Electronegativity - OZ Flashcards
Are covalent bond electrons shared evenly
No as some atoms have a stronger pull
Electronegativity definition
Electronegativity is the power of the atom to attract the bonding electrons in a covalent bond to itself
Which areas of the periodic table have the highest and lowest electronegativity
Lowest - bottom of group, lower periods
Highest - top of group, higher periods
Does electronegativity increase or decrease across a period and why
Increase because each atoms has one more proton in its nucleus. There is also an extra electron but they are going into the same shell so they don’t sheild each other from this extra positive charge in the nucleus, so the nucleus attracts the bonding electons more strongly
Does electronegativity increase or decrease down a group and why
Decrease because each atom has an extra shell of electrons, so the bonding electrons are further from the nucleus and more shielded from its positive charge, so attracted less by the nucleus
What are the 4 most electronegativite elements
Florine, oxygen, nitrogen, chlorine
(FONCL)
What does it mean when there is a big difference in electronegativity
Complete electron transfer so it is ionic bonding, e.g. NaCl
What does it mean when there is a small difference in electronegativity
Polar covalent bonding and electrons are transfered but not evenly, e.g. HCl, H20
What does it mean when there isn’t a difference in electronegativity
Electrons are evenly shared so it is pure covalent bonding, e.g. Cl2, H2, N2
What are polar covalent bonds
There are covalent bonds but where the electron pair is not evenly shared as the 2 bonding atoms are not equal in electronegativity (but not hugely different or the compound would be ionic)
Polar covalent bonds - H - Cl describe what is happening in terms of electrons
Cl is more electronegativitie than H so it has a stronger pull on the shared electrons. This makes the bond polar. The chlorine becomes slightly negative (delta minus) and the H slightly positive (delta plus)
How to make a covalent bond more polar
make the difference in electronegativity bigger
H-F, H-Cl, H-Br, H-I = which is most polar and which is least
H-F is most polar as it has the biggest difference in electronegativity
H-I is least polar as it has the smallest difference in electronegativity
When does a molecule not have an overall dipole
when a molecule contains polar bond but are non-polar overall, which happens if the bonds are arranged symmetrically so the dipoles cancel
How to know if a molecule has an overall dipole
draw the molecules shape (bent, linear, tetrahedral etc) and see if there is a way for there to be a positive and negative dipole at opposite sides.
https://chem.libretexts.org/@api/deki/files/125401/151611849161611773.jpg?revision=1
Intermolecular forces definition
weak forces holding simple molecules together which are broken when heat is applied causing state changes
In which bonding are intermolecular forces found
only in simple covalent bonding not ionic, metallic or giant covalent lattices
What are the 3 types of intermolecular forces
Instantaneous dipole induced dipole (IDID’s), Permanent dipole - permanent dipole (PDPD), Hydrogen bonding
Instantaneous dipole induced dipole (IDID’s) - How does this occur
they happen due to the random movement of electrons in a molecule creating a temporary and instantaneous dipole, this will then induce a dipole in a neighbouring molecule as opposite poles attract
Instantaneous dipole induced dipole (IDID’s) - Criteria
having electrons so molecules
Permanent dipole - permanent dipole (PDPD) - How does this occur
When the partially positive of one molecule attracts the partially negative part of a neighbouring molecule
Permanent dipole - permanent dipole (PDPD) - Criteria
2 polar molecules both with 2 polar charges and an overall dipole
Hydrogen bonding - How does this occur
When H is directly bonded to F/O/N on molecule 1 and a lone pair on F/O/N on molecule 2
https://cdn.kastatic.org/ka-perseus-images/2ac0bbc48423e179715a9ba533d0dcb8f2fd45c3.png (hydrogen covalent bond must be 180 degrees from intermolecular force)
Why is hydrogen bonding so strong
as F, O and N all have a very high electronegativity which makes the H unusually partially positive, the lone pair on F, O and N will attract this partially positive H very strongly
How to know which molecule is stronger if they only have IDID’s
by the size of the molecule because this means there are more electrons
or the shape of the molecule - if they are more linear the molecules can et closer together which means they can from stronger IDID’s
