physical chem; bonding

Question 1

define the term ionic bonding

Answer 1

it’s the electrostatic force of attraction between oppositely charged ions formed electron transfer

Question 2

what charge does group 1 form?

Answer 2

1+

Question 3

what charge does group 2 form?

Answer 3

2+

Question 4

what charge does group 3 form?

Answer 4

3+

Question 5

what charge does group 5 form?

Answer 5

3-

Question 6

what charge does group 6 form?

Answer 6

2-

Question 7

what charge does group 7 form?

Answer 7

1-

Question 8

list the molecular ions

Answer 8

OH⁻ = hydroxide
NO₃⁻ = nitrate
NH₄⁺ = ammonium
SO₄²⁻ = sulfate
CO₃²⁻ = carbonate

Question 9

do ionic compounds dissolve in water & if so why?

Answer 9

yes
as water molecules are polar they can attract the +ve & -ve ions & break up the structure

Question 10

explain the features of ionic structures

Answer 10

can conduct electricity when molten or dissolved as e- are free to move around

have high m.p as the structure has many strong electrostatic forces between oppositely charged ions = lots of energy required to overcome the forces

Question 11

what makes an ionic bond stronger & provide an example

Answer 11

when the ions are smaller/have higher charges
e.g. MgO has a higher m.p than NaCl as MgO’s ions are smaller & have higher charges (2+ & 2-) compared to NaCl (1+ & 1-)

Question 12

explain the trend of ionic radii in groups & why

Answer 12

increases down a group as ions have more shells of e- down a group

Question 13

define the term covalent bonding

Answer 13

its an electrostatic attraction between the shared e- & +ve nucleus

Question 14

what is a dative/coordinate bond?

Answer 14

its a bond where 1 atom donates 2 e- to an atom/ion

Question 15

give examples of compound that have dative bonds

Answer 15

NH₄⁺
H₃O⁺
NH₃BF₃

Question 16

give examples of giant covalent structures

Answer 16

graphite
diamond

Question 17

what is a covalent simple molecular structure & give examples

Answer 17

simple molecular - IMF (van der waals, permanent dipoles, H bonds) between molecules

e.g. iodine, ice, CO₂, H₂O & CH₄

Question 18

what is a covalent macromolecular structure & give examples

Answer 18

it’s a giant molecular structure held together by many strong covalent bonds

e.g. diamond, graphite, silicon dioxide & silicon

Question 19

describe the structure of graphite

Answer 19

layers slide easily as there are weak forces between the layers
delocalised e- between layers allow graphite to conduct electricity as they can carry a charge
has low density - as layers are far apart compared to bond length
many strong covalent bonds = high m.p

Question 20

describe the structure of diamond

Answer 20

good heat conductor - has a tightly packed, rigid arrangement
many very strong covalent bonds = high m.p
doesn’t conduct electricity well as doesn’t have any delocalised e-

Question 21

describe the similarities in the structures of graphite & diamond

Answer 21

they both and many strong covalent bonds and are both insoluble due to the strength of their bonds

Question 22

define the term metallic bonding

Answer 22

it’s the electrostatic force of attraction between the metal +ve ions & the delocalised e-

Question 23

what structures do metals have?

Answer 23

giant metallic structures

Question 24

describe the structure of giant metallic lattices

Answer 24

they have +ve metal ions which are formed as metals donate e- to form a sea of delocalised e-

Question 25

describe the features of metallic structures

Answer 25

high m.p - due to strong electrostatic attractions good electrical conductors - delocalised e- are mobile & can carry electrical currents good thermal conductors - delocalised e- can transfer KE are insoluble as metallic bonds too strong to break

Question 26

what makes a metallic bond stronger & provide an example

Answer 26

the more e- an atom can donate to the delocalised e- system = higher m.p e.g. Mg has a higher m.p than Na as Mg can donate 2 e- whereas Na can only donate 1 e-

Question 27

name the structure of a shape & its bond angle with 2 bonding pairs & 0 lone pairs

Answer 27

linear 180º

Question 28

name the structure of a shape & its bond angle with 3 bonding pairs & 0 lone pairs

Answer 28

trigonal planar 120º

Question 29

name the structure of a shape & its bond angle with 4 bonding pairs & 0 lone pairs

Answer 29

tetrahedral 109.5º

Question 30

name the structure of a shape & its bond angle with 5 bonding pairs & 0 lone pairs

