Final answer:
Carbon, a non-metallic element, forms the graphite in pencils with a structure that consists of layers of carbon atoms in a trigonal planar arrangement, making it soft, slippery, and electrically conductive.
Step-by-step explanation:
The graphite in a pencil is composed of carbon, which is a non-metallic element. Carbon is able to form a variety of allotropes, including graphite and diamond, due to its capability to create different types of bonds and structures. Specifically, graphite is composed of layers of carbon atoms that are bonded covalently in a trigonal planar arrangement with sp²-hybrid orbitals. These layers are not bonded strongly in the vertical direction, which is why graphite is soft and slippery, allowing it to leave marks on paper. The structure also grants it the ability to conduct electricity, as the unhybridized p orbitals can form π bonds allowing electrons to move more freely within layers.