bài tập và lý thuyết Halogens

41
41.1
41.2
41.3

The Halogens

Characteristic Properties of the Halogens
Variation in Properties of the Halogens
Comparative Study of the Reactions of
Halide Ions
41.4 Acidic Properties of Hydrogen Halides and
the Anomalous Behaviour of Hydrogen
Fluoride


41.1
Characteristic
Properties of the
Halogens


41.1 Characteristic Properties of the Halogens (SB p.78)

Introduction
•

Group VIIA elements include
 fluorine
 chlorine
 bromine

 iodine
 astatine


41.1 Characteristic Properties of the Halogens (SB p.78)

Introduction
•

Astatine
 not much is known
 radioactive


41.1 Characteristic Properties of the Halogens (SB p.78)

Introduction
•

Group VIIA elements
 also called halogens


41.1 Characteristic Properties of the Halogens (SB p.78)

The halogens


41.1 Characteristic Properties of the Halogens (SB p.79)

Introduction
•

All halogens
 outermost shell electronic
configuration of ns2np5
 one electron short of the octet
electronic configuration


41.1 Characteristic Properties of the Halogens (SB p.79)

Introduction
•

In the free elemental state
 form diatomic molecules
 complete their octets by sharing their
single unpaired p electrons


41.1 Characteristic Properties of the Halogens (SB p.79)

Introduction
•

When halogens react with other elements
 complete their octets
 depending on the electronegativity of
the element

41.1 Characteristic Properties of the Halogens (SB p.79)

Introduction
•

Either
 gaining an additional electron to form
halide ions
 or sharing their single unpaired p
electrons to form single covalent
bonds


41.1 Characteristic Properties of the Halogens (SB p.79)

chlorine

Appearances of halogens at room
temperature and pressure: chlorine


41.1 Characteristic Properties of the Halogens (SB p.79)

bromine
Appearances of halogens at room
temperature and pressure: bromine

41.1 Characteristic Properties of the Halogens (SB p.79)

iodine
Appearances of halogens at room
temperature and pressure: iodine


41.1 Characteristic Properties of the Halogens (SB p.79)

High Electronegativity
Electronegativity is the relative tendency
of an atom to attract bonding electrons
towards itself in a covalent bond.


41.1 Characteristic Properties of the Halogens (SB p.79)

High Electronegativity
•

All halogens
 high electronegativity values
 high tendency to attract an additional
electron to achieve the stable octet
electronic configuration
 highest among the elements in the
same period


41.1 Characteristic Properties of the Halogens (SB p.79)

Electronegativity values of halogens
Halogen

Electronegativity value

F

4.0

Cl

3.0

Br

2.8

I

2.5

At

2.2


41.1 Characteristic Properties of the Halogens (SB p.79)

High Electron Affinity

Electron affinity is the enthalpy change
when one mole of electrons is added to
one mole of atoms or ions in the gaseous
state.


41.1 Characteristic Properties of the Halogens (SB p.79)

High Electron Affinity
•

Its value
 indicates the ease of formation of
anions


41.1 Characteristic Properties of the Halogens (SB p.79)

High Electron Affinity
•

All halogens
 negative values of electron affinity
 high tendency to attract an additional
electron to form the respective halide
ions


41.1 Characteristic Properties of the Halogens (SB p.79)

Electron affinities of halogens
Halogen

Electron affinity (kJ mol–1)

F

–348

Cl

–364

Br

–342

I

–314

At

–285


41.1 Characteristic Properties of the Halogens (SB p.80)

Bonding and Oxidation State
•

Halogens
 gain an additional electron to form
the halide ions
 combine with metals to form metal
halides
 held together by ionic bonding


41.1 Characteristic Properties of the Halogens (SB p.80)

Bonding and Oxidation State
•

The oxidation states of the halogens = –1


41.1 Characteristic Properties of the Halogens (SB p.80)

Bonding and Oxidation State
•

The halogen atoms
 share their unpaired p electrons with
a non-metallic atom
 form a covalent bond


41.1 Characteristic Properties of the Halogens (SB p.80)

Bonding and Oxidation State
•

Halogens (except fluorine)
 exhibit an oxidation state of –1 or +1
in the covalent molecules formed
 depend on the electronegativity of
the
elements that are covalently
bonded
with the halogens


41.1 Characteristic Properties of the Halogens (SB p.80)

Bonding and Oxidation State
•

All halogens (except fluorine)
 can expand their octets of electrons
by utilizing the vacant, low-lying d
orbitals