Periodic Trends

One of the best qualities of the periodic table is its ability to help predict properties of elements by their position on the table. There are four traits we will look at:

Atomic Radius - The distance from the nucleus to the outermost electron. The size of the atom.
Ionization Energy - How much energy is needed to remove an electron from the atom.
Electron Affinity - How much energy is released when an electron is added. The opposite of Ionization energy.
Electronegativity - How strongly the atom attracts electrons shared in a bond.

Atomic Radius

Electrons are held to the atom by the attraction to the nucleus. More protons in the nucleus increases this attraction. Therefore increasing atomic number across a period decreases the atomic radius. However, radius suddenly spikes when moving to the next period. For example Argon (Ar) is small, but the next element Potassium (K) is much larger. This is because at this point a new electron energy shell has been introduced. The atomic radius always increases when a new shell has been added.

Effectively the bottom left corner has the largest elements, Francium (Fr) being the largest. The top right corner is the smallest, Helium (He) being the smallest.

Ionization Energy

Ionization energy follows the opposite trend from atomic radius. The smaller the atom the more tightly it holds onto it's electrons. It takes the most energy to remove electrons from the noble gases. This is to be expected because they have complete energy shells and do not want to lose any electrons.

Electron Affinity

If it takes energy to remove electrons then the opposite action, adding electrons, will release energy. The atoms with incomplete energy shells will release the most energy. Therefore Fluorine is has the highest electron affinity. Noble gases do not have a high electron affinity because they already have a complete electron shell.

Electronegativity

When electrons are shared in a bond the nuclei of the atoms sharing them compete for the electrons. Smaller atoms will have a larger pull on the electrons, however, noble gases do not form bonds and so their electronegativity cannot be calculated.

Fluorine is the most electronegative atom and Francium is the least.

Reactivity

Atoms react when they transfer electrons. So elements that have a strong pull on electrons, like fluorine are extremely reactive. Fluorine is missing one electron from its valence shell, and is desperately trying to gain one more. Elements near Fluorine in the top right corner of the periodic table are also highly reactive. However, elements at the opposite end of the periodic table in the bottom left corner, like Francium (Fr), are also extremely reactive. This is because they have too many electrons in their outer shell and want to get rid of an electron.

06 Periodic Table.pptx

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