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# Chemical Ideas: The Periodic Table 11.3a ## The p-block - Group 7 The halogens are the elements in Group 7 of the periodic table (Figure 3). All halogen atoms have seven electrons in the outer shell. They are the most reactive group of non-metals and are not found naturally in elemental form....

# Chemical Ideas: The Periodic Table 11.3a ## The p-block - Group 7 The halogens are the elements in Group 7 of the periodic table (Figure 3). All halogen atoms have seven electrons in the outer shell. They are the most reactive group of non-metals and are not found naturally in elemental form. They are found in compounds like calcium fluoride and sodium chloride. Fluorine, chlorine, bromine, iodine, and astatine are halogens. Fluorine and chlorine are most abundant, while bromine is less abundant, and iodine is scarce. Astatine is artificially produced. All are diatomic molecules (e.g., F₂, Br₂). **Figure 4:** Shows covalent bonding in chlorine molecules. **In compounds, a halogen atom achieves stability by:** * Gaining an electron from a metal atom, forming a halide ion in an ionic compound (Figure 5). * Sharing an electron from another non-metal atom in a covalently bonded compound (Figure 6). **Figure 5:** Shows Halogens can achieve eight outer electrons by forming an ion (e.g., Cl⁻) via ionic bonding. **Figure 6:** Shows Halogens can achieve eight outer electrons by covalent bonding. ## Physical Properties of the Halogens **(Table 1):** Shows some properties of the halogens. Includes element, formula, appearance, melting point (K), boiling point (K), solubility at 298 K (g per 100 g of water) and reaction with water. **Trends:** * **Color:** Becomes darker as you go down the group. * **Melting/Boiling Point:** Increases as you descend the group. * **State:** Changes from gases to liquids and to solid at room temperature. * **Volatility:** Decreases down the group. * **Solubility:** No clear trend as you go down the group. More soluble in organic solvents than in water. **Figure 7:** Halogens dissolved in water— chlorine is pale green, bromine is orange/yellow, and iodine is brown. **Figure 8:** Halogens dissolved in cyclohexane—chlorine is pale green, bromine is orange/brown/red, and iodine is violet. ## Chemical Properties of the Halogens Halogens are reactive elements. They remove electrons from other elements to complete their outer shell. E.g., 2Na(s) + Cl₂(g) → 2NaCl(s) The halogens gain electrons to become negative ions. The top of the group is most reactive and strongest oxidizing agents. **Figure 9:** Shows core charges and outer shells of electrons in fluorine and chlorine. * **Fluorine:** The core is very close to the outer electron making the attraction for the electron stronger. This makes fluorine very reactive. * **Chlorine:** The outer shell is further from the core making the attraction for the extra electron weaker. This makes chlorine less reactive than fluorine. This trend continues down the halogen group. ## Reactions with Halide Ions * Adding chlorine to iodide solution creates a reaction producing a solution in which iodine is produced. Pale green to brown. * Adding bromine solution to iodide ions produces an orange/yellow to brown reaction producing iodine. * These are displacement reactions as a halogen displaces another halogen from a compound.. * They are also redox reactions where both oxidation and reduction reactions occur in the same reaction. Bromine gains electrons to be reduced while iodine loses electrons and is oxidized. **(Table 2):** Shows if halogens displace other less reactive halides in reactions. ## Reactions of Halide Ions with Silver Ions When two solutions mix and a solid precipitates. Silver halides are precipitated when a silver solution is added to solutions of chloride, bromide, or iodide ions. (formula: Ag⁺(aq) + X⁻(aq) → AgX(s) **(Figure 10):** Shows the colors of the following precipitates: silver chloride, silver bromide, and silver iodide. The colors can be difficult to distinguish. **(Figure 11):** Shows Ammonia solution added to the precipitates. ## The Lowest Point on Earth (Figure 1): Shows a person floating in the Dead Sea. The Dead Sea is the lowest point on Earth due to high salinity of water (350 gdm⁻³ compared to 40 gdm⁻³ in ocean water). (Figure 2) showing the location of the Dead Sea). It’s a vast evaporating basin with no outflow resulting in accumulation of large quantities of salts. Surveys suggest around 43 billion tonnes of salts with a relatively high concentration of bromides. ## Summary Questions (various) These relate to writing equations and stoichiometry. Table and figure references included