Topic 2: Bonding

Question 1

Define Ionic Bonding

Answer 1

the strong electrostatic attraction between the oppositely charged ions

Question 2

what does charge density depend on?

Answer 2

ionic charge and ionic radius

Question 3

what is proof for the existence of ions

Answer 3

migration of ions and physical properties

Question 4

migration of ions example

Answer 4

Copper (II) Chromate
copper 2+ ions migrate to negative electrodes (blue)
chromate ions migrate to the positive electrode (yellow)

Question 5

define covalent bonding

Answer 5

the strong electrostatic attraction between the shared pair of electrons and the nuclei of the atoms bonded

Question 6

what is dative covalent bonding

Answer 6

instead of one electron coming from each atom, the electrons come from a single atom

Question 7

below which period in the periodic table can atoms expand their octet

Answer 7

below period 2

Question 8

define bond energy

Answer 8

measure of how strong a bond is

Question 9

what does a double bond consist of?

Answer 9

a sigma bond and pi bond between 2 atoms

Question 10

angle in a tetrahedral molecule

Answer 10

109.5

Question 11

angle in a pyramidal molecule

Answer 11

107

Question 12

angle in a bent molecule

Answer 12

104.5

Question 13

define electronegativity

Answer 13

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

Question 14

what are London forces

Answer 14

when a temporary dipole is attracted to an induced dipole

Question 15

define metallic bonding

Answer 15

strong electrostatic attraction between metal ions and the delocalised electrons

Question 16

tetrachloromethane, CCl₄, contains polar bonds but is not a polar molecule, why?

Answer 16

the centres of charges are in the same place therefor it is non polar

Question 17

explain why the melting temp of magnesium is much higher than that of sodium

Answer 17

magnesium ion has a larger charge density
magnesium ions are smaller than sodium ions
magnesium ions have more delocalised electrons
magnesium ions have a greater attraction for the delocalised sea of electrons

Question 18

the electrical conductivity of pure silicon is very low. explain why this is in terms of the bonding.

Answer 18

silicon’s outer electrons are fixed in covalent bonds

therefore silicons electrons are not free to move

Question 19

explain why sulphur forms an expanded octet but oxygen does not

Answer 19

to expand the octet an electron as to be promoted to a higher energy level
for sulfur the next energy level is fairly close, for oxygen the energy jump is too large

Question 20

describe the shape of TeF₆

Answer 20

octahedral. 90 degree angle

Question 21

describe the shape of AsF₅

Answer 21

trigonal bipyramidal. 120 and 90 degrees

Question 22

describe the shape of PH₃

Answer 22

trigonal pyramidal. 107.5 degrees

Question 23

state and explain whether you would expect magnesium fluoride to have a higher or lower melting point than magnesium oxide

Answer 23

magnesium fluoride has lower
fluoride has a lower charge than oxide
less energy needed to overcome/ break bonds

Question 24

suggest why copper (II) chromate ions dissolve in water

Answer 24

ions are hydrated

Question 25

state and explain the trend in ionic radius from K+ to Ti4+

Answer 25

ionic radius decreases ions are isoelectronic nuclear charge increases attraction between electrons and nucleus increases

Question 26

aluminium fluoride (AlF₃) melts at a much higher temp than either aluminium bromide or aluminium chloride, but none of the compounds conduct electricity when molten. compare the structure and bonding present in the three compounds. (4)

Answer 26

AlF₃ bonding is covalent structure is giant other bonding is covalent structure is simple molecular

Question 27

explain why hydrogen halides are gases at room temp

Answer 27

bp lower than room temp weak intermolecular forces little energy needed to overcome the forces between the molecules

Question 28

explain why less energy is needed to break the covalent bond in hydrogen iodide than in hydrogen bromide (3)

Answer 28

iodine atoms are larger than bromine atoms bond is longer in HI than HBr attraction between nuclei and shared pair of electrons is weaker

Question 29

state and explain the trend in bond polarity in the hydrogen halides as atomic number of the halogen increases

Answer 29

bond polarity decreases with atomic number halogen atom becomes less electronegative smaller difference in electronegativity between H and halogen

Question 30

explain why the F-P-F bond angle in PF₃ (107) is different to the F-Si-F bond angle in SiF₄ (109.5)

Answer 30

electron pair repulsion pushing bonds closer together | lone pairs repelling more than bonding pairs (PF₃)

Question 31

Explain why CH₄ molecules are tetrahedral and state the H-C-H bond angle

Answer 31

electron pairs repel shape provides minimum repulsion angle is 109.5

Question 32

Explain why the H-O-H bond angle in water is smaller than the H-N-H bond angle in NH₃

Answer 32

water has one more lone pair of electrons than NH₃ lone pairs repel more than bonding pairs bonding pairs are pushed closer

Question 33

explain why HF has a higher melting point than HCl

Answer 33

HF forms hydrogen bonds HCl only forms London forces hydrogen bonds are stronger

Question 34

explain why HF dissolves better in water than hexane

Answer 34

both involve breaking hydrogen bonds (between HF molecules) hydrogen bonds are reformed when HF dissolves in water only London forces formed when HF dissolves in hexane

Question 35

describe how HF molecules form London forces

Answer 35

``` random movement of electrons temporary dipole forms induced dipole (in adjacent molecules) ```

Question 36

explain why CH₃CH₂CH₂CH₃ has a higher boiling point than (CH₃)₃CH

Answer 36

branched alkane/ (CH₃)₃CH has weaker London forces | molecules have lower SA/ cant be as close together

Question 37

why are alkanes insoluble in water

Answer 37

they cant form hydrogen bonds

Question 38

Explain why methanethiol (CH₃SH) cant form hydrogen bonds

Answer 38

sulphur is less electronegative than oxygen | S-H bond is not polar enough (to attract S: from another molecule)

Question 39

state and explain which of methanol and methane is more volatile

Answer 39

methane cant form hydrogen bonds hydrogen bonds are stronger (than London forces)

Question 40

Explain why methanol molecules are polar and describe a lab test to prove it

Answer 40

(C-O and) O-H bonds polar not symmetrical test: charged object near jet of methanol result: jet deflected

Question 41

describe the hydration of the chloride ions formed when HCl dissolves in water

Answer 41

partial positive H atom of water (1) is attracted to (full) negative charge of chlorine ions

Question 42

suggest why HCl dissolves well in methylbenzene (C₇H₈)

Answer 42

similar intermolecular forces | London forces

Question 43

why is ice less dense than water?

Answer 43

more open/more space between molecules (making it less dense) due to (3 Dimensional) lattice/ ring structure in ice hydrogen bonds longer than the covalent bonds

Question 44

Aluminium fluoride and aluminium chloride are both crystalline solids at room temperature. Aluminium fluoride sublimes to form a gas at 1291qC (1564 K), whilst aluminium chloride sublimes at 178qC (451 K). Use the Pauling electronegativity values in the Data Booklet to explain these differences in sublimation temperature.

Answer 44

``` aluminium and chlorine electronegativity difference 1.5 AND aluminium and fluorine electronegativity difference 2.5 aluminium chloride (mostly) covalent / (small) molecule aluminium fluoride (bonds) more polar aluminium chloride molecular so weak(er) intermolecular forces / London forces aluminium fluoride is a giant structure/ strong electrostatic forces of attraction between the ions more energy needed to break the stronger bonds to cause sublimation in aluminium fluoride ```