Group 17 Halogens Flashcards

Comprehensive vocabulary flashcards covering Group 17 elements (halogens), their physical trends, chemical reactions, and identification tests.

Halogens

Group 7 (17) non-metals on the right-hand side of the Periodic Table that exist as diatomic molecules: $F_2$, $Cl_2$, $Br_2$, and $I_2$.

Fluorine Appearance

A pale yellow gas at room temperature.

Chlorine Appearance

A greenish gas at room temperature.

Bromine Appearance

A red-brown liquid at room temperature.

Iodine Appearance

A black solid at room temperature.

F-F Bond Energy

Unexpectedly weak at $158\,kJ\,mol^{-1}$ due to repulsion between non-bonding electrons in the small fluorine atom.

Atomic Radius Trend

The radius increases going down Group 17 because each element has one extra filled main level of electrons compared with the one above it.

Electronegativity

A measure of the ability of an atom to attract electrons, or electron density, towards itself within a covalent bond.

Electronegativity Trend

Decreases going down Group 17 because shared electrons are further from the nucleus and shielded by more inner shells, which outweighs the increasing nuclear charge.

Melting and Boiling Points Trend

Increase going down Group 17 because larger atoms have more electrons, which makes the van der Waals forces between molecules stronger.

Oxidising Agent

A species that gains electrons and is itself reduced during a redox reaction.

Oxidising Ability Trend

Increases going up the group, making fluorine one of the most powerful oxidising agents known.

Displacement Reaction

A reaction where a halogen reacts with a metal halide in solution, displacing a less reactive halide ion (e.g., $Cl_2(aq) + 2NaBr(aq) \rightarrow Br_2(aq) + 2NaCl(aq)$).

Reducing Ability Trend

Increases going down Group 17 as the ionic radius increases ($0.133\,nm$ for $F^-$ to $0.215\,nm$ for $I^-$), making it easier for the outer electron to be lost due to weaker nuclear attraction.

Reaction of NaCl with concentrated sulfuric acid

An acid-base reaction (not redox) producing steamy fumes of $HCl(g)$ and solid $NaHSO_4(s)$. $NaCl(s) + H_2SO_4(l) \rightarrow NaHSO_4(s) + HCl(g)$

Reaction of NaBr with concentrated sulfuric acid

A redox reaction producing steamy fumes of $HBr$, brown fumes of $Br_2$, and colourless $SO_2$. $2H^+ + 2Br^- + H_2SO_4(l) \rightarrow SO_2(g) + 2H_2O(l) + Br_2(l)$

Reaction of NaI with concentrated sulfuric acid

A strong redox reaction producing $HI$, black solid $I_2$, the "bad egg" smell of $H_2S$ gas, yellow solid sulfur, and $SO_2$. $8H^+ + 8I^- + H_2SO_4(l) \rightarrow H_2S(g) + 4H_2O(l) + 4I_2(s)$

Silver Nitrate Test

Used to identify halides; acidified $AgNO_3$ forms a white ppt with $Cl^-$, cream ppt with $Br^-$, and pale yellow ppt with $I^-$. Silver fluoride is soluble and forms no precipitate.

Silver Chloride Solubility

A white precipitate that dissolves in dilute ammonia solution.

Silver Bromide Solubility

A cream precipitate that dissolves only in concentrated ammonia solution.

Silver Iodide Solubility

A pale yellow precipitate that is insoluble in concentrated ammonia solution.

Nitric Acid in Halide Tests

Added to halide solutions before silver nitrate to remove carbonate or hydroxide impurities that would interfere by forming insoluble silver carbonate or silver hydroxide.

Disproportionation

A type of redox reaction where the oxidation state of some atoms of the same element increases and others decrease (e.g., $Cl_2 + H_2O \rightleftharpoons HClO + HCl$).

Chloric(I) Acid (HClO)

An oxidising agent and bleach formed when chlorine reacts with water; it kills bacteria in water supplies and swimming pools.

Reaction of Chlorine with Cold Dilute Sodium Hydroxide

A disproportionation reaction producing sodium chlorate(I) ($NaClO$), the active ingredient in bleach. $Cl_2(g) + 2NaOH(aq) \rightarrow NaClO(aq) + NaCl(aq) + H_2O(l)$