Everything about Ionic Bond totally explained
An
ionic bond (or
electrovalent bond) is a type of
chemical bond that can often form between
metal and
non-metal ions (or
polyatomic ions such as
ammonium) through
electrostatic attraction. In short, it's a bond formed by the attraction between two oppositely charged ions.
The metal donates one or more
electrons, forming a positively charged ion or
cation with a stable
electron configuration. These electrons then enter the non metal, causing it to form a negatively charged ion or
anion which also has a stable electron configuration. The electrostatic attraction between the oppositely charged ions causes them to come together and form a bond.
For example, common
table salt is
sodium chloride. When sodium (Na) and chlorine (Cl) are combined, the
sodium atoms each lose an electron, forming a cation (Na
+), and the
chlorine atoms each gain an electron to form an anion (Cl
-). These ions are then attracted to each other in a 1:1 ratio to form sodium chloride (NaCl).
» Na + Cl → Na
+ + Cl
- → NaCl
The removal of electrons from the atoms is endothermic and causes the ions to have a higher energy. There may also be energy changes associated with breaking of existing bonds or the addition of more than one electron to form anions. However, the attraction of the ions to each other lowers their energy.
Ionic bonding will occur only if the overall energy change for the reaction is favourable – when the bonded atoms have a lower energy than the free ones. The larger the resulting energy change the stronger the bond. The low
electronegativity of metals and high electronegativity of non-metals means that the energy change of the reaction is most favorable when metals lose electrons and non-metals gain electrons.
Pure ionic bonding isn't known to exist. All ionic bonds have a degree of
covalent bonding or
metallic bonding. The larger the difference in
electronegativity between two atoms, the more ionic the bond. Ionic compounds conduct
electricity when molten or in solution. They generally have a high
melting point and tend to be soluble in water.
Polarization effects
Ions in
crystal lattices of purely ionic compounds are
spherical; however, if the positive ion is small and/or highly charged, it'll distort the electron cloud of the negative ion. This
polarization of the negative ion leads to a build-up of extra charge density between the two
nuclei, for example, to partial covalency. Larger negative ions are more easily polarized, but the effect is usually only important when positive ions with
charges of 3+ (for example, Al
3+) are involved (for example, pure AlCl
3 is a covalent molecule). However, 2+ ions (Be
2+) or even 1+ (Li
+) show some polarizing power because their sizes are so small (for example, LiI is ionic but has some covalent bonding present).
Ionic structure
Ionic compounds in the solid state form a continuous ionic lattice structure in an
ionic crystal. The simplest form of ionic crystal is a
simple cubic. This is as if all the atoms were placed at the corners of a cube. This
unit cell has a weight that's the same as 1 of the atoms involved. When all the ions are approximately the same size, they can form a different structure called a
face-centered cubic (where the weight is 4
atomic weight), but, when the ions are different sizes, the structure is often
body-centered cubic (2 times the weight). In ionic lattices the
coordination number refers to the number of connected ions.
Ionic versus covalent bonds
In an ionic bond, the atoms are bound by attraction of opposite ions, whereas, in a
covalent bond, atoms are bound by sharing electrons. In covalent bonding, the
molecular geometry around each atom is determined by
VSEPR rules, whereas, in ionic materials, the geometry follows maximum
packing rules.
Electrical conductivity
Ionic substances in solution conduct electricity because the ions are free to move and carry the electrical charge from the anode to the cathode.
Ionic substances conduct electricity when molten because atoms (and thus the electrons) are mobilised. Electrons can flow directly through the ionic substance in a molten state.
