Covalent bonding
Group IV atoms Group IV atoms do not lose or gain electrons in order to obtain the octet structure. They prefer to share electrons with other atoms to form molecules. The electrostatic attraction force between shared electrons and positive nuclei is called covalent bond.
Molecules C H x Methane CH4 Tetrachloromethane, CCl4 C Cl x
Molecules Si H x Silane SiH4 Silicon tetrachloride, SiCl4 Si Cl x
Molecules Hydrogen H2 Chlorine, Cl2 Fluorine, F2 Single bond H + x H Bond pair Hydrogen H2 Chlorine, Cl2 Fluorine, F2 x x x x x x Cl x + Cl x Cl Cl x x x x x x Single bond + x F
Molecules Oxygen, O2 Nitrogen N2 Hydrogen chloride, HCl Double bond + x O Oxygen, O2 Nitrogen N2 Hydrogen chloride, HCl Double bond + x N Triple bond + x H Cl
Molecules Ammonia NH3 Phosphorus trichloride, PCl3 Lone pair H N P Cl x Lone pair Ammonia NH3 Phosphorus trichloride, PCl3 P x Cl
Molecules H O x Lone pair Water, H2O Carbon dioxide CO2 x O C
Molecular formulae
Molecular formulae
Molecules Molecules are formed from non-metal elements. There are strong covalent bonds within molecules. However, only weak van der Waals’ forces between molecules.
Simple molecular structure Water, ammonia, dry ice (solid carbon dioxide) o = c = o Weak van der Waals’ forces
Simple molecular structure Iodine Iodine molecule
Properties of simple molecular compounds They are usually liquids (water) and gases (oxygen). Only a few is solids (iodine and dry ice). The solids are relatively soft. Low melting points and boiling points. Usually they are insoluble in water, but soluble in 1,1,1-trichloroethane. They are electrical non-conductors (without mobile ions).
Reasons They have simple molecular structures with weak van der Waals’ forces between molecules.
Carbon atom Carbon atom do not lose or gain electrons in order to obtain the octet structure. It prefers to share electrons with other atoms to form molecules. How about in pure carbon? How do carbon atoms combine together?
Carbon atom Each carbon atom has 4 outermost shell electrons, they tend to gain 4 extra electrons to obtain octet structure. As a result, each carbon atom forms covalent bonds with 4 other carbon atoms. C x C x extend infinitely
Diamond Diamond has a giant covalent structure with of a network of strong covalent bonds. Each carbon atom is covalently bonded to 4 other carbon atoms. Similar for silicon. Carbon atoms Covalent bonds
Graphite Graphite is another form of carbon. It has very high melting point and boiling point. It conducts electricity and so it is used as electrode.
silicon oxygen Quartz, SiO2 Silicon and carbon are group IV elements, so they are similar in structure. When silicon combine with oxygen, each silicon atom is covalently bonded to 4 oxygen atoms. While each oxygen atom is covalently bonded to 2 silicon atoms. Therefore, the formula is SiO2.
Giant covalent structure Diamond and quartz are both giant covalent compounds. Their melting points (diamond: ~3500C) and boiling points are very high. They are very hard and insoluble in water. They are electrical insulator (except graphite). They have giant covalent structure with a network of strong covalent bonds between atoms.