Electronegativity Flashcards
What do Pauling electronegativity values indicate?
The difference gives a good indication of the type of bonding-
Large differences= ionic
Smaller differences= covalent
What is a permanent dipole?
Occurs across a covalent bond between 2 atoms with different electronegativity which gives rise to a small charge difference so that the atoms have opposite partial charges
What is a polar covalent bond?
A covalent bond with a permanent dipole
Why are some molecules more polar than others?
They have a greater difference in electronegativity and so have a greater permanent dipole
Will a covalent bond between 2 atoms of the same element be polar?
No as there is no difference so no permanent dipole
What is the strength of the polarity of C-H and why?
Low polarity as carbon and hydrogen have similar electronegativities
Why are some molecules polar?
They have an overall permanent dipole due to a non-symmetrical arrangement of polar covalent bonds so that the bond dipoles do not cancel out.
Why are some molecules non-polar?
Either…
- They have no polar covalent bonds
- They have no overall permanent dipole due to the symmetrical arrangement of the polar covalent bonds so the dipoles cancel out
What are the differences between bonds and forces?
Bonds- strong attractions
Forces- weak attractions
What are intermolecular forces?
Weak attractions between different molecules
What are permanent dipole dipole forces?
Weak intermolecular forces between permanent dipoles of polar molecules
(Strength increases with strength of permanent dipoles)
What are London forces?
The weak intermolecular attractions between induced dipoles of different nonpolar molecules
How are induced dipoles formed and then induced dipole dipole attractions?
Random movement of electrons causes more electrons to move to 1 side of the 1 molecule, this induces a temp dipole. The partially negative charge of this induced dipole repels the neighbouring molecules electrons inducing a temp dipole on the 2nd molecule this leads to an induced dipole-dipole attraction between the temp dipoles.
If the intermolecular force is strong what does this mean?
More energy is required to break them
So have a higher melting and boiling point and therefore a lower volatility
What is a hydrogen bond?
Occurs across a molecule that has either H-N, H-O or H-F bonds and a strong permanent dipole dipole attractions between the partially positive H atom of 1 molecule where the H is bonded to either a partially negative N, O, F and a 2 molecule via the lone pair.
What is the strength of the hydrogen bonds?
Strong compared to other intermolecular forces yet weaker than bonds
Why is water anomalous?
- Relatively high melting and boiling point due to hydrogen bonds being relatively strong
- Solid is less dense than liquid as the solid h2O molecules form 4 hydrogen bonds which hold the molecules apart leading to an open structure
What are solvents?
Covalent molecules in liquid state they are either polar or non polar
What do polar solvents readily dissolve and why?
They dissolve other polar molecules as can form ion-dipole attractions due to have strong permanent dipoles
What will non polar solvents readily dissolve and why?
Non-polar molecules as they have no permanent dipoles
When will and ionic solution form?
If the ion-dipole attractions are stronger than the ionic bonds within the solid of the ionic compound
What happens to the positive ions in a polar solvent?
They form ion-dipole attractions between the full positive charge of the ion and the partially negative charger of the polar molecule
What happens to a negative ion in a polar solvent?
They form ion-dipole attractions between the full negative charge of the ion and the partially positive charge of the polar molecule
