OZ - Electronegativity Flashcards
What is electronegativity?
The ability of an atom to attract the binding electrons in a covalent bond.
What is electronegativity usually measured using?
The Pauling scale.
What does the size of the electronegativity value suggest about the electronegativity of the element?
The higher the electronegativity value, the more electronegative the element.
What is the most electronegative element?
Fluorine - has a value of 4 on the Pauling scale.
Apart from fluorine, what other elements are also very strongly electronegative?
Oxygen, chlorine and nitrogen.
How high is the value of the most electronegative element?
4.0
How low is the value of the least electronegative element?
Around 0.7
How does electronegativity change across the periodic table?
It increases as you move towards fluorine.
How does electronegativity change across periods?
Increases.
How does electronegativity change down groups?
Decreases (ignoring the noble gases).
What might covalent bonds be polarised by?
Difference in electronegativity.
In covalent bonding, where do the bonding electrons sit?
In orbitals between 2 nuclei.
When will covalent bonds be non-polar?
If both atoms have similar or identical electronegativities and so the electrons will sit roughly midway between the 2 nuclei and the bond will be non-polar.
In what molecules will covalent bonds be non-polar and why?
In homonuclear, diatomic gases (e.g. H2 and Cl2) because the atoms have equal electronegativities and so the electrons are equally attracted to both nuclei.
When will covalent bonds be polar?
If the bond is between 2 atoms with different electronegativities making the bonding electrons get pulled towards the more electronegative atom. This causes the electrons to be spread unevenly and so there will be a charge across the bond (each atom has a partial charge - one atom is slightly positive and the other is slightly negative).
How do you work out if a bond is polar or not?
By using the Pauling scale:
Find the difference between the electronegativity values given for each atom in the bond. The bond is polar if the difference in electronegativity values is more than about 0.4.
What difference in electronegativity value using the Pauling scale shows a polar bond?
The bond is polar if the difference in electronegativity values is more than about 0.4.
In a polar bond, what does the difference in electronegativity between the 2 atoms cause?
A dipole.
What is a dipole?
A difference in charge between the 2 atoms caused by a shift in electron density in the bond.
What is a dipole caused by?
A shift in electron density in the bond.
Finish this sentence with the effects on electron density and and the polarity of the bond:
The greater the difference in electronegativity…
…the greater the shift in electron density, and the more polar the bond.
Whether a molecule is polar or not depends on what?
Its shape and the polarity of its bonds.
What does a polar molecule have?
An overall dipole, which is just a dipole caused by the presence of a permanent change across the molecule.
What is an overall dipole?
A dipole caused by the presence of a permanent charge across the molecule.
What might an overall dipole also be referred to as?
‘Overall polarity’.
If the polar bonds are arranged so they point in opposite directions, does it mean the molecule is polar or not?
Non-polar as they’ll cancel each other out.
If the polar bonds are arranged so they all point in roughly the same direction, does it mean the molecule is polar or not?
Polar.
