Electronegativity mmm…electrons Fluorine.

Electronegativity is the measure of the ability of an atom in a molecule to attract electrons to itself.

TREND increases from left to right across a period and decreases down a group.

Why? Attraction experienced by an electron towards a particular nucleus depends on: Number of protons in nucleus Atomic radius Amount of electron screening Why increased EN across period? REASON: Number of protons in the nucleus increases = increased electron attraction towards nucleus REASON: decreased atomic radius= increased electron attraction towards nucleus Why decreased EN down a group? REASON: Atomic radius increases down the group= decreased electron attraction towards nucleus REASON: Increased electron shielding down the group = decreased electron attraction towards nucleus

Exceptions Gallium and germanium have higher EN than aluminum and silicon Elements in the 6th period to the 12th period (transition metals) increase EN down the group.

Possible explanations Due to phenomenon called d-block contraction, the addition of full a d-orbital decreases the atomic radius to size close to 3rd period size Reason why Ga is smaller than Al and thus more EN Certain transition metals have unusually small atomic radii because the d-electrons are not as effective in shielding outer electrons from the increasing positive nucleus

Usage? Fake trend. Sorry.

Electronegativity is a relative scale used to determine polarity and ionic character of bonds Not based on a measurable scale Pauling scale commonly used F = 4.0 Cs= 0.7 the difference in electronegativities more important than individual values small difference between electronegativities of elements in a compound = low polarity Large difference electronegativities = very polar

The B—F bond is more polar because > for the B—F than the B—Cl Example Ex: What would have a more polar bond: B—F or B—Cl ? Solution: The B—F bond is more polar because > for the B—F than the B—Cl

Polarity and Ionic character As increases, the ionic character of the bond also increases Small yields a more covalent bond Larger yields a more ionic bond

El Fin.