Chemical properties of the halogens
atomThe smallest part of an element that can exist. of group 7The vertical column of non-metal elements next to group 0 in the periodic table, also called the halogens. elementA substance made of one type of atom only. all have seven electronSubatomic particle, with a negative charge and a negligible mass relative to protons and neutrons. in their outer shell. This means that the halogenAn element placed in group 7 of the periodic table, which starts with fluorine and ends with astatine. The name 'halogen' means 'salt-producing' because halogens produce a range of salts when they react with metals. all have similar chemical propertiesA description of how a substance reacts with other substances. For example, flammability, pH, reaction with acid, etc..
Reactions with metals
The halogens react with metals to produce saltThe substance formed when the hydrogen ion in an acid is replaced by a metal ion. (the word 'halogen' means 'salt former'). For example, chlorine reacts with sodium:
Sodium + chlorine 鈫 sodium chloride
2Na(s) + Cl2(g) 鈫 2NaCl(s)
Sodium and chlorine react vigorously when heated, giving an orange flame and clouds of white sodium chloride.
The halogens become less reactiveThe tendency of a substance to undergo a chemical reaction. going down group 7. The table describes what is seen when halogens react with iron wool.
| Halogen | Reaction |
| Fluorine | Cold iron wool burns to produce white iron(III) fluoride |
| Chlorine | Hot iron wool burns vigorously to produce orange-brown iron(III) chloride |
| Bromine | Hot iron wool burns quickly to produce red-brown iron(III) bromide |
| Iodine | Hot iron wool reacts slowly in iodine vapour to produce grey iron(II) iodide |
| Halogen | Fluorine |
|---|---|
| Reaction | Cold iron wool burns to produce white iron(III) fluoride |
| Halogen | Chlorine |
|---|---|
| Reaction | Hot iron wool burns vigorously to produce orange-brown iron(III) chloride |
| Halogen | Bromine |
|---|---|
| Reaction | Hot iron wool burns quickly to produce red-brown iron(III) bromide |
| Halogen | Iodine |
|---|---|
| Reaction | Hot iron wool reacts slowly in iodine vapour to produce grey iron(II) iodide |
Question
Write a balanced equation for the reaction of iron with chlorine to produce solid iron(III) chloride, FeCl3. Include state symbols.
2Fe(s) + 3Cl2(g) 鈫 2FeCl3(s)
Reactions with hydrogen
The halogens react with hydrogen to produce compoundA substance formed by the chemical union of two or more elements. called hydrogen halides. For example, chlorine reacts with hydrogen:
Hydrogen + chlorine 鈫 hydrogen chloride
H2(g) + Cl2(g) 鈫 2HCl(g)
The hydrogen halides are gases at room temperature. They dissolveWhen a substance breaks up and mixes completely with a solvent to produce a solution. in water to produce acidicHaving a pH lower than 7. solutionMixture formed by a solute and a solvent.. Hydrogen chloride dissolves in water to produce hydrochloric acid, HCl(aq).
The table describes what is seen when halogens react with hydrogen.
| Halogen | Reaction |
| Fluorine | Explodes in the cold and dark, forming hydrogen fluoride |
| Chlorine | Explodes with a flame or in sunlight, forming hydrogen chloride |
| Bromine | Vigorous reaction with burning hydrogen, forming hydrogen bromide |
| Iodine | Very slow reaction when heated strongly, forming some hydrogen iodide |
| Halogen | Fluorine |
|---|---|
| Reaction | Explodes in the cold and dark, forming hydrogen fluoride |
| Halogen | Chlorine |
|---|---|
| Reaction | Explodes with a flame or in sunlight, forming hydrogen chloride |
| Halogen | Bromine |
|---|---|
| Reaction | Vigorous reaction with burning hydrogen, forming hydrogen bromide |
| Halogen | Iodine |
|---|---|
| Reaction | Very slow reaction when heated strongly, forming some hydrogen iodide |
Example
Astatine is placed below iodine in group 7. Use the information to predict the reaction of astatine with hydrogen.
Astatine should react very slowly with hydrogen, even when heated. A little hydrogen astatide should form, which should dissolve in water to form an acidic solution.
Chemical test for chlorine
Damp litmus paperA type of indicator that can be red or blue. Red litmus turns blue in alkalis, while blue litmus turns red in acids. is bleached white when it is placed in chlorine. If damp blue litmus paper is used, the paper turns red then white.