What is the Periodic Table?
As aforementioned, the periodic table displays the elements. The large characters of each square are the chemical symbol of that element, used in calculations, and underneath it is the element name. The number above the symbol is the atomic or proton number, and the table is arranged in increasing proton number - the proton number is unique to each element. The number below is the relative atomic mass - the average mass of all the atoms of that element, taking into account its different isotopes.
The column an element belongs to is its group. Elements in the same group have similar chemical properties, i.e. react in similar ways. The row an element belongs to is its period - this shows how many electron shells an atom of that element has. The further down the table, the larger and heavier the atom.
The table is an incredibly important tool. When chemists do calculations they need to know the numerical data corresponding to each element, but since there are so many, they use the PT for reference.
Have we discovered all the elements?
As of now (2017) there are 118 confirmed elements with no gaps in the table, the last being element 118 Oganesson (symbol: Og), recently named in November 2016 after physicist Yuri Oganessian, despite being first synthesised in 2002. It was previously called Ununoctium (Uuo) so luckily the name has become less awkward to pronounce.
I use the word synthesised, not discovered, because such heavy elements, typically with an atomic number larger than 90, do not occur naturally in nature. They are very large and thus are extremely unstable, and are usually radioactive. Scientists are constantly trying to make more of these ‘superheavy atoms‘ by various means such as fusion, because... well, I don‘t know. Maybe creating potential nuclear energy sources, unlocking the secrets of the universe, money, fame or just for the sake of scientific pursuit. The point is, we know we have discovered all the naturally occurring elements as there are no gaps in the PT, so any new superheavy elements must be artificially synthesised.
The question still remains - can we continue to make larger elements? Certainly anything is possible, but it seems highly unlikely. As atoms get larger, the outer electrons get further away from the nucleus, and are more shielded from it by the inner shells, so experience weaker forces of attraction. You can imagine that for very large atoms, the electrons in the outer shells just fly away and the whole thing falls apart as it is so unstable. When Oganesson was first synthesised only three atoms were created. There seems to be little hope for heavier elements, but somewhere out there people are still trying.
