6.2 Electronegativity and polarity Flashcards
When bonded atoms are different elements what happens?
-The nuclear charges are different
-Atoms may be different sizes
-The shared pair of electrons may be closer to the nucleus than the other
-The shared pair of electrons may experience more attraction from one of the bonded atoms than the other
-This is called electronegativity
Define electronnegativty
A measure of the attraction of a bonded atoms for the pair of electrons in a covalent bond
What is the most electronegative element
F, fluorine
What scale is used to compare electronnegativity?
Pauling scale
How does electronegativity change across and up the the periodic table
-Electronegativity increases across the periodic table
-Electronegativity up the periodic table
What are the electronegativity values used to estimate the type of bonding?
In a non-polar bond how is the electron pair shared?
-The bonded electron pair is shared equally between the bonded atoms
When is a bond polar?
When the bonded atoms are the same or the bonded atoms have the same or similar electronegativity (eg. hydrogen and carbon)
Define polar covalent bond
A bond with permanent dipole, having positive and negative partial charges on bonded atoms
Define polar molecule
A molecule with an overall dipole, having taken into account any dipoles across bonds and the shape of the molecule
What is a permanent dipole?
A small change difference that does not change across a bond, with positive and negative partial charges on the bonded atoms as a result of the bonded atoms having different electronegativities
Explain how hydrogen chloride (HCl) is a polar molecule
-The chlorine atom is more electronegative than the hydrogen atom
-The chlorine atom has a greater attraction for the bonded pair of electrons than the hydorgen atom, resulting in a polar covalent bond
-The hydrogen atom has a small partial positive charge (δ+)
-The chlorine atom has a small partial negative charge (δ-)
Explain why a CO2 molecule is non-polar
-The two C=O bonds have a permanent dipole
-The two dipoles act in opposite directions and exactly oppose one another
-Over the whole molecule the dipoles cancel out and the overall dipole is 0
Explain why H20 is polar
-The two O-H bonds each have a permanent dipole
-The two dipoles act in different directions but do not directly oppose each other
-Overall the oxygen end of the molecule has a δ- charge and the hydrogen end of the molecule has a δ+ charge
Explain how sodium chloride (NaCl) is dissolved by water to form aq Na and Cl ions
-Water molecules attract Na+ and Cl- ions
-The ionic lattice breaks down as it dissolves
-Water molecules surround the Na+ and Cl- ions
-Na+ ions are attracted towards the oxygen of the water (δ-)
-Cl- ions are attracted towards the hydrogen of the water (δ+)
Define dipole
A separation in electrical charge so that one atom of a polar covalent bond, or one end of a polar molecule has a small positive charge δ+ and the other has a small negative charge δ-
What other exception is there where the molecule is not polar but has regions of electronegativity?
CO2, NF3
