Electronegativity & Intermolecular forces

Question 1

What is electronegativity?

Answer 1

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

Question 2

What is the most electronegative atom?

Answer 2

Fluorine

Question 3

What is electronegativity dependent on?

Answer 3

• atomic radius of atom (the smaller the greater)
• number of shells the atom has (the fewer the greater)
• more shells = bigger radius = lower EN -

Question 4

How does electronegativity increase on the periodic table?

Answer 4

• increases as you move up and to the right

Question 5

What is meant by a polar bond?

Answer 5

a covalent bond in which there is an unequal share of electrons due to differing electronegativities of the atoms involved

Question 6

How to tell if a molecule is non-polar (symmetrical)

Answer 6

• central atom bonded to same thing
• no lone pairs affecting bond angle

Question 7

How can some molecules have polar bonds but be non-polar molecules?

Answer 7

They are symmetrical and dipoles cancel out

Question 8

What are intermolecular forces?

Answer 8

Forces BETWEEN molecules (only exist in solid simple molecular substances)

Question 9

Are IMFs weaker or stronger than covalent bonds?

Answer 9

weaker

Question 10

What is the order of strength for the 3 types of IMFs?

Answer 10

IDD<PDD<Hydrogen

Question 11

If molecule(s) are non-polar, what will be the only IMF they have between them?

Answer 11

Induced dipole-dipole (exists in all molecules)

Question 12

If molecule(s) are polar, what IMF will occur in addition to IDDs?

Answer 12

• permanent dipole-dipole
• if NOF bonded to H, hydrogen bonds

Question 13

How do induced dipole-dipole forces arise?

Answer 13

• electrons constantly moving means charge distribution can achange at any time
• one side of a molecule could suddenly become more negative (if electrons moved closer to that side)
• induces a temporary dipole due to uneven distribution of electron density

Question 14

How does an induced dipole in a molecule affect neighbouring atoms and their charge spread?

Answer 14

• a temporary dipole in one molecule induces a dipole in another molecule
• there is an attraction between a + on one molecule and a - on a neighbouring molecule

Question 15

What affects the strength of induced dipole-dipole forces?

Answer 15

• size/Mr of molecule (bigger = more forces)
• surface area contact (more SA contact = more forces)
• only compare SA if molecules same size / isomers -

Question 16

How does strength of induced dipole-dipole forces influence melting/boiling points?

Answer 16

the larger the molecule, the stronger the IMFS, the higher the melting/boiling points

Question 17

When and how do permanent dipole-dipole forces occur?

Answer 17

• occurs when molecules are polar (difference in electronegativity between atoms)
• attraction between + on one molecule and - on second molecule

Question 18

When do hydrogen bonds occur?

Answer 18

• in POLAR molecules when hydrogen is bonded to N, O, or F
• lone pair(s) present

Question 19

Why does hydrogen bonding occur?

Answer 19

• NOF are most electronegative atoms
• big difference in electronegativity between these atoms and hydrogen so pulls apir of electrons in bond very strongly towards themselves
• leaves hydrogen nucleus very +
• lone pair of electrons on neighbouring molecule (containg NOF) attracted to H

Question 20

Is hydrogen bonding a type of bond?

Answer 20

No, it is an attractive force between 2 molecules

Question 21

What are the features of a hydrogen bond diagram?

Answer 21

• partial charges on all atoms
• all lone pairs clearly shown
• hydrogen bond shown clearly (drawn linear) between lone pair (NOF) and + H on other molecule

Question 22

Why is ice less dense than water (despite being solid)?

Answer 22

• there are fewer particles of water per unit of volume in solid state than liquid state
• water molecules further apart in ice due to more gaps/spaces
• in liquid, hydrogen bonds broken so less gaps between molecules

Question 23

Why do simple molecular structures have low boiling/melting points?

Answer 23

• there are weak IMFs between molecules which require very little energy to break
• actual value determined by strength of IMFs

Question 24

Why can simple molecular structures not conduct electricity in solid/molten/aqueous state?

Answer 24

• no mobile charged particles

Question 25

Are non-polar molecules generally soluble?

Answer 25

No because they need to form hydrogen bonds to become soluble

• polar dissolves in polar -