By: Hiromi Sarah Fukuzaki

GROUP 7A ELEMENTSSECTION 20.7

Also known as the “Halogens”Valence electron configuration s2p5.Consists of Fluorine, Chlorine, Bromine, Iodine and Astatine. High electronegativity values, tends to form covalent bonds

with other nonmetals & ionic with metals (lower oxidation state; if higher, polar covalent bonds).

BACKGROUND INFO

Not considered free elements, instead they are foundas halide ions due to their reactivity.

MORE BACKGROUND INFO

Negligible due to its radioactivity(isotopes) and short life (half-life 8.3 hours)

Can be prepared through this kind of reaction: H2(g) + X2(g) 2HX(g)

Violent reaction occurs when fluorine and hydrogen are mixed.Hydrogen and chlorine can coexist in the dark, exposing these

to ultra-violet light causes an explosively fast reaction. (hydrogen-chlorine cannon.)

Bromine and iodine react slower with hydrogenHydrogen Halides can also be created by treating a halide salts

with acid. CaF2(s) + H2SO4(aq) CaSO4(s) + 2HF(g) 2NaCl(s) + H2SO4(aq) Na2SO4(s) + 2HCl(g)

Oxidizing agents cannot be used to create hydrogen halides. Ex: sulfuric acid. Phosphoric can be used to form hydrogen halides

HYDROGEN HALIDES

High boiling point for hydrogen fluoride. (Hydrogen bonding)When dissolved in water, hydrogen halides behave as acids.

Dissolve completely except for hydrogen fluoride. Water is a stronger base for all except fluorine.

PROPERTIES OF HYDROGEN HALIDES

Cannot be determined in water, but can in pure acetic acid. H–I > H–Br > H–Cl > H–FStrongest acid --- weakest acid

Why is HF the only weak acid in group 7A? Must look at the dissociation equilibrium equation

Acid strength depends on Ka Small Ka = weak acid

K depends on △G∘

△G∘ depends on △H∘ & △S∘

To explain acid dissociation must know the factors determining △H∘ & △S∘. (mostly entropy since -△S∘ is

unfavorable.)

ACID STRENGTH

Most important of the hydrohalic acids (aqueous solutions of hydrogen halides).

Hydrofluoric acid used to cut glass Done by reacting hydrofluoric acid with silica to form SiF4

SiO2(s) + 4HF(aq) SiF4(g) + 2H2O(l)

HYDROCHLORIC ACID

All halogens, except fluorine, combine with oxygen atoms to form a series of oxyacids.

Strength of the acids vary depending on the number of oxygens attached to the halogen.

OXYACIDS

OXYCHLORO ANION STRUCTURES

Formed when chlorine gas is dissolved in cold water.Cl2(aq) + H2O(l) ⇌ HOCl(aq) + H+(aq) + Cl-(aq)

Reaction is called a disproportional reaction, due to the reduction and oxidation taking place.

HYPOCHLOROUS ACID

OF2

Halogens react with each other to form interhalogen compounds. Abn n = 1,3,5 or 7 and A is the larger halogen.

Compound structures can be predicted by the VSEPR model. Interhalogens are volatile, highly reactive that act as a strong

oxidizing agent.

OTHER HALOGEN COMPOUNDS