Chemistry · Ch 7 — The p-Block Elements
Occurrence
7.18.1
Occurrence
Where the Halogens Are Found
Fluorine and chlorine occur fairly abundantly in nature, while bromine and iodine are comparatively scarce.
- Fluorine is locked up mainly in insoluble fluoride minerals — fluorspar (), cryolite () and fluoroapatite () — with only trace amounts turning up in soil, river water, plants, and the bones and teeth of animals.
- Seawater carries dissolved sodium, potassium, magnesium and calcium salts (their chlorides, bromides and iodides all present), but is overwhelmingly a sodium chloride solution (about 2.5% by mass). Where ancient seas have dried up, their salt deposits — sodium chloride and carnallite, — remain behind.
- Iodine finds its way into certain marine organisms: seaweeds can concentrate up to 0.5% iodine, and Chile saltpetre carries up to 0.2% sodium iodate.
The atomic and physical properties of the Group 17 elements (excluding tennessine) are collected below, along with their electronic configurations.
| Property | F | Cl | Br | I | At |
|---|---|---|---|---|---|
| Atomic number | 9 | 17 | 35 | 53 | 85 |
| Atomic mass/g mol⁻¹ | 19.00 | 35.45 | 79.90 | 126.90 | 210 |
| Electronic configuration | [He]2s²2p⁵ | [Ne]3s²3p⁵ | [Ar]3d¹⁰4s²4p⁵ | [Kr]4d¹⁰5s²5p⁵ | [Xe]4f¹⁴5d¹⁰6s²6p⁵ |
| Covalent radius/pm | 64 | 99 | 114 | 133 | – |
| Ionic radius X⁻/pm | 133 | 184 | 196 | 220 | – |
| Ionisation enthalpy/kJ mol⁻¹ | 1680 | 1256 | 1142 | 1008 | – |
| Electron gain enthalpy/kJ mol⁻¹ | –333 | –349 | –325 | –296 | – |
| Electronegativity (Pauling) | 4.0 | 3.2 | 3.0 | 2.7 | 2.2 |
| ΔhydH(X⁻)/kJ mol⁻¹ | 515 | 381 | 347 | 305 | – |
| Melting point/K (of X₂) | 54.4 | 172.0 | 265.8 | 386.6 | – |
| Boiling point/K (of X₂) | 84.9 | 239.0 | 332.5 | 458.2 | – |
| Density/g cm⁻³ | 1.5 (liquid, 85 K) | 1.66 (liquid, 203 K) | 3.19 (liquid, 273 K) | 4.94 (solid, 293 K) | – |
| X–X distance/pm | 143 | 199 | 228 | 266 | – |
| Bond dissociation enthalpy/kJ mol⁻¹ | 158.8 | 242.6 | 192.8 | 151.1 | – |
| E°/V (for X₂(g) + 2e⁻ → 2X⁻(aq)) | 2.87 | 1.36 | 1.09 | 0.54 | – |
Table 7.8Table 7.8: Atomic and Physical Properties of Halogens
| Property | F | Cl | Br | I | At a |
|---|---|---|---|---|---|
| Atomic number | 9 | 17 | 35 | 53 | 85 |
| Atomic mass/g mol-1 | 19.00 | 35.45 | 79.90 | 126.90 | 210 |
| Electronic configuration | [He]2s2 2p5 | [Ne]3s2 3p5 | [Ar]3d10 4s2 4p5 | [Kr]4d10 5s2 5p5 | [Xe]4f14 5d10 6s2 6p5 |
| Covalent radius/pm | 64 | 99 | 114 | 133 | - |
| Ionic radius X-/pm | 133 | 184 | 196 | 220 | - |
| Ionisation enthalpy/kJ mol-1 | 1680 | 1256 | 1142 | 1008 | - |
| Electron gain enthalpy/kJ mol-1 | -333 | -349 | -325 | -296 | - |
| Electronegativity b | 4 | 3.2 | 3.0 | 2.7 | 2.2 |
| Delta-Hyd H(X-)/kJ mol-1 | 515 | 381 | 347 | 305 | - |
| F2 | Cl2 | Br2 | I2 | - | |
| Melting point/K | 54.4 | 172.0 | 265.8 | 386.6 | - |
| Boiling point/K | 84.9 | 239.0 | 332.5 | 458.2 | - |
| Density/g cm-3 | 1.5 (85) c | 1.66 (203) c | 3.19 (273) c | 4.94 (293) d | - |
| Distance X-X/pm | 143 | 199 | 228 | 266 | - |
| Bond dissociation enthalpy/(kJ mol-1) | 158.8 | 242.6 | 192.8 | 151.1 | - |