Elemental Tales: Comic 8

There are several different methods that have been created to calculate the electronegativity levels of atoms (the Pauling Scale, the Mulliken Scale, the Allred-Rochow Scale, the Sanderson Scale, the Allen Scale, etc.).  Although these different methods may have small differences in the numerical values of the electronegativity, they all still show the same periodic trends between elements.  In general, electronegativity level increases as you go higher up the periodic table (from bottom to top), and also as you go from left to right of the periodic table.

The most commonly used method to calculate the electronegativity levels of atoms is the Pauling Scale.  Look at this link below....the Pauling Scale is the first chart in this link:

The opposite of electronegativity is electropositivity.  Electropositivity is a measure of an element's ability to donate electrons to other elements.  The lower an element's electronegativity is, the higher their electropositivity is.  In general, electropositivity level increases as you go from right to left of the periodic table, and also as you go down the table (from top to bottom).  So that means that fluorine has the lowest electropositivity level at 3.98, and cesium has one of the highest electropositivity levels at 0.79.  (Only francium has a higher electropositivity than cesium.)  So that's why, in the comic, Cesium shows her charitable side by wanting to donate electron cookies, while Fluorine shows her non-charitable side by not wanting to donate any electron cookies.

The electrons in the outermost shell of an atom are called valence electrons.  Most atoms need 8 valence electrons to have a full shell and be stable.  Halogens (such as fluorine) have 7 valence electrons, so they only need 1 more electron in their outermost shell to have a full shell.  If they get that extra electron (like Fluorine does in the last panel of the comic), then they become a negatively charged ion (indicated by a minus sign next to their element symbol).  A fluorine atom (F) with an extra electron is called fluoride (F^-).

Meanwhile, alkali metals (such as cesium) only have 1 valence electron.  So an alkali atom is not interested in gaining electrons.  It would rather donate that lone electron it has in its outermost shell, so that the next electron shell below it (which is a full shell) becomes the new outermost shell, making the alkali metal stable.  Alkali metals, with their 1 valence electron, and very low electronegativity numbers, are very "charitable," wanting to donate electrons to achieve stability.  Halogens, with their 7 valence electrons, and high electronegativity numbers, are very "greedy," because they are so close to achieving stability (only needing 1 more electron).