Molecular shapes and orbitals

Question 1

chemical bond

Answer 1

link between 2 atoms

forms if resulting arrangement of the nuclei and their e- has lower energy than total energy of separate atoms (i.e. more energetically favourable)

Question 2

name of group 6 elements

Answer 2

chalcogens

Question 3

types of bonding

Answer 3

1. ionic
2. covalent
3. metallic

Question 4

types of bonding models

Answer 4

1. valence bond theory (localised)
2. molecular orbital theory (delocalised)

Question 5

why does hypervalence exist?

Answer 5

due to free d-orbitals

Question 6

dative bond

Answer 6

one atom donating a lone pair of e- in one orbital into a vacant orbital on another atom

Question 7

resonance

Answer 7

e- in molecules aren’t always localised to specific bonds

Lewis structure preducts 1 double bond and 2 single bonds (actually both lengths are equal + charges = shared)

used to explain that actual structure is a hybrid of all possible forms

charge = delocalised

Question 8

which position would double bonds occupy - axial or equatorial?

Answer 8

equatorial - minimises space and repulsion

Question 9

which occupy more space - electronegative sub. or electropositive sub.?

Answer 9

bonded pairs to electropositive substituents

Question 10

stereochemically inactive lone pair

Answer 10

occurs if l.p. is in an s-orbital and is evenly distributed around the molecule (∴ has no impact on shape)

Question 11

possible structures with 5 valence e-

Answer 11

1. trigonal bipyramidal - more likely
2. square based pyramid

Question 12

fluxional

Answer 12

isomers that can undergo dynamic interchanges between atoms in symmetry-equivalent positions

Question 13

which position do lone pairs always occupy?

Answer 13

equatorial

Question 14

Berry pseudorotation

Answer 14

the process which scrambles axial and equatorial ligands on a trigonal bipyramidal

Question 15

how to prevent flux between molecules?

Answer 15

reaction @ low temp. (freeze it out)

product = only thermodynamic one (might not be most kinetically stable one)

Question 16

VSEPR - single/multiple bonds

Answer 16

indistinguishable

multiple bond treated as single bond of higher e- density

Question 17

electronegativity + effect of bond polarity on BP/LP in orbital arrangements

Answer 17

more polar bonds concentrate e- density at one atom or the other

also influence e- repulsion

e.g. e- density closer to F than Cl (more electronegative) - make it easier to push bonding pairs together to maximise BP-LP repulsion

Question 18

order of repulsion power

Answer 18

LP-LP (strongest)

LP - double bond

LP - single bond

double bond-double bond

double bond-single bond

single bond-single bond (weakest)

Question 19

rotation by 180°

Answer 19

C2 rotation

Question 20

rotation by 120°

Answer 20

C3 rotation

Question 21

rotation by 60°

Answer 21

C4 rotation

Question 22

rotation by 90°

Answer 22

C6 rotation

Question 23

transition metal

Answer 23

metal in an element in which the valence e- = d electrons

Question 24

“d-block” or “transitional”

Answer 24

elements with partially full or full d-shells

Question 25

Haemoglobin

Answer 25

O2 transport contains dicationic Fe2+ metal centre surrounded by nitrogen-based ligand (= haem ligand) complex binds via l.p. on oxygen to form saturated coordination Fe2+ complex CO and CN- are good ligands for Hb and compete for Fe2+ site (∴ toxic)

Question 26

ligand

Answer 26

group or atom that gives metal centre pair of e-, normally available via l.p. metal ion = Lewis acid (acceptor) ligand = Lewis base (donator)

Question 27

monodentate ligand

Answer 27

only binds to metal through 1 l.p. of electrons

Question 28

polydentate ligand

Answer 28

binds to metal via 2 or more lone pairs

Question 29

shape of transition metals

Answer 29

d-block elements have 9 orbitals available - VSEPR doesn't work shape dictated by no. of coordinated atoms around metal

Question 30

chiral molecules

Answer 30

non-superimposable mirror images (related by enantiomers)

Question 31

coordination isomers

Answer 31

ligands attached to each of the 2 metals are different

Question 32

linkage isomers

Answer 32

involve ambidentate ligands M-NCS or M-SCN

Question 33

polymerisation isomers

Answer 33

same forumla, different molar mass (same empirical formula)

Question 34

stability constant and hard/soft acids + bases

Answer 34

if Kf is large = ligand binds more tightly to metal centre than H2O if Kf is small = ligand binds less tightly to metal centre than H2O

Question 35

chelate effect

Answer 35

complex containing one or more 5/6 membered chelate rings is more stable (stability constant = larger) than one without chelate ring due to thermodynamics choose polydentate ligand over monodentate larger log(β) value

Question 36

chelate effect + ring size

Answer 36

decreases as ring size increases chance of "dangling arm" binding to metal becomes smaller 4 membered ring = 5-membered ring > 6-membered ring > 7-membered ring

Question 37

early transition metals (Ti, V, Cr) + halides

Answer 37

complexing strength = F- >> Cl- > Br- > I-

Question 38

later transition metals + halides

Answer 38

complexing strength = I- >> Br- > Cl- > F-

Question 39

hard cations

Answer 39

high density charge less polarisable form more stable complexes with hard ligands

Question 40

soft cations

Answer 40

low density charge more polarisable form more stable complexes with soft ligands

Question 41

hard acids

Answer 41

prefer to complex with hard bases

Question 42

soft acids

Answer 42

prefer to complex with soft bases

Question 43

do hard-hard or soft-soft interactions have greater electrostatic/ionic contribution?

Answer 43

hard-hard

Question 44

do hard-hard or soft-soft interactions have greater orbital/covalent interactions (overlap)?

Answer 44

soft-soft

Question 45

trend in hardness down a group

Answer 45

decreases orbitals get larger + more diffuse electronegativity decreases

Question 46

influence of electronegativity on hardness/softness of an element

Answer 46

more electronegative = harder (less polarisable)

Question 47

influence of size on hardness/softness of an element

Answer 47

smaller element/ion = harder