Answer 30

trigonal bipyramidal 120º & 90º

Question 31

name the structure of a shape & its bond angle with 6 bonding pairs & 0 lone pairs

Answer 31

octahedral 90º

Question 32

name the structure of a shape & its bond angle with 3 bonding pairs & 1 lone pair

Answer 32

pyramidal 107º

Question 33

name the structure of a shape & its bond angle with 2 bonding pairs & 2 lone pairs

Answer 33

bent 104.5º

Question 34

name the structure of a shape & its bond angle with 4 bonding pairs & 2 lone pairs

Answer 34

square planar 90º

Question 35

define the term electronegativity

Answer 35

it's the ability of an atom to attract a pair of e- in a covalent bond

Question 36

what is the most electronegative atom?

Answer 36

fluorine

Question 37

list the most electronegative atoms

Answer 37

F, O, N & Cl

Question 38

state the general trend of electronegativity in the periodic table

Answer 38

electronegativity increases the further up & right you in the periodic table

Question 39

state the factors that affect electronegativity

Answer 39

nuclear charge: increase in no.of protons = increased electronegativity atomic radius: its the distance between e- & nucleus - increased atomic radius = decreased electronegativity shielding: its the no.of shells & subshells - increased shielding = decreased electronegativity

Question 40

how do covalent bonds become polar?

Answer 40

when atoms attached have a difference in electronegativity

Question 41

how do we know if a compound is polar?

Answer 41

atoms will have either a delta +ve (on least electronegative atom) / delta -ve (on most electronegative atom)

Question 42

how do we know if an atom is non-polar?

Answer 42

if the atoms bonded have the same / similar electronegativities

Question 43

what causes a bond to be more polar?

Answer 43

the bigger the difference in electronegativity = the more polar a bond will be

Question 44

what is the difference between intramolecular & intermolecular forces?

Answer 44

intramolecular = forces within a molecule & are usually covalent bonds intermolecular forces = forces between molecules

Question 45

give an example of a molecule with intramolecular forces

Answer 45

water O - H bond within the molecule

Question 46

give an example of a molecule with intermolecular forces

Answer 46

water H bond between 2 water molecules

Question 47

name the types of intermolecular forces from strongest to weakest

Answer 47

H bonding permanent dipole-dipole forces induced dipole-dipole forces (AKA van der waals)

Question 48

how do induced dipole-dipole (van der waals) forces form?

Answer 48

any molecule/atom with e- can form induced dipole when it moves near an atom/molecule more e- in molecule = higher change induced dipole will form

Question 49

explain whether an induced dipole-dipole force is permanent/temporary & why

Answer 49

interaction between 2 molecules is temporary & only exists when they are nearby when they move apart, the interaction is destroyed

Question 50

state which intermolecular forces can be found in hydrocarbons & how they affect its properties

Answer 50

van der waals straight, long hydrocarbons have more van der waals = more energy needed to overcome forces - m.p increases

Question 51

explain how the arrangement of branched hydrocarbons affects its b.p

Answer 51

branched hydrocarbons can't pack together as close which weakens van der waals = lowers b.p

Question 52

what are permanent dipole-dipole interactions?

Answer 52

there are weak electrostatic forces that exist in molecules with a polarity

Question 53

what is the difference between van der waals & permanent dipole-dipole interactions?

Answer 53

permanent dipoles are stronger - have a higher m.p

Question 54

name the other type of intermolecular forces found in molecules that have permanent dipole-dipole interactions

Answer 54

van der waals

Question 55

explain how we can identify polar molecules

Answer 55

1. place a charged rod near a steady stream of a polar liquid 2. if polar molecules are present the liquid will bend towards the rod as the molecules align to face the oppositely charged rod

Question 56

when does hydrogen bonding occur?

Answer 56

between hydrogen & NOF

Question 57

name the other types of intermolecular forces found in molecules that have H bonding

Answer 57

van der waals & permanent dipole-dipole interactions

Question 58

how are H bonds shown in diagrams?

Answer 58

shown by using dotted lines

Question 59

explain why ice is less dense than water

Answer 59

ice forms a regular structure held by H bonds. & the molecules are further apart which makes it less dense than water

Question 60

explain the boiling points trend of hydrogen halides using examples

Answer 60

HF has a higher b.p than HCl as it H bonding - more energy is needed to overcome electrostatic forces there is a slight increase in b.p from HCl to HI due to the increased mass of molecule = bigger e- cloud - more van der waals