An ionic bond results from the transfer of an electron from a metal atom to a non-metal atom.
Ionic bonds are formed between cations and anions.
A cation is formed when a metal ion loses a valence electron while an anion is formed when a non-metal gains a valence electron. They both achieve a more stable electronic configuration through this exchange.
Ionic solids form crystalline lattices, or repeating patterns of atoms, with high melting points, and are typically soluble in water.
Cations and Anions
Ionic bonds involve a cation and an anion. The bond is formed when an atom, typically a metal, loses an electron or electrons, and becomes a positive ion, or cation. Another atom, typically a non-metal, is able to acquire the electron(s) to become a negative ion, or anion.
One example of an ionic bond is the formation of sodium fluoride, NaF, from a sodium atom and a fluorine atom. In this reaction, the sodium atom loses its single valence electron to the fluorine atom, which has just enough space to accept it. The ions produced are oppositely charged and are attracted to one another due to electrostatic forces.
At the macroscopic scale, ionic compounds form lattices, are crystalline solids under normal conditions, and have high melting points. Most of these solids are soluble in H2O and conduct electricity when dissolved. The ability to conduct electricity in solution is why these substances are called electrolytes. Table salt, NaCl, is a good example of this type of compound.
Ionic bonds differ from covalent bonds. Both types result in the stable electronic states associated with the noble gases. However, in covalent bonds, the electrons are shared between the two atoms. All ionic bonds have some covalent character, but the larger the difference in electronegativity between the two atoms, the greater the ionic character of the interaction.
Ionic Compounds
An ionic bond is formed through the transfer of one or more valence electrons, typically from a metal to a non-metal, which produces a cation and an anion that are bound together by an attractive electrostatic force. On a macroscopic scale, ionic compounds, such as sodium chloride (NaCl), form a crystalline lattice and are solids at normal temperatures and pressures.
Crystalline Lattice: Sodium chloride crystal lattice
The charge on the cations and anions is determined by the number of electrons required to achieve stable noble gas electronic configurations. The ionic composition is then defined by the requirement that the resulting compound be electrically neutral overall.
For example, to combine magnesium (Mg) and bromine (Br) to get an ionic compound, we first note the electronic configurations of these atoms (valence level in indicated in italics):
Mg: 1s22s22p63s2
Br: 1s22s22p63s23p63d104s24p5
In order to achieve noble gas configurations, the magnesium atom needs to lose its two valence electrons, while the bromine atom, which has 7 valence electrons, requires one additional electron to fill its outer shell. Therefore, for the resulting compound to be neutral, two bromine anions must combine with one magnesium cation to form magnesium bromide (MgBr2). In addition, though any ratio of 2 bromine atoms to 1 magnesium atom will satisfy the two requirements above, the formula for ionic compounds is typically presented as the empirical formula, or the simplest whole-number ratio of atoms with positive integers.
Note that the cation always precedes the anion both in written form and in formulas. In the written form, while the cation name is generally the same as the element, the suffix of single-atom anions is changed to –ide, as in the case of sodium chloride. If the anion is a polyatomic ion, its suffix can vary, but is typically either –ate or –ite,as in the cases of sodium phosphate and calcium nitrite, depending on the identity of the ion.
More examples:
lithium fluoride: Li+ and F– combine to form LiF,calcium chloride: Ca2+ and Cl– combine to form CaCl2
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