ionic bonding
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ionic bonding is the bonding of ions to form molecule.
Transcript of ionic bonding
What is chemical bond?What is chemical bond?
Chemical bond or chemical bonding Chemical bond or chemical bonding may be defined as the force or, more may be defined as the force or, more
accurately, the energy, that hold atoms accurately, the energy, that hold atoms together in chemical compounds.together in chemical compounds.
There are two principal classes of There are two principal classes of chemical bonding, namely chemical bonding, namely ionic ionic bondingbonding and and covalent bondingcovalent bonding..
Valence electrons
Valence electrons are those in the outermost shell of an atom. The remaining electrons are the core
electrons.
Na (2, 8, 1)
Core electronValence electron
Core electron
Valenceelectron
Cl (2, 8, 7)
Core electronValence electron
Core electron
Valenceelectron
Lewis symbol or Lewis dot symbol is the symbol of an element that includes dots represents the valence electrons of an atom of the element. Core electrons are not shown in the Lewis symbol.
Lewis symbol
For an atom with four or less valence For an atom with four or less valence electrons, these electrons are displayed electrons, these electrons are displayed singly around the four sides of the symbol singly around the four sides of the symbol of the element. of the element. If there more than four valence electrons, If there more than four valence electrons, some of their dots are paired.some of their dots are paired.
Li Be B C N O F Ne:. . ... . .. . ..
. .. .: :::. :
::
::
Group 1 2 13 14 1 5 16 1 7 1 8
or IA IIA IIIA IVA VA VIA VIIA VIIIA
Na+
Mg2+
Na+ Mg :O:
::
2+ 2_:N:
::
3_:C:
::
4_:F:
::
_
:O:
::
2_:N:
::
3_:C:
::
4_:F:
::
_or
The creation of ions is indicated by removing dots from or adding them to Lewis symbol and also by writing the net electric charge of the ion as a right superscript.
Combination of Lewis symbol of cation and anion in ionic compound is a Lewis structure of ionic compound.
Na :Cl:
::
+ _Mg :O:
::
2+ 2_
Mg2+
:Cl::
:
_2 Na
+:O:
::
2_2
NaCl MgO
MgCl2 Na2O
The outermost shell of electron configurations of ions or atoms similar to those of noble gases, except helium, always contains eight electrons. This is usually said as an octet configuration. Ions and atoms with electron configuration similar to those of noble gases are said obeying octet configuration or octet rule. These atoms and ions are usually stable.
Classification of ionClassification of ion Ion
Cation Anion
Simplecation
Simpleanion
Polyatomiccation
Polyatomic anion
Na+
Mg2+
Al3+
NH4+
PH4+
Cl-
O2-
N3-
NO3-
SO42-
PO43-
Classification of ionic compoundClassification of ionic compound(1) ionic compound consists of simple cation and
simple anion.Examples: NaCl, MgCl2, MgO, K2O
(2) ionic compound consists of simple cation and polyatomic anion. Examples: NaNO3, MgSO4, Na2SO4
(3) ionic compound consists of polyatomic cation and simple anion.Examples: NH4Cl, NH4Br, PH4I
(4) ionic compound consists of polyatomic cation and polyatomic anion.Examples: NH4NO3, (NH4)2SO4
Ionic bonding Ionic bonding An ionic bonding is a An ionic bonding is a chemical bonding formed by chemical bonding formed by the electrostatic attraction the electrostatic attraction between positive and between positive and negative ions.negative ions.
Formation of ionic compoundFormation of ionic compound
(1)(1) Formation of ionic compounds Formation of ionic compounds directly directly from cation and anion such as given in from cation and anion such as given in the following examplesthe following examples
NaNa22SOSO44((aqaq) + BaCl) + BaCl22((aqaq) → ) → 2NaCl(2NaCl(aqaq) + BaSO) + BaSO44((ss) )
NaNa22COCO33((aqaq) + Ba(NO) + Ba(NO33))22((aqaq) → ) → 2NaNO2NaNO33((aqaq) + BaCO) + BaCO33((ss))
(2) (2) Formation of ionic compounds Formation of ionic compounds indirectlyindirectly from elements which from elements which involves transfer electron from involves transfer electron from one one element to other element element to other element such as such as given in the following given in the following example.example.
