- Ionic bond
noble gaselectron configuration, and this electron enters the chlorine atom exothermically. The oppositely charged ions are then attracted to each other, and their bonding releases energy. The net transfer of energy is that energy leaves the atoms, so the reaction is able to take place.]
An ionic bond (or electrovalent bond) is a type of
chemical bondthat can often form between metaland non-metal ions (or polyatomic ionssuch as ammonium) through electrostaticattraction. In short, it is a bond formed by the attraction between two oppositely charged ions.
The metal donates one or more
electrons, forming a positively charged ion or cationwith a stable electron configuration. These electrons then enter the non metal, causing it to form a negatively charged ion or anionwhich 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 saltis sodium chloride. When sodium (Na) and chlorine (Cl) are combined, the sodiumatoms each lose an electron, forming a cation (Na+), and the chlorineatoms 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
electronegativityof 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 is not known to exist. All ionic compounds have a degree of
covalent bonding. The larger the difference in electronegativitybetween two atoms, the more ionic the bond. Ionic compounds conduct electricitywhen molten or in solution. They generally have a high melting pointand tend to be soluble in water.
Ions in crystal lattices of purely ionic compounds are spherical; however, if the positive ion is small and/or highly charged, it will distort the electron cloud of the negative ion, an effect summarised in Fajans' rules. This polarization of the negative ion leads to a build-up of extra charge density between the two nuclei, i.e., to partial covalency. Larger negative ions are more easily polarized, but the effect is usually only important when positive ions with charges of 3+ (e.g., Al3+) are involved. However, 2+ ions (Be2+) or even 1+ (Li+) show some polarizing power because their sizes are so small (e.g., LiI is ionic but has some covalent bonding present). Note that this is not the ionic polarizationeffect which refers to displacement of ions in the lattice due to the application of an electric field.
Ionic compounds in the solid state form three dimensional lattice structures, (see ionic crystal). The two principal factors in determining the form of the lattice are the relative charges of the ions and their relative sizes. Some structures are adopted by a number of compounds, for example the rock salt, sodium chloride, structure is adopted by many alkaline earth halides and binary oxides such as MgO.
trength of an ionic bond
"See main article
For a solid crystalline ionic compound the enthalpy change in forming the solid from gaseous ions is termed the
lattice energy.The experimental value for the lattice energycan be determined using the Born-Haber cycle. It can also be calculated using the Born-Landé equationas the sum of the electrostatic potential energy, calculated by summing interactions between cations and anions, and a short range repulsive potential energy term. The electrostatic potential can be expressed in terms of the inter-ionic separation and a constant ( Madelung constant) that takes account of the geometry of the crystal. The Born-Landé equationgives a reasonable fit to the lattice energy of e.g. sodium chloride where the calculated value is −756 kJ/mol which compares to −787 kJ/mol using the Born-Haber cycle. [David Arthur Johnson, "Metals and Chemical Change",Open University, Royal Society of Chemistry, 2002,ISBN 0854046658]
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 geometryaround each atom is determined by VSEPRrules, whereas, in ionic materials, the geometry follows maximum packing rules.
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 for the same reason i.e. that ions are free to move.
Some ionic compounds conduct electricity when solid, this is due to migration of ions under the influence of an electric field. (see
Fast ion conductor)
Substances in ionic form
Linear combination of atomic orbitals
* [http://dbhs.wvusd.k12.ca.us/webdocs/Bonding/Ionic-Bond.html Ionic bonding tutorial]
* [http://sciencehack.com/videos/view/xTx_DWboEVs Video on ionic bonding]
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Look at other dictionaries:
ionic bond — n. the chemical bond between two oppositely charged ions formed when one atom transfers electrons to another atom, as in the formation of sodium chloride; electrovalent bond: see COVALENT BOND … English World dictionary
ionic bond — ionic bond. См. электровалентная связь. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) … Молекулярная биология и генетика. Толковый словарь.
ionic bond — noun a chemical bond in which one atom loses an electron to form a positive ion and the other atom gains an electron to form a negative ion • Syn: ↑electrovalent bond, ↑electrostatic bond • Hypernyms: ↑chemical bond, ↑bond * * * noun Etymology … Useful english dictionary
ionic bond — Chem. the electrostatic bond between two ions formed through the transfer of one or more electrons. Also called electrovalence, electrovalent bond. [1935 40] * * * Electrostatic attraction between oppositely charged ions in a chemical compound.… … Universalium
ionic bond — UK / US noun [countable] Word forms ionic bond : singular ionic bond plural ionic bonds chemistry a chemical bond that is formed between two ions with opposite charges, when one or more electrons are passed from one atom to another See: covalent… … English dictionary
ionic bond — joninis ryšys statusas T sritis chemija apibrėžtis Elektrostatinis ryšys tarp priešjonių. atitikmenys: angl. ionic bond rus. ионная связь … Chemijos terminų aiškinamasis žodynas
ionic bond — a chemical bond in which electrons are transferred from one atom (e.g., sodium) to another (e.g., chlorine) so that one bears a positive and the other a negative charge, the attraction between these opposite charges forming the bond … Medical dictionary
ionic bond — ion′ic bond′ n. chem. the electrostatic bond between two ions formed through the transfer of one or more electrons • Etymology: 1935–40 … From formal English to slang
ionic bond — /aɪɒnɪk ˈbɒnd/ (say uyonik bond) noun Chemistry → electrovalent bond … Australian English dictionary
ionic bond — noun Date: 1939 a chemical bond formed between oppositely charged species because of their mutual electrostatic attraction … New Collegiate Dictionary