Polarity Flashcards
Electronegativity
The ability of an atom to attract the bonding electrons in a covalent bond
What measures electronegativity?
The Pauling scale
What element has the highest electronegativity?
Fluorine
What causes an atom of an element to have high electronegativity?
If it has higher nuclear charge but small atomic radius
Trend in electronegativity across the periodic table
Decreases down the group
increases across the period
What can happen to covalent bonds if there is a different in electronegativity across the atoms?
The bond can be polarised
What causes a polar bond?
When atoms of 2 different electronegativities bond, the bonding electrons are pulled to more electronegative atom
Thus electrons spread unevenly in the bond = an opposite charge at different ends
How are differences in charge across a polar bond shown?
More electronegative element is slightly negative (d-) because bonded electrons are attracted more strongly to it
Less electronegative element is slightly positive (d+) because bonded electrons drawn away from it
=opposite charges at ends of molecule
How is a polar covalent bond shown?
An arrow from the positive charged atom to negative charged atom to represent electrons moving away to mor electronegative element
What is the difference in charge across the 2 atoms called?
A dipole
Dipole
A difference in charge between 2 atoms caused by a shift in electron density in the bond, separated by a small distance
What causes a greater polar bond?
A larger difference in electronegativity across the molecule because there is a greater shift in electron density
What covalent bonds are non polar?
When atoms of the same element bond so no difference in electronegativity
Or if the atoms of the elements electronegativity is so small it is essentially non polar
Where do electrons sit in the covalent bond if the bond isn’t polar?
Midway because they area attracted the same amount to both atoms
What are the extremes on the continuum of bond types?
Purely ionic character
Purely covalent
Where do polar bonds lie in the continuum of bond type?
In the middle, neither purely covalent or ionic dependent on the difference in electronegativity
In a polar bond, what causes a higher % of ionic character?
If the difference in electronegativity (on the Pauling scale) between 2 atoms of different elements is much higher
Because this shows a greater shift in electron density thus more polar bond
In a polar bond, what causes a lower % of ionic character?
If the difference in electronegativity (on the Pauling scale) between 2 atoms of different elements is low
Because this shows a lesser shift in electron density thus less polar bond
What bonds can be purely covalent?
Atoms of single elements eg diatomic gases eg Cl2
Because the electronegativity difference is 0 thus bond isn’t polar and there is no shift in electron density = no dipole
How to find the % ionic character of a bond?
Find the electronegativities of each element in the bond
Find the difference between these
Correlate this number in the table given to find % ionic character
If a molecule has polar bonds does that make the molecule a polar molecule?
Not necessarily
What determines if a molecule is considered polar?
If the molecule contains polar bonds and has a certain shape where the dipoles are not cancelled out
How shape effects the overall polarity of a molecule
The molecule must have an overall dipole acting in the same direction so the dipoles reinforce each other
How can a molecule have polar bonds but not be overall a polar molecule?
If the polar bonds act in opposite directions to each other = cancels out so no overall dipole