P-Block

Question 1

What is ionisation energy?

Answer 1

an always positive energy required to remove an electron from atom in its ground state

Question 2

Name generic trends in ionisation energy

Answer 2

increases from left to right along periods and decreases down groups

Question 3

What does the value of IE depend on

Answer 3

distance between nucleus and the electron

Question 4

Why is there often deviations with trends of IE

Answer 4

if new shells are used or symmetry can be restored

Question 5

Why do Ga and Ti have higher IE?

Answer 5

as D-Orbitals are occupied so more shielding is present

Question 6

What is electron affinity?

Answer 6

Energy released when an atom/ion gains an electron

Question 7

What are the general trends with electron affinity

Answer 7

increases from left to right along periods due to higher nuclear charge and decreases down groups due to shells being further away from nucleus

Question 8

What is Slaters rule

Answer 8

outermost electrons feel a less nuclear charge than the actual nuclear charge due to shielding effects from inner electrons

Question 9

What happens t the radius of atoms from left to right and why

Answer 9

radius contracts due to the increase of nuclear charge

Question 10

What happens to the radius of atoms down groups

Answer 10

radius increases as number of shells increases

Question 11

Why are P-electrons higher in energy?

Answer 11

they penetrate the nuceus less than the s orbitals so p-orbitals are less stabilised

Question 12

What is the inert pair effect

Answer 12

tendency of electrons in outermost atomic s-orbital to remain unshared in compounds

Question 13

What happens to bond strengths down a group?

Answer 13

Bonds become weaker and longer as the valence orbitals are larger and so less electron dense so less overlap

Question 14

Why do only first row elements form multiple bonds

Answer 14

the 2p pi orbitals are small and electron dense so give good overlap

Question 15

Why is the B-F bond so strong

Answer 15

small, electron dense orbitals so very effective overlap forming a polar covalent bond

Question 16

What is the general trend for bond energy of hydrides

Answer 16

bond energies increase from left to right due to no lone pairs on H and greatest electronegativity on RHS

Question 17

What is a triel bond

Answer 17

bond between a group 13 element and a halide, which act as Lewis acids

Question 18

What shape is the molecule BF3

Answer 18

trigonal planar due to its sp2 hybridisation

Question 19

Why is BF3 a stronger Lewis acid than BI3

Answer 19

because iodine has larger more diffuse orbitals so less efficient overlap

Question 20

give 2 examples of hydride reducing agents

Answer 20

LiAlH4 and NaBH4

Question 21

What are Wades rules used for?

Answer 21

used to explain structures of boron hydrides and work out number of pairs of electrons for bonding

Question 22

roughly explain wades rules

Answer 22

each BH unit donates 2 electrons, any extra hydrogens also donate one electron each, negative charge means an extra electron, number of pairs -1 means number of vertices in structure

Question 23

what is a carborane?

Answer 23

where 1 or more B atoms is replaced with a Carbon atom. wades rules can also be used for carboranes

Question 24

what are allotropes

Answer 24

different structural forms of the same element

Question 25

what are the general trends in oxidation state down group 14

Answer 25

+4 OS is most common at the top of the group but as you go down the gorup +2 is more stable due to the inert pair effect

Question 26

what happens to the stability of the hydrides as you go down the group 14

Answer 26

stability decreases down group 14 due to increasing bond lengths

Question 27

whats the difference between carbon halides and other group 14 halides

Answer 27

CX4 is hydrolytically stable but all the others are volatile and susceptible for nucleophilic attack as X is a good leaving group, bond strengths increase down the group as an increasing electronegativity difference

Question 28

how can halides form silanes

Answer 28

halide + alcohol = silane

Question 29

how are silicones formed?

Answer 29

hydrolysis of silylhalides to form silanol, then condensation of silanol to form siloxane. different monomer units are needed for terminal, chain and cross linking units.

Question 30

why is the Si-O bond so strong?

Answer 30

P-pi D-pi bonding. the filled 2p orbital of O donates into empty 3d orbital of Si. the bond is so strong it only reacts with fluorinating agents

Question 31

give an example of an organosilane and its properties

Answer 31

TMS, which is the reference for NMR, stable due to shielding and not polar bonds.

Question 32

why cant low period elements easily make triple and double bonds, how can you make them form pi bonds?

Answer 32

sigma bonds are preferred to pi bonds, but by using bulky sterically hindering groups can block oligomerisation to stop metal centres form polymerising via sigma bonds

Question 33

Why are lower valence compounds favoured by lead

Answer 33

the inert pair effect meaning and the relativistic effect

Question 34

explain the general trends in ionisation energy group 15

Answer 34

Ionisation energy decreases due to the increase in distance from electron to nucleus

Question 35

what range of oxidation states does group 15 have?

Answer 35

varies from -3 to +5

Question 36

why is the P=O bond so strong

Answer 36

P-pi D-pi bonding by donation of p electrons of O into Dorbital of P, often a driving force for mamy reactions. explains why some phosphorus is very reactive with oxygen

Question 37

What is P-pi D-pi bonding

Answer 37

when electron density from a p-orbital donated into another atoms d-orbital to form very strong covalent bonds

Question 38

What oxidation states is phosphorus in phosphorus oxides

Answer 38

Phosphorus 5 or phosphorus 3

Question 39

Describe the nitrite ion

Answer 39

NO2- ion, the nitrogen is 3+ oxidation state, trig planar shape

Question 40

Describe the nitronium ion

Answer 40

NO2+ ion, Nitrogen in 5+ oxidation state, linear shape

Question 41

what is the general trend with hydride bonding down group 15

Answer 41

bond energy decreases down group, so does the bond angle, due to valence electrons being further away from nucleus

Question 42

why does NH3 have a relatively high BP for group 13 hydrides

Answer 42

has high polarity and strong H bonding, is basic

Question 43

what makes phosphorus a good ligand

Answer 43

can be used as PR3 which takes a cone angle shape which accepts electrons from metal orbitals

Question 44

What are the two halide formations for group 15 elements

Answer 44

MX3 or MX5 but only MX5 can be formed with smaller halides due to strong bonds needed

Question 45

Describe properties of PF3

Answer 45

gas at room temp, similar ligand to CO as the electronegativity of F lowers energy of the P 3d orbitals giving good pi backbonding

Question 46

how do you find pKa

Answer 46

pKa = -log Ka

Question 47

what does a small pKa mean

Answer 47

small pKa = large Ka = strong acid

Question 48

What are Dragos rules used for? what are they?

Answer 48

if Dragos rules are true, no need to consider hybridisation for the central atom (pure p-orbital bonding) -if central atom has at least 1 lone pair -if central atom belongs to group 13,14,15,16 between 3-7 period -if electronegativity of surrounding elements in 2.5 or less -if sum of sigma bonds + lone pairs =4

Question 49

What are wades rules used for? what are they?

Answer 49

predicting the structure of boranes/carboranes cluster bonding each BH/CH unit donates 2 electrons, each bridging H atom donates 1 e, negative charge adds 1 e, if we have n pairs then polyhedron formed has n-1 vertices. compare number of vertices to number of non H atoms and see if your short. closo, nido or arachno