Summary Of Periodic Table Trends

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Summary of Periodic Table Trends

Atomic Radius //Period// - atomic radius __decreases__ as you go from left to right across a period.

Why?

Stronger attractive forces in atoms (as you go from left to right) between the opposite charges in the nucleus and electron cloud cause the atom to be 'sucked' together a little tighter.

//Group// - atomic radius __increases__ as you go down a group.

Why?

There is a significant jump in the size of the nucleus (protons + neutrons) each time you move from period to period down a group. Additionally, new energy levels of elections clouds are added to the atom as you move from period to period down a group, making the each atom significantly more massive, both is mass and volume.

Ionization Energy (Ionization energy is the amount of energy required to remove the outmost electron. It is closely related to electronegativity) //Period// - ionization energy __increases__ as you go from left to right across a period.

Why?

Elements on the right of the chart want to take others atom's electron (not given them up) because they are close to achieving the octet. The means it will require more energy to remove the outer most electron. Elements on the left of the chart would prefer to give up their electrons so it is easy to remove them, requiring less energy (low ionization energy).

//Group// - ionization energy __decreases__ as you go down a group.

Why?

The shielding affect makes it easier to remove the outer most electrons from those atoms that have many electrons (those near the bottom of the chart).


Electronegativity

(Electronegativity is an atom's 'desire' to grab another atom's electrons)

//Period//- electronegativity __increases__ as you go from left to right across a period.

Why?

Elements on the left of the period table have 1 -2 valence electrons and would rather give those few valence electrons away (to achieve the octet in a lower energy level) than grab another atom's electrons. As a result, they have low electronegativity. Elements on the right side of the period table only need a few electrons to complete the octet, so they have strong desire to grab another atom's electrons.

//Group// - electronegativity __decreases__ as you go down a group.

Why?

Elements near the top of the period table have few electrons to begin with; every electron is a big deal. They have a stronger desire to acquire more electrons. Elements near the bottom of the chart have so many electrons that losing or acquiring an electron is not as big a deal. This is due to the shielding affect where electrons in lower energy levels shield the positive charge of the nucleus from outer electrons resulting in those outer electrons not being as tightly bound to the atom.

Here is an interesting webpage (in Java) with the periodic trends: http://chemmac1.usc.edu/java/ptable/ptable.html