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GroupSeven:TheHalogens1The HalogensThe halogens are:Fluorine F

The HalogensThe halogens are:Fluorine FChlorine Cl

The HalogensThe halogens are:Fluorine FChlorine ClBromine Br

The HalogensThe halogens are:Fluorine FChlorine ClBromine BrIodine I (Astatine At)

The Halogens

The Group 7 elements all exist as diatomic molecules. By sharing a pair of electrons between them, two atoms of a Group 7 element can both obtain complete valence shells. The HalogensThe word halogen is derived from the Greek language and means salt producer. This reflects the ability of the Group 7 elements to react with a metal forming an ionic compound or salt as the reaction product.

Sodium reacts with chlorine to form sodium chloride:sodium + chlorine sodium chlorideWrite a balanced chemical equation for the reaction:2Na(s) + Cl2(g) 2NaCl(s)The HalogensThe word halogen is derived from the Greek language and means salt producer. This reflects the ability of the Group 7 elements to react with a metal forming an ionic compound or salt as the reaction product.

Magnesium reacts with iodine to form magnesium iodide:magnesium + iodine magnesium iodideWrite a balanced chemical equation for the reaction:Mg(s) + I2(s) MgI2(s)The HalogensThe word halogen is derived from the Greek language and means salt producer. This reflects the ability of the Group 7 elements to react with a metal forming an ionic compound or salt as the reaction product.

Aluminium reacts with bromine to form aluminium bromide:aluminium + bromine aluminium bromideWrite a balanced chemical equation for the reaction:2Al(s) + 3Br2(l) 2AlBr3(s)The HalogensThe word halogen is derived from the Greek language and means salt producer. This reflects the ability of the Group 7 elements to react with a metal forming an ionic compound or salt as the reaction product.

iron reacts with chlorine to form iron(III) chloride:iron + chlorine iron(III) chlorideWrite a balanced chemical equation for the reaction:2Fe(s) + 3Cl2(g) 2FeCl3(s)The Halogens

Reactivity of the Group 7 ElementsThe reactivity of the Group 7 elements decreases while descending the Group. The Group 7 elements all react by gaining a single electron to fill their valence shell, resulting in the formation of an ion with a single negative charge.

The HalogensReactivity of the Group 7 ElementsThe reactivity of the Group 7 elements decreases while descending the Group. The Group 7 elements all react by gaining a single electron to fill their valence shell, resulting in the formation of an ion with a single negative charge.

The HalogensReactivity of the Group 7 ElementsWhile descending Group 7, the valence shell is removed further and further from the nucleus of the atom due to the addition of a complete, new electron shell.

The Halogens

Reactivity of the Group 7 ElementsThe further the valence shell is from the nucleus of the atom, the weaker the force of attraction between the positive nucleus and negative valence electrons.

The Halogens

Reactivity of the Group 7 ElementsThis means that, while descending Group 7, it becomes increasingly more difficult for the positive nucleus to attract a negative electron into the valence shell of the atom, and the reactivity of the Group 7 elements consequently decreases.

The Halogens

Reactivity of the Group 7 ElementsIn addition to this, while descending Group 7, the negative valence electrons becomes more shielded from the attractive force of the positive nucleus by the increasing number of electron shells in between the nucleus and the valence shell.

The Halogens

Reactivity of the Group 7 ElementsThis also makes it more difficult for the positive nucleus to attract a negative electron into the valence shell of the atom, and the reactivity of the Group 7 elements consequently decreases on descending the Group.

The HalogensReactivity of the Group 7 ElementsReactivity DecreasesFluorineMost ReactiveThe valence shell is close to the nucleus and is not very well shielded. It is easy for the positive nucleus to attract a negative electron into the valence shell of the atom.ChlorineBromineLeast ReactiveThe valence shell is far from the nucleus and is well shielded. It is difficult for the positive nucleus to attract a negative electron into the valence shell of the atom.IodineDisplacement Reactions

A more reactive halogen can displace a less reactive halogen from its compounds.Displacement Reactions

The addition of chlorine water to aqueous potassium bromide.Displacement Reactions

The addition of chlorine water to aqueous potassium bromide.Displacement Reactions

The addition of chlorine water to aqueous potassium bromide.Cl2(aq) + 2KBr(aq) Br2(aq) + 2KCl(aq)Cl2(aq) + 2Br-(aq) Br2(aq) + 2Cl-(aq)Displacement ReactionsThe addition of chlorine water to aqueous potassium iodide.

Displacement ReactionsThe addition of chlorine water to aqueous potassium iodide.

Displacement ReactionsThe addition of chlorine water to aqueous potassium iodide.

Cl2(aq) + 2KI(aq) I2(aq) + 2KCl(aq)Cl2(aq) + 2I-(aq) I2(aq) + 2Cl-(aq)Displacement ReactionsThe addition of bromine water to aqueous potassium iodide.

Displacement ReactionsThe addition of bromine water to aqueous potassium iodide.

Displacement ReactionsThe addition of bromine water to aqueous potassium iodide.

Br2(aq) + 2KI(aq) I2(aq) + 2KBr(aq)Br2(aq) + 2I-(aq) I2(aq) + 2Br-(aq)Displacement ReactionsThe addition of bromine water to aqueous potassium chloride.

Displacement ReactionsThe addition of bromine water to aqueous potassium chloride.

There is no observed chemical reaction.The HalogensUses of the halogens:Fluorine: Compounds of fluorine (e.g. potassium fluoride, formula KF) are added to toothpaste and drinking water to strengthen tooth enamel and therefore reduce tooth decay. Fluorine is used in the manufacture of the non-stick polymer Teflon. Fluorine is used in the manufacture of chlorofluorocarbons (CFCs) which are used in refrigerators and air-conditioning units. Fluorine is used in the manufacture of the anaesthetic Halothane.

The structural formula (left) and ball-and-stick structure (right) of Halothane.The HalogensUses of the halogens:Chlorine: Chlorine is used in the manufacture of bleach, disinfectants and antiseptics, for example, TCP. Chlorine is used in the manufacture of the polymer PVC. Chlorine is used in the manufacture of chlorofluorocarbons (CFCs) which are used in refrigerators and air-conditioning units.

The structural formula (left) and ball-and-stick structure (right) of TCP.

The HalogensUses of the halogens:Bromine: Silver bromide (formula AgBr) is sensitive to light (photosensitive) and is therefore used in the manufacture of photographic films. When light strikes the photographic film, the silver ions are reduced to form small dark crystals of silver metal. This produces the negative from which the actual photograph is developed:Ag+ + e Ag Bromine is also used in the manufacture of pesticides and teargas.

The HalogensUses of the halogens:Iodine: Iodine is required by the human body to make the hormone thyroxine. Thyroxine is produced by the thyroid gland and affects the bodys basal metabolic rate, protein synthesis and sensitivity to other hormones such as insulin. Iodine is used to make the mild antiseptic tincture of iodine that is used in hospitals.The structural formula of thyroxine.

The HalogensUses of the halogens:Iodine: Iodine is required by the human body to make the hormone thyroxine. Thyroxine is produced by the thyroid gland and affects the bodys basal metabolic rate, protein synthesis and sensitivity to other hormones such as insulin. Iodine is used to make the mild antiseptic tincture of iodine that is used in hospitals.Theball-and-stick structure of thyroxine.

The four purple spheres represent iodine atoms.