Electronegativity and Polarity

Electronegativity is a measure of how badly an atom wants to 'hog' the electrons it shares in a bond. Think of it as 'atomic greed.' On the periodic table, electronegativity follows a predictable trend: it increases as you move from left to right and decreases as you move down a group. The 'king' of electronegativity is Fluorine (F), with a value of $4.0$, while elements like Cesium are at the bottom with values around $0.7$. When two atoms bond, the one with the higher value pulls the shared electrons closer to its own nucleus.

When atoms share electrons, we call it a covalent bond. However, if the atoms have different 'greed' levels, the sharing is unequal. We calculate the difference in electronegativity ($\Delta EN$) to determine the bond type. If the difference is small ($< 0.5$), it is a nonpolar covalent bond (equal sharing). If the difference is significant ($0.5$ to $1.7$), it is a polar covalent bond (unequal sharing). If the difference is massive ($> 1.7$), the greedier atom steals the electron entirely, creating an ionic bond.

In a polar covalent bond, the 'tug-of-war' isn't a tie. Because electrons are negatively charged, the atom that pulls them closer becomes slightly negative. We use the Greek letter delta ($\delta$) to show these partial charges. The greedier atom is labeled **$\delta^-$ (partial negative), and the atom that is losing the tug-of-war is labeled $\delta^+$ (partial positive). These aren't full charges like in an ion; they are just 'hints' of charge that make the molecule 'sticky' or polar**.