Electronegativity is defined as an atom’s ability to attract electrons towards it in a chemical bond. There are several different ways of measuring it, the most common being the Pauling scale. Different elements have different electronegativities based on a number of factors such as size and number of protons, neutrons, and electrons. It is often viewed on an electronegativity chart of the elements, where trends and values can easily be seen. The higher the electronegativity, the stronger an atom attracts electrons. We will be exploring the electronegativity trends in the periodic table.
Electronegativity was developed by Linus Pauling, who won the Noble prize twice. Pauling set the definition of electronegativity as “the power of an atom in a molecule to attract electrons to itself”. He did not come up with the concept, which was introduced by Jöns Jacob Berzelius in 1811, but he did develop a measurable scale, circa 1935.
There are a variety of factors that affect the electronegativity of an atom. Size is an important element of electronegativity. The positive protons in the nucleus “pull” on the negative electrons in the orbitals. The bigger the atom, the larger the distance, and the less effectively the protons are able to pull on the electrons. This leads to larger atoms with more electron shells having lower electronegativity. Attraction between protons and electrons means that atoms with a higher atomic number and number of protons have a higher electronegativity.
From left to right across the period table electronegativity increases. This is because of the increased number of protons as the atomic number increase. From top to bottom electronegativity decreases because of the increasing size of the atoms. As a result, Fluorine is considered the most electronegative element while cesium is the least electronegative element. Halogens are considered to have a high electronegativity, while it is low for the alkali metals and alkaline earth metals.
Electronegativity can tell us a lot about how different elements will bond to each other and which type of bond it will be. If the electronegativity difference between the two elements involved in bonding is less than 0.4 then the bond will be nonpolar covalent. If the difference is between 0.4 and 1.7 then the bond is considered polar covalent. And finally, if the difference is greater than 1.7 then the bond will be ionic.
Fluorine is the most electronegative element on the electronegativity chart, followed by oxygen and then chlorine. This has several implications. Firstly, it means that fluorine is always negative when combined with other elements. Secondly, it means that oxygen always has a negative oxidation state, except in the very rare case where it forms a compound with fluorine. This also explains the high reactivity of fluorine, chlorine and oxygen. Fluorine is so electronegative, that it wants to rip an electron off anything it touches.
No, they do not. It is not possible to measure electronegativity values for the noble gases, because they do not readily form bonds with other atoms.
To find the electronegativity of a molecule, you need to find it for each bond. You look at the electronegativity of the two elements in the bond, and you calculate the difference. This will tell you how polar the bond is.
