Final answer:
Electrons within a metallic lattice do not screen each other effectively due to their delocalized nature within the metallic bond, where a 'sea' of mobile valence electrons surrounds the metal ions.
Step-by-step explanation:
Electrons within a metallic lattice do not screen each other very well. This is because in a metallic bond, which is characteristic of a metallic lattice, the electrons are delocalized. This means that they are free to move throughout the lattice and are not bound to any specific atom. Unlike ionic or covalent bonds where electrons are more localized, in a metallic bond, the sea of electrons surrounding the metal cations are capable of moving through the entire crystal, reducing their ability to screen each other from the nuclear charge of the ions effectively.
Contrary to this, in an ionic crystal, ions are held in place by the electrostatic forces in the crystal lattice, making it harder for electrons to be free and mobile. In a covalent bond, electrons are shared between atoms and are localized in shared orbitals. This result differs from the metallic crystal where the unique structure of the lattice causes lesser electron screening.