Atomic Structure and the Periodic Table

The Discovery of the Periodic Table

In the 1800`s, lots of chemists were trying to come up with a way to depict all the elements into table, and a lot of forms were proposed.

But Dmitri Mendeleev`s table became the one we use today, because how well it correlates data and predictive powers.

He arranged the rows into periods, and columns called groups. Elements that had similar behavior were put in groups together, also helping correlate existing data, and also predicting the existence of other elements.

Mendeleev left a few empty spots in his table and predicted the existence of other elements as well.

These gaps were then filled with the discovery of these elements with the help of the properties as expected

The Periodic Table

The table consists of metals, non-metals and metalloids.

The reason Mendeleev was able to predict the elements, was because the elements behaved similarly is because they have the same number of valence electrons.

If we take group 1 for example, the elements all have the valence electron of 1 or 1 electron in their outermost shell.

As you go down the table and n increases, you gain a shell each time, but whichever is the outermost shell, there is only one electron in it.

There are some periodic trends we can identify from the table.

The atomic radius or the size of the atom.

****As we go further down the table, the atomic size increases, because we add shells. On the right the size decreases as we are moving within a shell and each element to the right has one more proton in the nucleus than the last, so there is a stronger electromagnetic attraction in the electrons, meaning the atomic radius shrinks.

The electromagnetic force in the electron, which is attracted to the protons, so the further the nucleus is from the electron, the easier it is for them to break apart the contact.

This proves that the ionization energy trend is contradicting towards the atomic radius trend.

Francium, a very large atom, with only one valence electron, usually has a lot of outermost shells and has a weaker connection to its electrons and can be easily ionized due to, the atom being larger, therefore separating the electron from the atom.

On the other hand, more like on the other side of the periodic table, Helium, a gaseous element has only one shell, so the electrons are very close to the nucleus, therefore the bond is stronger.

So, it naturally requires much more energy to ionize helium.

Therefore, the ionic energy increases as we go up and right on the table.

Successive Ionic Energies (kg/mol)

elements can have ionization energies for removing mor than one electron.

A second ionization will always be greater than the first and will continue to increase from there.