Na(g) + Cl(g) → NaCl(Na(g) + Cl(g) → NaCl(gg))
Na+
:Cl:
::
_Na . + . Cl:
::
an ion pair
Na+
:Cl:
::
_Na . + .Cl:
::
(2, 8, 1) (2, 8, 7) (2, 8) (2, 8, 8)
Formation of ionic compound is accompanied with the change of electron configuration of species
involved in the reaction .
Na (2, 8, 1) Cl (2, 8, 7) Na+ (2, 8) Cl- (2, 8, 8)
Formation of ionic compound is also Formation of ionic compound is also accompanied with the change of the size accompanied with the change of the size
of species involved in the reaction .of species involved in the reaction .
+
Na(g) Na+(g)Cl(g) Cl-(g)
Structure of ionic Structure of ionic compound compound In the gas In the gas phase, an ionic phase, an ionic compound may compound may exist as an ion exist as an ion pair. Sodium pair. Sodium chloride, for chloride, for example, exists example, exists as an ion pair.as an ion pair.
Na+ Cl-
In the solid phase there are many Na+ and Clˉ ions forming regular arrangement of
periodic alternating positive and negative ions. The 2-dimension structure of NaCl is
as follows.
(a) (b)
Cl-
Na+ Na+
Cl-
The 3-dimension unit cell of NaCl crystal is a face centered cubic (fcc)
= Cl- = Na+
CornerFace center Face center Corner
(a) (b)Side center Side center
Energetic of ionic compoundEnergetic of ionic compound
Gaseous ionic compound may be formed from Gaseous ionic compound may be formed from its gaseous atoms if this formation is its gaseous atoms if this formation is energetically favorable (accompanied with energetically favorable (accompanied with release of some energy).release of some energy). For the formation taking place at constant For the formation taking place at constant pressure, the energy involved is expressed in pressure, the energy involved is expressed in enthalpy (enthalpy (HH) or the ) or the heat content of a system at heat content of a system at constant pressureconstant pressure. . Formation of ionic compound is energetically Formation of ionic compound is energetically favorable if it is accompanied with decreasing of favorable if it is accompanied with decreasing of enthalpy (Δenthalpy (ΔHH < 0; Δ < 0; ΔHH is the enthalpy changing). is the enthalpy changing).
Formation of gaseous NaCl from Formation of gaseous NaCl from gaseous sodium and chlorine atoms gaseous sodium and chlorine atoms
involve three processes:involve three processes:
(1)(1) ionization of sodium atom to ionization of sodium atom to sodium ion which is accompanied sodium ion which is accompanied
with absorption of some energy. with absorption of some energy. The energy absorbed is The energy absorbed is
ionization ionization energy (energy (IEIE).).
Na(Na(gg) → Na+() → Na+(gg) + ) + ee IEIE = 495 kJ/mol = 495 kJ/mol
(2)(2) ionization of chlorine atom to chloride ion ionization of chlorine atom to chloride ion which is accompanied with release of some which is accompanied with release of some energy. The energy energy. The energy involved in this processinvolved in this process is is called electron affinitycalled electron affinity ( (EEAA).).
Cl(g) + Cl(g) + ee → Clˉ( → Clˉ(gg) ) EAEA = -348.5 kJ/mol = -348.5 kJ/mol
(3)(3) formation of ionic bonding in an ion pair of formation of ionic bonding in an ion pair of gaseous NaCl which is accompanied with gaseous NaCl which is accompanied with release of some energy.release of some energy.
Na+(Na+(gg) + Clˉ(g) → NaCl() + Clˉ(g) → NaCl(gg) ) Δ ΔHHipip = -450.2 = -450.2 kJ/molkJ/mol
ΔΔHHip ip is enthalpy changing for the formation of is enthalpy changing for the formation of ion pair (ip).ion pair (ip).
The enthalpy changing for the formation of gaseous ionic pair of NaCl (ΔHf, f = formation) from its gaseous atoms can be calculated as follows:
Na(g) Na+(g) + e IE = 495 kJ/mol
Cl(g) + e Cl-(g) EA = -348.5 kJ/mol
Na+(g) + Cl-(g) NaCl(g) Hip = -450.2 kJ/mol
Na(g) + Cl(g) NaCl(g) Hf = -303.7 kJ/mol
Properties of ionic compoundsProperties of ionic compounds (1) (1) Ionic compounds tend to have high Ionic compounds tend to have high melting point because the ionic bonding melting point because the ionic bonding in this compound is quite strongin this compound is quite strong. .
