Question

What is the nature of the P-O bond in phosphorus pentoxide (P2O5)?

Answer 1

When you talk about the 'nature' of the bond, I presume you're referring to whether the bond is ionic, polar covalent, purely covalent an so on. Generally, we will need an electronegativity table to help us with this. This is essentially just a periodic table but with the electronegativity values of atoms of each element written beside them instead.

If we want to determine the nature of the P-O bond in P2O5, then we have to look up the electronegativity values of P (Phosphorus) and O (Oxygen). The electronegativity of an atom is the relative attraction that atom has for the shared pair of electrons in a covalent bond (i.e. The higher the electronegativity, the greater the attraction). We then subtract the two electronegativity values from each other (i.e. largest value - smallest value) and we will be left with an answer. As a general rule of thumb, we say that:

-Values in the region of 0-0.5 will by purely/strongly covalent in the bond they form. Each atom forming the bond has a similar attraction for the shared electrons, and so will cancel each other out. In this way, the electrons end up being reasonably equally shared, sitting in between the two atoms.
-Values in the region of 0.5-1.6 are most likely related to a polar covalent bond. This means that while electrons are shared between the two atoms, they are not evenly so. One atom has a significatly greater attraction for them then the other, leading to the pair of electrons sitting closer to this atom in the bond and a polar bond being formed.
- Values between 1.6 and 2.0 are considered to relate to the formation of an ionic bond between the two atoms, other than if these two atoms are both non-metals, in which case it is considered to be a polar covalent bond.
-Values greater than 2.0 generally mean that the electrons are completely transferred from one atom to another, leading to two oppositely charged ions being formed and an ionic bond between any two atoms.

http://www.chemteam.info/Bonding/Electroneg-Bond-Polarity.html

The electronegativity values for P and O are:
P = 2.1
O = 3.5

So, if we take the largest from the smallest, we get:
3.5 - 2.1 = 1.4

So, based on what we said above, you should be able to work out what type of bond is formed between the phosphorus and oxygen atoms. Hope that helps!