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Chemistry 2.4

AS edexcel chemistry - bond polarity

What is electronegativity? A measure of the tendency of an atom to draw a pair of electrons from a covalent bond towards itself.
What is electronegativity measured by? Pauling scale - arbitrary units. Fluorine is the most electronegative element, caesium is the least
Where are electrons positioned in a polar vs non polar bond? In a covalent bond between 2 atoms of same element, average position of e- is half way between atoms. In a covalent bond between 2 atoms of different electronegativities, localised around 1, polar, ionic character, distortion of e- cloud, partial charges
What is a dipole moment? a measure of net molecular polarity and charge separation - measures the polarity of a bond
What are the properties of polarising and polarisable atoms? Polarising - high charge density, high charge and small atomic radius. Polarisable - high charge, large atomic radius
Why is a symmetrical molecule with polar bonds non-polar? Dipoles cancel. A polar molecule must be asymmetrical with polar bonds
Why are polar molecules water soluble? The partial charges on the polar molecule are attracted to the partial charges on the dipolar water molecules
What is meant by the continuum of bonding? Covalent and ionic are two extremes. There can be ionic with covalent character caused by polarisation of anion, and covalent with ionic character caused by polar bonds
What are the trends in electronegativity? - metals are less electronegative than non metals - electronegativity increases across a period due to increasing charge density - electronegativity decreases down group due to decreasing charge density
Why don't noble gases have electronegativity values? They rarely form covalent bonds
How do you test for polar molecules? Run a stream of liquid from a burette next to a rod that has been rubbed with wool and charged with static electricity, polar moelcules are attracted to high charge of the rod and the jet of liquid is deflected
Created by: 11043