Electronegativity

Question 1

What do Pauling electronegativity values indicate?

Answer 1

The difference gives a good indication of the type of bonding-
Large differences= ionic
Smaller differences= covalent

Question 2

What is a permanent dipole?

Answer 2

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

Question 3

What is a polar covalent bond?

Answer 3

A covalent bond with a permanent dipole

Question 4

Why are some molecules more polar than others?

Answer 4

They have a greater difference in electronegativity and so have a greater permanent dipole

Question 5

Will a covalent bond between 2 atoms of the same element be polar?

Answer 5

No as there is no difference so no permanent dipole

Question 6

What is the strength of the polarity of C-H and why?

Answer 6

Low polarity as carbon and hydrogen have similar electronegativities

Question 7

Why are some molecules polar?

Answer 7

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.

Question 8

Why are some molecules non-polar?

Answer 8

Either…

1. They have no polar covalent bonds
2. They have no overall permanent dipole due to the symmetrical arrangement of the polar covalent bonds so the dipoles cancel out

Question 9

What are the differences between bonds and forces?

Answer 9

Bonds- strong attractions

Forces- weak attractions

Question 10

What are intermolecular forces?

Answer 10

Weak attractions between different molecules

Question 11

What are permanent dipole dipole forces?

Answer 11

Weak intermolecular forces between permanent dipoles of polar molecules
(Strength increases with strength of permanent dipoles)

Question 12

What are London forces?

Answer 12

The weak intermolecular attractions between induced dipoles of different nonpolar molecules

Question 13

How are induced dipoles formed and then induced dipole dipole attractions?

Answer 13

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.

Question 14

If the intermolecular force is strong what does this mean?

Answer 14

More energy is required to break them

So have a higher melting and boiling point and therefore a lower volatility

Question 15

What is a hydrogen bond?

Answer 15

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.

Question 16

What is the strength of the hydrogen bonds?

Answer 16

Strong compared to other intermolecular forces yet weaker than bonds

Question 17

Why is water anomalous?

Answer 17

1. Relatively high melting and boiling point due to hydrogen bonds being relatively strong
2. 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

Question 18

What are solvents?

Answer 18

Covalent molecules in liquid state they are either polar or non polar

Question 19

What do polar solvents readily dissolve and why?

Answer 19

They dissolve other polar molecules as can form ion-dipole attractions due to have strong permanent dipoles

Question 20

What will non polar solvents readily dissolve and why?

Answer 20

Non-polar molecules as they have no permanent dipoles

Question 21

When will and ionic solution form?

Answer 21

If the ion-dipole attractions are stronger than the ionic bonds within the solid of the ionic compound

Question 22

What happens to the positive ions in a polar solvent?

Answer 22

They form ion-dipole attractions between the full positive charge of the ion and the partially negative charger of the polar molecule

Question 23

What happens to a negative ion in a polar solvent?

Answer 23

They form ion-dipole attractions between the full negative charge of the ion and the partially positive charge of the polar molecule