General group 13, 14 and 15. Flashcards
What are the oxidation states of group 13?
+1 and +3.
What are the oxidation states of group 14?
+2 and +4.
What are the oxidation states of group 15?
+5, +3 and -3.
What is the trend in oxidation state down group 13 and what is this called?
A lower oxidation state becomes more stable down the group - this is due to the inert pair effect.
What causes the inert pair effect?
The increasing atomic size down the group makes weaker bonds (due to decreased bond energy) and there are higher promotion energies required to involve electrons in bonding - for elements at the bottom of the group the energy required to involve the ns2 electrons is not offset by the energy gain when the two new bonds are formed.
In group 15, for which elements is the +5 oxidation state possible for?
When bonded to electronegative elements such as O, F and Cl as the high energy from the formation of the strong bonds offsets the promotion energy. It can be thought of as a simple sp3d hybridisation, but MO theory where atoms form molecules provides a better explanation.
What are the differences between the properties of 2nd and 3rd row elements?
The 2nd row has greater element-element bond stability and greater stability of multiple bonds (pi bonds), the octet rule is obeyed (generally), the maximum coordination of the 2nd row is 4 and there is lower reactivity of compounds.
Why is there greater element-element bond stability in the second row than the third row?
There is increased catenation - the covalent bonding of two or more atoms of the same element to one another and increased allotropy - the distinct forms of an element in the same physical state such as graphite, diamond, C60.
Why is there greater stability of multiple bonds in the 2nd row than the 3rd row?
There are larger more diffuse orbitals with increasing atomic size resulting in weaker bonds. Double and triple bonds are more common especially in C, N and O using p orbitals which overlap effectively.
What is an example of which the octet rule of obeyed in row 2 but not row 3?
CF4 is stable whereas CF62- is not, and SiF4 and SiF62- are both stable.
What is an example of how the maximum coordination number of row 2 is 4 whereas it’s not in row 3?
BF3 . NH3 is stable whereas BF3 . 2NH3 is not, whereas AlF3 . 2NH3 is known and stable.
What are the reasons for the differing properties between row 2 and 3?
2nd row elements are especially small, they have a high electronegativity (so strong bonding), the access to low lying antibondinging MOs along with the small size limits the oxidation number and coordination number.