In NaCl crystal, for example, there are In NaCl crystal, for example, there are many Namany Na++ cations and Clˉ anions where cations and Clˉ anions where each Na+ ion is attracted to many each Na+ ion is attracted to many surrounding Clˉ anions and each Clˉ surrounding Clˉ anions and each Clˉ anion anion is attracted to many surrounding is attracted to many surrounding NaNa++ cations. cations. For sodium chloride to melt For sodium chloride to melt every every ionic attraction in the crystal must ionic attraction in the crystal must be be overcome. This process requires overcome. This process requires large large amount of energy so that NaCl has amount of energy so that NaCl has high high melting point. melting point.
Melting point of some alkali halides
Alkali Alkali halidehalide
m.p. m.p. (°C)(°C)
Alkali Alkali halidehalide
m.p. m.p. (°C)(°C)
NaFNaFNaClNaClNaBrNaBrNaINaI
993993801801747747651651
KFKFKClKClKBrKBrKIKI
846846770770730730686686
(2) In the solid state, ionic (2) In the solid state, ionic compounds do not conduct compounds do not conduct electricity because the attractive electricity because the attractive force between cations and anions force between cations and anions
prevent the movement of ions prevent the movement of ions through the crystal. When the through the crystal. When the solid melted, however, the ions solid melted, however, the ions become free to move about and become free to move about and the the liquid conducts electricity liquid conducts electricity quite quite well.well.
(3) Ionic compounds are usually hard (3) Ionic compounds are usually hard but brittle substances. When struck but brittle substances. When struck by a hammer the layer of ions in the by a hammer the layer of ions in the crystal moves. crystal moves.
The slight movement The slight movement of a layer of of a layer of ion within crystal suddenly places ion within crystal suddenly places ions of the same charge next to ions of the same charge next to each each other, and for that instant other, and for that instant there are there are large repulsive forces that large repulsive forces that split the split the solid and crystal of ionic solid and crystal of ionic compound compound shatters. shatters.
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A blowis struck
(a) (b) (c)
(4) Ionic compounds dissolves in (4) Ionic compounds dissolves in polar solvent such as water. polar solvent such as water.
NaCl, for example, dissolves very NaCl, for example, dissolves very easily in water. easily in water. The solution of The solution of ionic ionic compound in water conducts compound in water conducts electricity because in the solution electricity because in the solution ions move freely.ions move freely. Ionic compound Ionic compound does not dissolve in most organic does not dissolve in most organic compounds such as acetone, compounds such as acetone, alcohol, ether, and carbon alcohol, ether, and carbon tetrachloride.tetrachloride.
SummarySummary(1)(1) Chemical bond or chemical bonding Chemical bond or chemical bonding may may
be defined as the force or, more be defined as the force or, more accurately, the energy, that hold atoms accurately, the energy, that hold atoms together in chemical compounds. together in chemical compounds.
(2)(2) There are two principal classes of There are two principal classes of chemical bonding, namely ionic bonding chemical bonding, namely ionic bonding and covalent bonding. and covalent bonding.
(3)(3) Not all of electrons in an atom participate Not all of electrons in an atom participate in chemical bonding. For main group in chemical bonding. For main group elements, only valence electrons play a elements, only valence electrons play a fundamental role in chemical fundamental role in chemical bonding. bonding.
((4) In an ionic compound, the ions 4) In an ionic compound, the ions present tend to attain an electron present tend to attain an electron configuration similar to those of configuration similar to those of noble gases or octet configuration. noble gases or octet configuration. These ions with such These ions with such electron electron configuration obey the octet rule. configuration obey the octet rule.
(5) Simple ionic compound consists of (5) Simple ionic compound consists of simple cation and simple anion. simple cation and simple anion. Simple ionic compounds form only Simple ionic compounds form only between very active metallic between very active metallic elements and very active elements and very active nonmetallic elements.nonmetallic elements.
(6) An ionic bonding is a chemical (6) An ionic bonding is a chemical bonding formed by the bonding formed by the electrostatic attraction between electrostatic attraction between positive and negative ions.positive and negative ions.
(7) Ionic compounds tend to have (7) Ionic compounds tend to have high melting point, do not conduct high melting point, do not conduct
electricity in the solid phase, electricity in the solid phase, usually hard but brittle usually hard but brittle substances.substances.
Ionic compounds dissolves in Ionic compounds dissolves in polar solvent such as water.polar solvent such as water.
