Question

8.

7.
Calcium phosphate is found widely in nature, e.g. in bones and in the leaves of plants.
The formula for the phosphate ion is PO. Write the formula for calcium phosphate.
Boron fluoride reacts with ammonia, NH3, to make the compound shown in the
following equation.
BF3 + NH3
(i) Name the type of bond formed between N and B.
F
F
F-
F
F
F-B-N-H
(ii) Suggest a value for the F-B-F bond angle in this molecule.
Bond angle.
(iii) Explain your answer to part (ii).
F-B-N-H
H
H
H
H
[1]
[1]
[1]
[1]
******

Answer 1

The formula for calcium phosphate is Ca3(PO4)2.

(i) The type of bond formed between N and B is a coordinate covalent bond or a dative bond. This is because the lone pair of electrons on the nitrogen atom is donated to the boron atom to form a bond.

(ii) The F-B-F bond angle in this molecule is expected to be approximately 120 degrees.

(iii) This is because the molecule has a trigonal planar geometry, with the boron atom at the center and three fluorine atoms at the corners of an equilateral triangle. The lone pair of electrons on the nitrogen atom is also located in the same plane as the three fluorine atoms, and it occupies one of the corners of the trigonal planar arrangement. Therefore, the F-B-F bond angle is expected to be approximately 120 degrees, which is the ideal bond angle for a trigonal planar geometry.