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Chemistry 2.4
AS edexcel chemistry - bond polarity
Question | Answer |
---|---|
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 |