what will the oxidation number do?

Question

An atom has an oxidation number if -3 in a molecule. it is placed in another molecule whose other atoms are significantly less electronegative than the atoms in the first molecule.

Answer 1

Can you be a little more specific about your question? Like give an example or a specific problem.

If an atom has an oxidation number of 3-, that essentially means it has gained 3 e-. Most of the time, this means it is in an ionic bond with an atom(s) with much lower electronegativities. Like K₃P, or FeN, or Mg₃N₂, where K⁺ needs 3 K's to balance the 1 atom of P^3- (3 x 1+ = 3+ & 1 x 3- = 3-, to sum to 0), or Fe³⁺ needs 1 atom to balance the N^3- (3+ = 3- to sum to 0), and need 3 Mg²⁺ to balance the 2 N^3- (3 x 2+ = 6+ & 2 x 3- = 6-, to sum to 0).

So, moving the 3- atom (most likely from the Nitrogen family, or the Boron atom) to a molecule with less electronegativity will not have any effect on the oxidation. This 3- atom will not participate in a redox reaction, it will be a spectator ion. Now, if you are talking formal charge instead of oxidation state, again, it will not participate as it will go from 3- to 3-, meaning it is not oxidized or reduced. But, a 3- formal charge is not limited to only the Nitrogen family, some other elements (typically nonmetals) can also have a formal charge of 3- depending on the redox reaction. For REDOX, Oxygen almost always forms 2-, and H is generally 1+. The rest follow their trends from the periodic chart.

NOTE: 1A metals are 1+, 2A metals are 2+, Transition metals are typically 2+, but can be up to 6+, depending on the element & where on the chart it is, Boron Group metals (mostly excludes B, which is usually 3-) are 3+, Carbon family nonmetals are 4- (metals are 4+ like Sn, or Pb), Nitrogen Group nonmetals are 3-, Oxygen Group nonmetals are 2-, Halogens are 1-, and Noble Gases are 0. Elements in their natural state DO NOT have an Oxidation number, so = 0. This means that the diatomic (H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂, At₂) have an oxidation state of 0, but H¹⁺, N^3-, O^2-, F^-, Cl^-, Br^-, I^-, At^- after undergoing redox. All metals are 0, BEFORE losing e-, and then they go to cations (positive ions). H can also form H^- when acting as a hydride of a metal.

However, if you had N₂ + 6e- ---> 2N^3-, then the N has gone from oxidation state of 0 to that of 3-, which would be a change in oxidation state because each N gained 3 e-. This would be a reduction. If you had Fe --> Fe³⁺ + 3e-, this would be an oxidation, since the iron lost 3 e-.

The mnemonic to remember is LEO goes GER. Lose Electrons OXIDIZED, Gain Electrons REDUCED or OIL RIG, oxidation involves loss, reduction involves gain. The element that is oxidized (lose e-) is the reducing agent (brings about the reduction) and the element that is reduced (gain e-) is the oxidizing agent (brings about the oxidation).

Electronegativity determines how likely the atom is to gain, lose, or partially share the e-. Electronegativities below 2.0 are typically metals, with the 1A metals having the lowest values and they tend to lose e- (get oxidized). Electronegativities above 2.0 are typically nonmetals, with O having a 3.5, F having the highest at 4.0, and the nonmetals tending to gain e- (get reduced). An electronegativity difference will tell the "type" of bond between the atoms: 0 to 1.0 non polar covalent (equal sharing), 1.0 to 1.5 polar covalent (unequal sharing with the e- closer to the more electronegative atom), and > 1.5 ionic (complete transfer of e- from metal to nonmetal).

If you add in symmetry of the molecule, you can determine the polarity of the molecule. Ionic bonds always produce asymmetry ==> polar compound (will dissolve in water). Polar covalent bond and Asymmetry ==> polar molecule (will dissolve in water, which is polar). Non-polar covalent bond OR Symmetry ==> non-polar molecule (will dissolve in oil, not water, oil is non polar). Like dissolves like. This means a polar compound will dissociate into the ions surrounded by water as: + ion by 6 water molecules with the O side closer to the ion, and - ion by 6 water molecules with H side closer to the ion. Strong acids (HNO₃, H₂SO₄, HCl, HBr, HI, HClO₄) will completely dissociate (break apart) in water into H⁺ and X^-. Strong bases (NaOH, KOH, Mg(OH)₂, Ca(OH)₂) will completely dissociate in water into Y⁺ and OH^-. All other acids and bases will only partially dissociate. Most ionic salts completely dissociate in water into cations and anions.