Presentation on theme: "Electronegativity Fluorine. mmm…electrons. Electronegativity is the measure of the ability of an atom in a molecule to attract electrons to itself."— Presentation transcript:
Electronegativity Fluorine. mmm…electrons
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? 1.Attraction experienced by an electron towards a particular nucleus depends on: a)Number of protons in nucleus b)Atomic radius c)Amount of electron screening 2.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 3.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 1.Gallium and germanium have higher EN than aluminum and silicon 2.Elements in the 6 th period to the 12 th period (transition metals) increase EN down the group.
Possible explanations 1.Due to phenomenon called d-block contraction, the addition of full a d-orbital decreases the atomic radius to size close to 3 rd period size Reason why Ga is smaller than Al and thus more EN 2.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
Example Ex: What would have a more polar bond: BF or BCl ? Solution: The BF bond is more polar because > for the BF than the BCl
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