Group 7- the halogens

group 7 everything 

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  • Created by: melissa
  • Created on: 05-04-12 11:35

Group 7 overview

F

Cl

Br

I

At

atomic radius increases down the group. Number of shells increase, outer electron futher from nucleus hence more shielding thus less attraction.

ionic radius increases down the group. Ionic radis is larger than atomic radius due to nuclear charge and electrons been pulled in less tightly


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overview continued

F

Cl

Br

I

At

electron affinity- the ability to attract an electron and become a negative ion decreases down the group. F is unusually low due to the incoming electron is entering a shell futher away from the nucleus. More shielded and hence electron less strongly attracted.

electronegativity decreases down a group because the atomic radius increases so electrons in a covalent bond are attracted less to the halogen as its atomic number increases.

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overview continued...

F

Cl

Br

I

At

boiling point (volatility) increases down a group. All halogens are diatomic so they have weak intermolecular forces (VDWs). These increase with increasing number of electrons due to the possibility that a tempory dipole will form

reactivity decreases down a group due to decreasing electron affinity and so ability to attract electrons and decreasing bond dissociation enthalpy.

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F

Cl

Br

I

At

bond disociation is a measure of how easy it is to break X-X. 

decreases down a group because atomic radius increases and so the attraction between the nbucleus and the electrons will decrease with increasing bond length.

F-F is unexpected weak because the F atom is small so the lone pair of electrons in F-F are closer together so they repel each each other strongly weakening the bond.

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Halogens as oxidising agents

oxidising agent... is a substance that removes electrons from another reactant in a redox reaction. The oxidising agent is reduced by taking electrons onto itself and the reactant is oxidsed by having its electrons taken away.

F2 is the next strongest oxidising agent

Cl2  is the next strongest oxidising agent as it can oxidise Br- and I- then it decreases...

Br2  can only oxidise I-

I2  can't oxidise I- or Br-

 

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Reducing power of Halide ions

2HBr + H2SO4   Br2 + SO4 + H2O

2HI + H2SO4   I2 + SO4 + H2O

8HI + H2SO4   4I2 + 4H2O + H2S

Concentrated sulphuric acid

First reaction = acid base

Halide acting as reducing agent because they are losing an electron

Reducing power increases down the group due to increasing ion size. Electrons further away, more shielding, less energy to lose. Also H-X bond weakens. 

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