Pencil Pencil A pencil is an implement for writing or drawing constructed of a narrow, solid pigment core inside a protective casing which prevents the core from being broken and/or from leaving marks on the user’s hand during use. Pencils create marks by physical abrasion, leaving behind a trail of solid core material that adheres to a sheet of paper or other surface. They are distinct from pens, which instead dispense liquid or gel ink onto the surface being marked. Most pencil cores are made of graphite powder mixed with a clay binder. Graphite pencils (traditionally known as 'lead pencils') are
Lead of lead exceeds that of tin, contrary to what periodic trends would predict. Relativistic effects, which become significant in heavier atoms, contribute to this behavior. One such effect is the inert pair effect: the 6s electrons of lead become reluctant to participate in bonding, making the distance between nearest atoms in crystalline lead unusually long. Lead's lighter carbon group congeners form stable or metastable allotropes with the tetrahedrally coordinated and covalently bonded diamond cubic structure. The energy levels of their outer s- and p-orbitals are close enough to allow mixing into four hybrid sp orbitals. In lead, the inert pair