, nitrogen, iron, gold, urannium are the examples of natural elements.
    On the other hand, synthetic or artificial elements are those created artificially by humans by nuclear reaction or particle accelerator. These do not occur naturally on earth and are created in laboratory. Synthetic elements are typically created by bombarding a target nucleus with high-energy particles to induce nuclear reactions. These reactions result in the formation of new, heavier elements. Technetiu, Promethium, Americium are some examples of synthetic elements. The matter of discussion in this article, the element Oganesson is also a synthetic element.
   
Oganesson is the element with highest atomic number

Professor Yuri Oganessian, from which Og comes
By Armenia Post - https://www.haypost.am/en/1485236103, Public Domain, https://commons.wikimedia.org/w/index.php?curid=65280651
 In 2006, a joint team of scientists from Russia and America were working at Institute of Dubna (Joint Institute for Nuclear Research), Russia on particle accelerator (U-400 cyclotron). They bombarded Carlifornium-249 with ions of calcium-48 and got Oganesson-118 having a half life of just 0.89 miliseconds. This element gets a place in 7th period and 18th group of the periodic table having atomic number 118 and mass number 294. It has two other isotopes of less stabilities having mass number 293 and 295.
Oganesson is a non metal noble gas element of electronic contribution expected to be:

[Rn]86 5f14 6d10 7s2 7p6 and various oxidation states are -1, 0, +1, +2, +4 which suggest that even though it is present in group 18 it is reactive.

The name Oganesson and symbol Og was confirmed in 2016 which was taken  from eminent Professor Yuri ogannesian for his leading discoveries in the field of trans-actinoid elements. It is one of two elements named after a peson who was alive at the time of naming, the other being the  seaborgium, named after Nuclear Chemist Glein T. Seaborg.
 The structure of XeF4 is square planar, where OgF4 is expected to be tetrahedral.