The Periodic Quest: Quite element-ary

            Before I begin, I need to explain the fact that myself and both of my older brothers are all studying some form of Chemistry. So, for Christmas this year our family board game was "Periodic Quest," which is a board game that involves moving along a Periodic Table, using die, and cards (one for each element) to play different variations of the game - some based on properties of the elements and others simply on atomic number.  

            We finally all sat down to play the game a few nights ago and it was...enlightening to say the least. My brother Stephen and I had forgotten that not everyone has an extensive working knowledge of the Periodic Table. My parents had both taken Chemistry courses before, in High School and College, but after years of doing nothing with Chemistry they were very very rusty.

            So, to help my parents out, I am doing this post about the Periodic Table - its history, uses, and organization.

The history

            We need to go back all the way to 1869 and a Russian chemistry professor named DmitrI Mendeleev. When he was teaching, there were around 60 known elements (compared to the 118 of today) and he began his table by ordering the elements by atomic weight - the heaviness of an atom of an element compared to an atom of hydrogen. Mendeleev was writing his own Chemistry text, and as he ordered the elements horizontally he found that if he left gaps he found periodic (see what he did there) vertical trends in the properties of some elements.

From http://www.aip.org/history/curie/periodic.htm

            He left these gaps and claimed that there were yet undiscovered elements that would fill in the table and adhere to both the horizontal and vertical trends identified. With this as a guide, some early Chemists (later 1800s) were able to discover elements that fit within the gaps that Mendeleev had claimed would be filled. After these elements were discovered, his table began to grow in importance.

The Uses

            The first huge use of the Periodic Table is the atomic weight. This means the weight of the nucleus of an atom of the element. This is generally around double of the element's atomic number - i.e. Hydrogen is number 1, etc. The atomic number is the number of protons in the nucleus of an atom of an element. The atomic weight is generally double that of the atomic number because protons (positively charged particles) and neutrons (neutrally charged particles) both exist within the nucleus and are approximately the same weight. The electrons (the negatively charged particles) exist outside of the nucleus in orbitals and have a minimal weight.

            The horizontal trends of the Periodic Table or the "periods" reveal the trends of atomic radius, ionization energy, electron affinity, and electronegativity. As you move across a period, the atomic radius decreases, as the additional protons and neutrons cause the electrons to be draw closer to the nucleus. The other trends all act opposite to the atomic radius and increase as you move across the period. Ionization energy is the amount of energy required to remove an electron. The electron affinity is the amount of energy released when an electron is added to an atom to make a negative ion (from neutral to negative). The electronegativity is how much an atom wants electrons.

Periodic trends descriptions - here!

            The vertical trends or "groups" (or "families") show some more significant properties. It must be realized that elements in the same groups have the same number of valence electrons or electrons in the outermost orbital and this corresponds to the trends the exhibit. The most recognized families are the Alkali metals (1), the Alkaline Earth metals (2), Halogens (17), and the Nobel gases (18).  Groups 3 to 10 show less strong relationships and thus don't get cool names.  Some of the trends revealed by the Periodic groups are: the atomic radius increases as you move down a family, a decrease in ionization energy (since they are bigger and are held together less tightly), and a decrease in electronegatitvity. A fun trend found in  Family 1 or the Alkali metals is that they are exceedingly reactive with water (see below).

            The two rows set of by themselves at the bottom of the Table are arranged as such because they do not quite fit the trends of the rest of the table. This is because they are radioactive, and it makes the table more aesthetically pleasing.

            I think that is enough of an overview for today. Needless to say, we didn't really end up playing the game. Instead, my brother and I got to spend the time explaining the Periodic Table and its many uses to our parents. And you know what - we had a blast.

Interactive Periodic Table - here!

Fun comic explanation - here!