In urea, each nitrogen atom uses three of its valence electrons for formation of single bonds with carbon atom and two hydrogen atoms.
Ionic solids—Made up of positive and negative ions and held together by electrostatic attractions. They're characterized by very high melting points and brittleness and are poor conductors in the solid state. An example of an ionic solid is table salt, NaCl.
A substance has a definite shape when it is a solid, that way it can hold its shape.
