[jsmith613]

I have two questions. Please can you help me with them

Q1)
why does Mg2+ have a greater attraction to O2- than Na+ has to Cl-.

Further, does Mg2+ have a greater attraction to O2- than Cl-.

Please explain

Q2)
Fajan's rule states that covalent character is more likley when: the positive ion has an outer electron configuration that is not a noble-gas configuration.

wiki says in explanation: Noble gas configuration of the cation produces better shielding and less polarizing power

why is this true?

[scint vile]

Mg2+ is the magnesium ion. The 2 means that two electrons have been 'lost' and the +ve sign means that the atom now carries a +ve charge. Meaning it will be attracted to a -ve charged electron(e-).
But since it is Mg2+ it has 2 +ve charges looking for 2 e-.
Now Mg2+ wants to bond with O2- because O2- is two oxygen ions 2

• - and they are both attracted to positive charges. The Mg2+ carries two +ve charges and O2- carries two -ve charges.

Na+ and Cl- are only looking for 1 e-. This is because their charge is just +. Since Mg2+ has a higher +ve charge more e- will be attracted to it.

Not sure on the second part to that question

2. A noble gas is an element with a full valance shell of e-. If the ion is in a noble-gas configuration then it will not be attracted to the opposite charge and covalent bonding will not happen.

[onenameless]

Actually, Mg2+ and Na+1 are the same molecule if you take a closer look at where they are situated in the periodic table. If Mg loses 2 electrons, it will have the same electron configuration as Neon (except for the extra 2 protons). This is also true of Na, however, the difference is that Mg has 1 more proton than Na does, so it has a more slightly positive charge. Now for O and Cl, well O2- obviously has 2 extra electrons, but Cl has only 1 extra electron so Oxygen carries a greater negative charge, and because it is situated higher on the periodic table, it's electronegative charge will be greater. So, you have a Mg ion that is more positively charged, and an oxygen that is more negatively charge so they have stronger attractions for each other.

For the second question, take the example that wiki gave you: Ca2+ is an ion whose s orbital will be empty, and you will be left with a full 3p orbital. That, compared to Hg, is not as polar because Hg2+ will lose 2 electrons in its d orbital and so 8 electrons will be left to occupy a d orbital. This lack of 2 electrons from a full d orbital, will mean that Hg is more likely to bond because it's not as stable as Ca2+ in its full p orbital. And note that Fajan's rule looks at whether something will bind covalently OR ionically, not just covalently because some atoms do not tend to form covalent bonds, depending on what the other atom is that they bind to.

[Borek]

Actually, Mg2+ and Na+1 are the same molecule if you take a closer look at where they are situated in the periodic table.

They are not the same, they are isoelectronic.

[jsmith613]

Now for O and Cl, well O2- obviously has 2 extra electrons, but Cl has only 1 extra electron so Oxygen carries a greater negative charge, and because it is situated higher on the periodic table, it's electronegative charge will be greater. So, you have a Mg ion that is more positively charged, and an oxygen that is more negatively charge so they have stronger attractions for each other.

so does this mean that Mg will have a greater attraction to O2 than F2 (even though they are in the same group) because O2 is more negative (and it should be easier to attract one, slightly larger anion that two anions)

[jsmith613]

For the second question, take the example that wiki gave you: Ca2+ is an ion whose s orbital will be empty, and you will be left with a full 3p orbital. That, compared to Hg, is not as polar because Hg2+ will lose 2 electrons in its d orbital and so 8 electrons will be left to occupy a d orbital. This lack of 2 electrons from a full d orbital, will mean that Hg is more likely to bond because it's not as stable as Ca2+ in its full p orbital. And note that Fajan's rule looks at whether something will bind covalently OR ionically, not just covalently because some atoms do not tend to form covalent bonds, depending on what the other atom is that they bind to.

But why does this produce better shielding (why does Ca2+ have better shielding than Ca+, for example)