2 - structure and bonding

Question 1

(2)

ionic bond

Answer 1

• a strong electrostatic force of attraction
• between two oppositely charged ions

Question 2

when are ionic bonds stronger/melting point higher?

Answer 2

when the ions are smaller or have higher charges

Question 3

are positive ions bigger or smaller than their atoms and why?

Answer 3

smaller - it has one less shell of electrons so there is a greater net force holding them closer

Question 4

are negative ions bigger or smaller than their atoms and why?

Answer 4

bigger - the pull of the nucleus is shared over more electrons ∴ attraction per electron is less

Question 5

does ionic radii increase or decrease going down the group?

Answer 5

increase - as you go down the ions have more shells of electrons

Question 6

(3)

physical properties of ionic compounds:

Answer 6

• high melting points - strong attractive forces
• conduct electricity when in solution/molten - ions are free to move
• brittle

Question 7

(2)

covalent bond

Answer 7

• an electrostatic attraction
• between two nuclei and a shared pair of electrons

Question 8

(3)

why do nuclei joined by multiple bonds have a greater electron density?

Answer 8

• there are more shared electrons between atoms
• which increases the electron density
• which causes a greater force of attraction ∴ a shorter bond length and greater bond strength

Question 9

(1)

dative covalent bond

Answer 9

• when the shared pair of electrons in the covalent bond come from one of the bonding atoms

Question 10

how do you demonstrate a dative bond in a diagram?

Answer 10

with an arrow →

Question 11

linear

Answer 11

2 bonding pairs
0 lone pairs
180°
eg. CO2, BeF2

Question 12

trigonal planar

Answer 12

3 bonding pairs
0 lone pairs
120°
eg. BF3, AlCl3

Question 13

tetrahedral

Answer 13

4 bonding pairs
0 lone pairs
109.5°
eg. SiCl4, NH4+

Question 14

trigonal pyramidal

Answer 14

3 bonding pairs
1 lone pair
107°
eg. ClO3, H30+

Question 15

bent

Answer 15

2 bonding pairs
2 lone pairs
104.5°
eg. SCl2, OF2

Question 16

trigonal bipyramidal

Answer 16

5 bonding pairs
0 lone pairs
120° and 90°
eg, PCl5

Question 17

octahedral

Answer 17

6 bonding pairs
0 lone pairs
90°
eg. SF6

Question 18

if there are lone pairs, how many degrees will the bond angle decrease by? (if ykwim)

Answer 18

2.5° per lone pair

Question 19

(2)

electronegativity

Answer 19

• the tendency of an atom in a covalent bond
• to attract electrons to itself

Question 20

how do you measure electronegativity?

Answer 20

pauling scale

Question 21

(3)

does electronegativity increase or decrease across a period?

Answer 21

• increases
• number of protons increases,
• atomic radius decreases ∵ the electrons in the same shell are pulled in more

Question 22

(3)

does electronegativity increase or decrease down a group?

Answer 22

• decreases
• the distance between the nucleus and the outer shell increases
• the shielding of the inner shell electrons

Question 23

a compound that has a small electronegativity difference is..?

Answer 23

purely covalent

Question 24

a compound that has a very large electronegativity difference is..?

Answer 24

ionic

Question 25

when does a polar covalent bond form?

Answer 25

when the elements have different electronegativities

Question 26

# (2) what does a polar covalent bond have?

Answer 26

- an unequal distribution of electrons - which produces a dipole (or charge separation)

Question 27

# (2) will a symmetric molecule be polar?

Answer 27

- it will not be polar even if the individual bonds ARE polar - the dipoles will cancel out; there is no NET dipole moment

Question 28

example of a symmetrical molecule that has polar individual bonds but is a non-polar molecule?

Answer 28

CO2

Question 29

when do london forces occur?

Answer 29

between all simple covalent molecules (NOT IN IONIC SUBSTANCES)

Question 30

# (3) explain london forces

Answer 30

- the electrons are moving constantly and randomly - electron density fluctuates and temporary dipoles form - can cause dipoles in neighbouring molecules (induced dipoles)

Question 31

# (2) do straight chain alkanes have stronger london forces than branched alkanes?

Answer 31

- stronger - they have a larger surface area of contact between molecules compared to branched alkanes

Question 32

# (3) facts about permanent dipole-dipole forces

Answer 32

- between polar molecules & have a permanent dipole - stronger than london forces - polar molecules are asymmetrical where there is a difference in electronegativity

Question 33

# (3) when does hydrogen bonding occur?

Answer 33

- in compounds that have a hydrogen atom attached to one of the three most electronegative atoms (nitrogen, oxygen and fluorine) - there is a LARGE electronegativity difference - occurs in addition to london forces

Question 34

# (4) what can form hydrogen bonds?

Answer 34

- alcohols - carboxylic acids - protein - amides

Question 35

can hydrogen bonding cause high boiling points?

Answer 35

yes, anomalously high (H20, NH3, HF)

Question 36

square planar

Answer 36

4 bonding pairs 2 lone pairs 90° eg. XeF₄