Electronegativity

Electronegativity (abbreviation EN; formula symbol χ (Greek Chi)) is a relative measure of the ability of an atom to attract pairs of electrons to itself in a chemical bond. It is determined by the nuclear charge and the atomic radius, among other factors. The electronegativity can therefore be taken as a guide to the polarity and ionic bond character of a bond: The higher the difference in the electronegativity of the bonded elements, the more polar the bond.

Atoms with high electronegativity are also called electronegative, those with low electronegativity are called electropositive. The electronegativity is the larger, the less electrons are missing on the outer shell to the noble gas configuration, because these "gaps" can be filled easily. It therefore generally increases from left to right within an element period as the nuclear charge number becomes higher. Within an element group, it decreases from top to bottom, mainly because the distance to the nucleus is increasing. The attraction of the nucleus to the electrons thus becomes smaller.

Non-metals are more electronegative and therefore prefer to accept electrons. Metals are weakly electronegative and donate electrons. Noble gases have no electronegativity because they are already in a very stable state.

Determination

Various methods exist for determining the EN. The main difficulty is that the EN refers to the behavior of a particular atom in an atomic bond - in a single bond - and not to individual atoms isolated from each other in the gaseous state (such as the ionization energy and electron affinity), and that it depends to a large extent on the type and number of atoms otherwise associated with the atom in question. However, by calculating the electronegativity difference between possible reaction partners, statements can be made about the intensity of activated reactions and the chemical bonding of the resulting substances with the aid of rules of thumb.