Grade 9
Non-metals: chlorine, carbon, silicon
Compare molecular chlorine with network and layered forms of carbon and silicon compounds.
IntuitionNon-metals make different kinds of bonds
The sharp smell of a pool, the carbon in a pencil, and the sand in glass come from very different non-metals. Their common feature is that they usually gain or share electrons instead of forming metallic lattices.
A familiar non-metal can appear in more than one form: carbon is graphite in many pencils and diamond in gemstones, while silicon dioxide builds much of Earth’s crust.
SchoolChlorine: a reactive diatomic non-metal
Definition: Non-metal
An element whose atoms commonly form covalent molecules or anions; non-metals vary widely in state, conductivity and structure.
Chlorine is a yellow-green gas of diatomic Cl₂ molecules. It dissolves in water and reacts partly to form hydrochloric acid and hypochlorous acid.
Hypochlorous acid is a useful disinfectant because it oxidises many biological molecules. Household bleach is usually a hypochlorite solution, not dissolved chlorine gas.
| Element | Common form / property | Use or occurrence |
|---|---|---|
| Chlorine | Cl₂ gas, yellow-green | disinfection after controlled treatment |
| Carbon | graphite conducts; diamond is very hard | electrodes, pencils, cutting tools |
| Silicon | semiconductor; SiO₂ is a network solid | chips, glass, silicate minerals |
Carbon dioxide is a molecular gas used by plants in photosynthesis, while carbon monoxide is a poisonous gas made by incomplete combustion. Silicon dioxide forms an extended network, so it is a hard solid rather than a collection of separate SiO₂ molecules.
Example: How much carbon dioxide forms?
Complete combustion of 0.50 mol of carbon takes place in excess oxygen. Find the amount of CO₂.
Solution
The balanced equation has a 1:1 C:CO₂ ratio, so n(CO₂)=0.50 mol. This is about 22 g using M(CO₂)=44.0 g mol⁻¹.
UndergraduateStructure explains bulk properties
Graphite contains sheets of trigonal carbon atoms: strong covalent bonds within each sheet and weaker attractions between sheets allow sliding, while delocalised electrons conduct along the sheets. Diamond instead has a three-dimensional tetrahedral covalent network.
Silicon has four valence electrons and a diamond-like lattice. Controlled substitutional doping with group 13 or group 15 atoms creates p-type or n-type semiconductors; the device behaviour depends on carefully controlled impurities, not simply on elemental silicon alone.
Example: Distinguish the two carbon oxides
A stove burns with insufficient oxygen. Which oxide is the immediate toxic hazard, CO or CO₂?
Solution
CO is the acute poisoning hazard: it binds haemoglobin strongly and impairs oxygen transport. CO₂ at high concentration is also dangerous by displacing oxygen and causing hypercapnia, but it is not the same toxic mechanism.
References
- Chemistry of the Elements · N. N. Greenwood and A. Earnshaw, 1997