Electronegativity

Question 1

What is electronegativity?

Answer 1

The ability of an atom to attract the bonding electrons in a covalent bond

Question 2

What three things is an atom’s electronegativity affected by?

Answer 2

1) Nuclear Charge
2) Size of an atom
3) Location of shared pair of electrons

Question 3

How is electronegativity measured?

Answer 3

The Pauling scale

Question 4

What do large values on the Pauling scale indicate?

Answer 4

Atoms are very electronegative

Question 5

What bond type is an electronegativity difference of 0 for?

Answer 5

A pure covalent bond

Question 6

What bond type is an electronegativity difference of 0-1.8 for?

Answer 6

A polar covalent bond

Question 7

What bond type is an electronegativity difference of 1.8< ?

Answer 7

Ionic bond

Question 8

What collection of molecules have pure covalent bonds?

Answer 8

Diatomic molecules

Question 9

Why are hydrocarbons non-polar molecules?

Answer 9

C and H have very similar electronegativity values so there is an even distribution of electrons

Question 10

What four elements are most electronegative?

Answer 10

Nitrogen, Oxygen, Fluorine, Chlorine

Question 11

Where are the most electronegative elements?

Answer 11

Furthest right and furthest up the periodic table (excluding noble gases)

Question 12

What characteristic does a non-polar molecule have?

Answer 12

It’s molecule is symmetrical so the dipoles in either direction cancel out

Question 13

What are intermolecular forces?

Answer 13

The forces between molecules

Question 14

What is a simple molecular lattice?

Answer 14

Molecules held in arrangement by weak forces

Question 15

What forces are the weakest?

Answer 15

London forces

Question 16

What forces are the second weakest?

Answer 16

Permanent dipole-dipole interactions

Question 17

What forces are the strongest?

Answer 17

Hydrogen bonds

Question 18

What is the permanent dipole-dipole interactions between?

Answer 18

A partially positive charged atom of one molecule and a partially negative charged atom of another molecule

Question 19

What molecule demonstrates dipole-dipole interactions?

Answer 19

HCl

Question 20

Are London forces instantaneous?

Answer 20

Yes - they are always changinf

Question 21

Why are London forces weak?

Answer 21

They are only slightly charged at any point

Question 22

What do instantaneous dipoles induce in neighbouring molecules?

Answer 22

Induced dipoles

Question 23

What two types of molecules can London forces occur between?

Answer 23

1) non-polar molecules
2) non-polar with permanent dipoles

Question 24

How does a molecules london forces change when there is an increasing number of electrons? Why?

Answer 24

They increase as there are more induced dipoles

Question 25

How would stronger london forces affect the boiling/ melting point?

Answer 25

Increases them as more energy is needed to overcome them

Question 26

How is the negative charge around a covalent bond distributed?

Answer 26

Not evenly

Question 27

How does electronegativity vary across a period?

Answer 27

It Increases along a period as the atomic radius decreases and charge density increases.

Question 28

How does electronegativity vary down a group?

Answer 28

It decreases - shielding increase so atomic radius increases so charge density decreases

Question 29

How can polar molecules with a permanent dipole align?

Answer 29

To form a lattice of molecules similar to an ionic lattice

Question 30

Why do straight chain molecule’s experience stronger London forces?

Answer 30

They can pack closer together, reducing the distance over which the force acts, making it stronger

Question 31

Why do longer alkane chains have higher boiling points?

Answer 31

They have a larger Mr, so stronger London forces between chains

Question 32

Why does branching of alkane chains cause for weaker London forces?

Answer 32

The chains are less able to pack tightly together so the distance the forces act is increased and the attractive forces are weakened - lower boiling point.

Question 33

What do hydrogen bonds act between? (Exclusively)

Answer 33

Between hydrogen and either nitrogen, oxygen or fluorine (most electronegative atoms)

Question 34

How is a hydrogen bond demonstrated in a diagram?

Answer 34

A dotted line

Question 35

Why does ice have a Lower density than liquid water?

Answer 35

The hydrogen bonds hold the molecules in a rigid structure with a lot of air gaps

Question 36

Why are water and alcohols not good at dissolving polar molecules?

Answer 36

Some can’t form hydrogen bonds