P block trends Flashcards
What are the common oxidation states of group 13 elements
+3, +1
What are the common oxidation states of group 14 elements
+4, +2
What are the common oxidation states of group 15 elements
+5, +3, -3
What is the trend of oxidation states as you go down a group and give example with group 13
- Lower oxidation states become more stable down the group
- B most stable = +3
- Tl most stable = +1
Why are elements further down the groups more stable in lower oxidation states and what groups does it apply to
- The inert pair effect
2. Group 13 and 14
What is the inert pair effect
- In forming compounds, elements in these groups promote an electron from a filled s-level state to an empty p-level.
- Increasing atomic size as you descend the group leads to weaker bonds and so a decrease in bond enthalpy- poorer overlap
- Higher promotion energies required to involve electrons in bonding
- Hence for elements at bottom of the group, the energy required to involved ns2 e- is not offset by energy gained by forming 2 new bonds.
Describe the oxidation states of group 15 elements
- Not to do with the inert paired effect
- +5 only possible with electronegative elements e.g. O,F,Cl as the high energy from formation of strong bonds offsets the promotion of energy
What is hypervalency
- Where more than 8 electrons fill the valence shell of a main group atom
- Octet rule is no longer obeyed because of MO theory
What else is important for oxidation state of group 15 and explain
- Atomic size
- PF5 is known but PI5 does not exist
- Impossible to fit 5 large iodine around p atom
- -3 is available due to increase in electronegativity as we go along the period- need a delta + metal
Where is there a large difference in properties
- Between 2nd and 3rd row
What are the differences in elements of the 2nd row
- Greater element-element bond stability
- Greater stability of multiple bonds
- Octet rule in general is obeyed
- Maximum coordination number is 4
- Lower reactivity of compounds
What is the result of greater element-element bond stability in the 2nd row
- Increased catenation- covalent bonding of 2 or more atoms of the same element to one another (single bond)
- Increased allotropy- distinct forms of an element on the same physical state- diamond and graphite
What are the results of greater stability of multiple bonds in 2nd row elements
- Double and triple bonds are more common in p2 especially (N,C, O) - use 2p orbitals which overlap effectively to form multiple bonds
- The nppi overlap diminishes with increase atomic size as they have larger more diffuse orbitals which give poorer overlap and weaker bonds
Give an example of how the octet rule is generally obeyed in 2nd row compared to 3rd row
- CF4 but not CF62-
2. SiF4 and SiF62- are both stable
Give an example of how the maximum coordination number in 2nd row is 4 compared to 3rd row
- BF3.NH3 but no BF3.2NH3
2. AlF3.2NH3 is stable