Substances in ionic form
Cations>
| Stock System Name |
Formula |
Historic Name |
| Simple Cations |
| Aluminium |
Al3+ |
|
| Barium |
Ba2+ |
|
| Beryllium |
Be2+ |
|
| Caesium |
Cs+ |
|
| Calcium |
Ca2+ |
|
| Chromium(II) |
Cr2+ |
Chromous |
| Chromium(III) |
Cr3+ |
Chromic |
| Chromium(VI) |
Cr6+ |
Chromyl |
| Cobalt(II) |
Co2+ |
Cobaltous |
| Cobalt(III) |
Co3+ |
Cobaltic |
| Copper(I) |
Cu+ |
Cuprous |
| Copper(II) |
Cu2+ |
Cupric |
| Copper(III) |
Cu3+ |
|
| Gallium |
Ga3+ |
|
| Gold(I) |
Au+ |
|
| Gold(III) |
Au3+ |
|
| Helium |
He2+ |
(Alpha particle) |
| Hydrogen |
H+ |
(Proton) |
| Iron(II) |
Fe2+ |
Ferrous |
| Iron(III) |
Fe3+ |
Ferric |
| Lead(II) |
Pb2+ |
Plumbous |
| Lead(IV) |
Pb4+ |
Plumbic |
| Lithium |
Li+ |
|
| Magnesium |
Mg2+ |
|
| Manganese(II) |
Mn2+ |
Manganous |
| Manganese(III) |
Mn3+ |
Manganic |
| Manganese(IV) |
Mn4+ |
Manganyl |
| Manganese(VII) |
Mn7+ |
|
| Mercury(II) |
Hg2+ |
Mercuric |
| Nickel(II) |
Ni2+ |
Nickelous |
| Nickel(III) |
Ni3+ |
Nickelic |
| Potassium |
K+ |
|
| Silver |
Ag+ |
|
| Sodium |
Na+ |
|
| Strontium |
Sr2+ |
|
| Tin(II) |
Sn2+ |
Stannous |
| Tin(IV) |
Sn4+ |
Stannic |
| Zinc |
Zn2+ |
|
| Polyatomic Cations |
| Ammonium |
NH4+ |
|
| Hydronium |
H3O+ |
|
| Nitronium |
NO2+ |
|
| Mercury(I) |
Hg22+ |
Mercurous |
|
Anions>
| Formal Name |
Formula |
Alt. Name |
| Simple Anions |
| Arsenide |
As3− |
|
| Azide |
N3− |
|
| Bromide |
Br− |
|
| Chloride |
Cl− |
|
| Fluoride |
F− |
|
| Hydride |
H− |
|
| Iodide |
I− |
|
| Nitride |
N3− |
|
| Oxide |
O2− |
|
| Phosphide |
P3− |
|
| Sulfide |
S2− |
|
| Peroxide |
O22− |
|
| Oxoanions |
| Arsenate |
AsO43− |
|
| Arsenite |
AsO33− |
|
| Borate |
BO33− |
|
| Bromate |
BrO3− |
|
| Hypobromite |
BrO− |
|
| Carbonate |
CO32− |
|
| Hydrogen carbonate |
HCO3− |
Bicarbonate |
| Chlorate |
ClO3− |
|
| Perchlorate |
ClO4− |
|
| Chlorite |
ClO2− |
|
| Hypochlorite |
ClO− |
|
| Chromate |
CrO42− |
|
| Dichromate |
Cr2O72− |
|
| Iodate |
IO3− |
|
| Nitrate |
NO3− |
|
| Nitrite |
NO2− |
|
| Phosphate |
PO43− |
|
| Hydrogen phosphate |
HPO42− |
|
| Dihydrogen phosphate |
H2PO4− |
|
| Permanganate |
MnO4− |
|
| Phosphite |
PO33− |
|
| Sulfate |
SO42− |
|
| Thiosulfate |
S2O32− |
|
| Hydrogen sulfate |
HSO4− |
Bisulfate |
| Sulfite |
SO32− |
|
| Hydrogen sulfite |
HSO3− |
Bisulfite |
| Anions from Organic Acids |
| Acetate |
C2H3O2− |
|
| Formate |
HCO2− |
|
| Oxalate |
C2O42− |
|
| Hydrogen oxalate |
HC2O4− |
Bioxalate |
| Other Anions |
| Hydrogen sulfide |
HS− |
Bisulfide |
| Telluride |
Te2− |
|
| Amide |
NH2− |
|
| Cyanate |
OCN− |
|
| Thiocyanate |
SCN− |
|
| Cyanide |
CN− |
|
|
Further Information
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