There is a reason behind the placement of each element on the periodic table. We have quickly been learning the reason behind the specific placements. This week, we are talking about electronegativity and why certain transition metals have a higher electronegativity than the elements to the right of them. Electronegativity is known as the ability of an atom in a compound to draw electrons to itself. Therefore, unlike other properties of the periodic table, electronegativity does not have actual trends, but instead is a way of combining two other periodic trends, ionization energy and electron affinity. “Ionization energy is the amount of energy required to remove an electron from a neutral atom. Electron affinity is the amount of energy given off or required when a neutral atom gains an electron” (Murmson, 2020). While electronegativity is supposed to go from left to right on the periodic table, there are certain transition metals that have a higher electronegativity than the elements to the right of them. The elements to the right consist of noble gases. Noble gases possess a complete valence shell and typically do not attract electrons. Certain transition metals do have the capability of attracting electrons to themselves. Therefore, if noble gases are unable to attract electrons to themselves, which is the meaning of electronegativity, they would not have an electronegativity value.
Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. The periodic table increases in electronegativity from left to right. When a valence shell of an atom is less than half full, it requires less energy to lose an electron than to gain one. On the other hand, when the valence shell is greater than half full, it is easier to pull an electron into that valence shell than to donate one. Certain groups are excluded from this rule, those being the Noble Gases, Lanthanides, and Actinides. The Noble Gases in particular already have a full and complete valence shell filled with 8 electrons and therefore do not usually attract or share electrons (which makes them very stable). The Lanthanides and Actinides are a bit more complicated in their chemical composition that enables them to not follow the traditional rules as stated above. They also have properties that put them in the same block as the f block (which is too full to house them while keeping the shape of the table). Pulling them out enables the table to function otherwise successfully by matching up properties.