The group 1 and 2 metals Na to Cs and Ca to Ba
Do not attach these metals to the counter ions
An "amphoteric" compound will react as an acid or a base (with either a base or an acid, respectively, but generally not just water):
With acid: ZnO + 2H3O+ Zn2+ + 3H2O
With base: ZnO + 2OH- ZnO22- + H2O
The strength of the oxyacids correlates roughly with the number of =O's they have. If there are none, the acid will be very weak (e.g. HOCl). With three =O groups, the acid becomes very strong. This happens because the negative charge generated by the departure of the proton can be spread over the available (electronegative) oxygen atoms in a series of equivalent canonical structures.
In the case of the fluorosulphonic acid (e), the fluoride also boosts the acid strength since it is a strongly electron withdrawing element.
This equation can be re-written:
By the Lewis definition the B(OR)3 is the electon-pair acceptor i.e. the acid, and the hydride ion is the electron-pair donor i.e. the base.
|Note: Just because you see an "H" does not mean you are dealing with a Brønsted/Lowry acid! Remember, compounds with Na- ions are virtually unknown, but saline hydrides of the group 1 and 2 metals are well characterized.|
Hydrogen fluoride is a useful solvent. Its autoionization is:
3HF   H2F+ + HF2-
In the "general solvent system" definition of acid and bases, and acid is anything which increases the concentration of the characteristic cation of the solvent. By this definition, then, PF5 is acting as an acid. The base will be a molecule of HF.
Cl3Al:PF3 is a "classic" Lewis adduct. In the Lewis definition, AlCl3, derived from Al2Cl6, would be the electron acceptor or acid, and the PF3 is the electron donor or base.
This reaction is best classified by the Lux/Flood definition, in which an acid is an oxide ion acceptor, while a base is an oxide ion donor. SiO2 will be the acid, and Na2O the base.
ClF3 is a liquid capable of some autoionization:
2ClF3   ClF2+ + ClF4-
Since NOF results in an increase in the ClF4- concentration it would be classified in the general solvent system definition as a base.
In the Lewis definition, NOF is acting as a source of F-, an base because it has 4 lone-pairs of electrons. The ClF3 acts as an electron acceptor, i.e. the acid.
|A few students, evidently anxious to make sure all the options were covered, invoked the Bronsted/Lowry definition on reactions where there was no hydrogen at all. Think!|
The molecules involved in biological systems have several characteristics relevant to this question. They are large and complex, featuring long and often unsaturated chains. They are also relatively stable to decomposition, notably by water.
Carbon readily forms double and triple bonds with itself and the other non-metallic atoms of the first short period which allows for an effectively unlimited number of different molecules. Because its normal valence is limited to four i.e. it cannot form more than four 2-centre, 2-electron bonds, its compounds can be relatively stable to attack.
Silicon has limited ability to form chains of Si atoms singly bonded to each other because the Si-Si bond is relatively weak, and it does not form multiple bonds to itself or other atoms under normal circumstances because of poor p-bonding overlap. On the other hand, it has a great affinity for oxygen, as displayed by the great variety of robust silicates, and silicones known.
In addition many silicon compounds are susceptible to chemical attack through 5 and 6-coordinated intermediates (see part (b)) which limits the chemical stability of many of its compounds.
The overall reaction of SiCl4 would produce silicic acid Si(OH)4 via a series of steps involving 5 or 6-coordinated silicon. These higher coordination numbers are available if silicon uses its empty d-orbitals to form sp3d or sp3d2 hybrid orbitals. They are not available to carbon which has no additional low-lying orbitals to use.
(The reaction would not really yield pure silicic acid because Si-O-Si links rapidly form by loss of water:
(HO)3Si-O-H + H-O-Si(OH)3 (HO)3Si-O-Si(OH)3 + H2O etc
The result is a gel containing very ill-defined compounds.)
For the p-block elements, the electron configuration is [core]ns2npx, where x = 1 to 6. The inert pair effect refers to a tendency, which increases down a group, for the 2 electrons in the ns orbitals not to be involved in bonding. This arises because, the promotion energy needed to form hybrids is not compensated for by the energy recovered by the extra bond formation, and also because the gap between the ns and np subshells gradually increases due to the effect of the increasing number of electrons in the core. Recall that in a one-electron system e.g. hydrogen, the subshells of the same n, but different l, have the same energy, but for multi electron atoms, differential penetration into the core by s, p and d electrons leads to the observed energy differences.
Group 14 includes C, Si, Ge, Sn and Pb. Carbon is tetravalent in virtually all its stable compounds, but as we go down the group, the divalent state, characterised by primarily ionic M2+ compounds, becomes more and more important. At lead, the tetravalent state is rare. The following reactions illustrate this:
GeCl2 + Cl2 GeCl4 Very rapid at 25 oC.
SnCl2 + Cl2 SnCl4 Slow at 25 oC.
PbCl2 + Cl2 PbCl4 Requires heat and/or pressure.
The ground state configuration of the group 17 elements (F, Cl, Br, I) is [core]ns2np5nd0. In this configuration oxidation states of I or -I are possible. Examples are HF, ClF and Br-.
The possible excited states, for all except fluorine, are:
ns2np4nd1 leading to the III state, for example ClF3 and IF4-
ns2np3nd2 leading to the V state, for example BrF5 and IF6-
ns1np3nd3 leading to the VII state, for example IF7
The range of compounds is limited by steric effects.