Questions and Answers
define allotrope
different forms of the same element in the same physical state
compare the structure and bonding of CO2 and SiO2, thus account for the different phase of carbon dioxide and silicon dioxide
covalent bonding is present in both materials
different phases, CO2 being gas at normal conditions while SiO2 is a high melting point solid is due to their diff structure
CO2- covalent molecular, with strong intramolecular forces but weak intermolecular forces, it is the weak IMF that contribute to its gaseous state under room temperature
whereas SiO2 is covalent network, there are no intermolecualr forces, only intramolecular forces, which require significantly more thermal energy to break, hence the high melting and boiling point and hence it being a solid at room temeprature
diamond and graphite are two allotropes of carbon which both form a covalent network structure, both have high mp. Diamond = non-conductor of electricity and hardest known naturally occuring material. Graphite, soft and reasonable elctrical conductor. Compare and contrast these allotropes.
-bonding and structure of both -relate physical prop of hardness and electrical conductivity to particular structure
both have covalent network structure but different arrangement of atoms
diamond: 3D network of carbon atoms with every carbon atom covalently bonded to four adjacent carbon atoms, bonds are arranged in tetrahedral formation
very strong arrangement, leads to the high hardness
absence of mobile charged particles within structure ensures non-conductivity of electricity
graphite has one carbon covalently bonded to three other carbon atoms forming planar hexagonal rings of six covalently bonded carbon atoms
these planar hexagonal rings interlock with other hexagonal rings to form a 2D layer of carbon atoms
the layers are held together by weak intermolecular forces, which results in graphite being soft and slippery
each C atom shares only three of its four valence electrons, the fourth unpaired valence electron from each C atom is free to move between the 2D layers of C atoms, it is these mobile electrons which enable graphite to conduct electric current
these electrons also contribute to weak intermolecular bonding between layers of carbon atoms
