Bond valence and length

Question 1

What is Pauling’s original equation for bond length?

Answer 1

d_ij = R_ij - b * ln(v_ij)

d_ij = Bond length
R_ij = length of a single bond
b = "universal" constant, = 0.37 Å
v_ij = bond order

Question 2

What is the value of the universal constant employed in Pauling’s bond length equation?

Answer 2

0.37 Å

Question 3

In O’Keeffe & Brese’s generalisation of bond length, when will the correction factor be considerable?

Answer 3

When there is a large difference between electronegativity (e.g. CsF, where this makes up 10% of the bond length)

Question 4

Is the bond valence method suitable for metallic bonds?

Answer 4

It does accurately predict metal-metal bonds for metals with unambiguous valence (non-transition metal). But it is generally less suitable than for covalent and ionic bonds.

Question 5

What does Brown’s equal valence rule state?

Answer 5

That, subject to the bond valence constraint, bonds between like pairs of atoms have valences as nearly equal as possible.

This is equivalent to saying that the difference between A-X(1) and A-X(2) should be the same as B-X(1) and B-X(2).

Question 6

How many independent equations of bond valence do we get for a compounds with m cations and n anions?

Answer 6

m+n-1