Periodic Trends:

Based on how the elements are situate on the periodic table, there are 3 trends that can be observed:

  1. Electronegativity
  2. Atomic Radius
  3. Ionization Energy

To fully understand and relate the 3 trends together, there is only 1 piece of information to know, and that is electronegativity and that Fluorine is the most electronegative out of all elements.

What is electronegativity?

It is designated by the greek letter delta δ and it is defined as the ability for an atom to attract electrons to a bond.  If an element is more electronegativity, then it has a greater ability to attract electrons to itself to form a bond.  If there are two atoms that are bonded together, and one atom is more electronegative than the other, then there is more electrons (density) near the electronegative atom.  

A good way of thinking about electronegativity is thinking about a person giving itself a “self hug”.  The stronger the “self hug”, the better it pulls electrons to itself. And if there are two people together, then the one that can “hug” harder or pull the electrons to itself stronger will have more of the electrons.

Screen Shot 2015-09-29 at 8.33.45 PM






So now that the definition is out of the way, one bit of information to remember is the Fluorine is the most electronegative element that exists.

If Fluorine is the most electronegative, then the trend of electronegativity is this,

It increases across the periodic table (towards Fluorine)

and it increases up (towards fluorine).

Screen Shot 2015-09-29 at 8.37.10 PM

If you can make sense of electronegativity, then the atomic radii will follow.

Atomic radius is essentially the size of the atom. The larger the atomic radius, the larger the atom.

Now, relate this knowledge with electronegativity. If electronegativity is the ability of an atom to pull electrons to itself, then the higher the electronegativity value, the smaller the atomic radius and vice versa.

Therefore, the atomic radius decreases across (towards the strong fluorine) and decreases up (towards the fluorine)

Screen Shot 2015-09-29 at 8.39.10 PM

What about atomic radius of ions such as cations (+) and anions (-)?

First, cations are ions that have lost an electron while anions are ions that have gained electrons.

So if cations have lost electrons, then there are more protons than electrons, this means that there is a stronger attraction between the + and – charges. Thus, the atomic radius should be smaller than a neutral atom.

However, in an anion, there are more electrons than protons, because of this reason, the electrons are actually ‘shielded’ from the positive protons, making them more distant from the nucleus. Thus, the atomic radius of anions are larger than neutral atoms.

Last trend, ionization energy.

At this point, you have only memorized 1 fact of Fluorine and electronegativity and deduced atomic radius.  Now, use the same logic and see if you can deduce the trend of ionization energy.

Ionization energy is the amount of energy to take or remove an electron from the atom.  The higher the ionization energy, the harder to remove the electron.  You should be able to use logic to make sense of this trend.

Since fluorine is incredibly electronegative, it is really hard to remove electrons away since it holds them or attracts them quite well, thus, ionization energy increases across the periodic table (towards fluorine) and increases up (towards fluorine).

Screen Shot 2015-09-29 at 8.44.14 PM

By looking at the valence electrons and relating to the orbitals of the elements, the first ionization energy is the amount of energy to remove the first electron.

The first ionization energy is generally lower for elements with only 1 valence electron on its outer shell.  But as we remove more electrons (the successive ionization energy), ionization energies will increases if the electrons are found in a complete shell.


Screen Shot 2015-09-29 at 8.46.43 PM