An ionic bond is an electrostatic force that holds atoms together through electron transference. Chemical compounds held together with ionic bonds separate in solution to form individual ions.
In their most stable configuration, the outer electron shells of an atom are evenly filled. If there are too many or too few electrons to evenly fill these shells, the atom will tend to lose or gain electrons to reach a lower energy state which is more stable. An atom's tendency to gain or lose electrons is measured by its electronegativity. A high electronegativity value means the atom tends to hold on to its electrons, while a low value means the atom is electropositive and tends to give them up. Electronegative and electropositive atoms can combine to form stable molecules. The magnitude of the difference between their electronegativity values determines the type of bond the atoms will form. If the difference is low, the atoms tend to share electrons more equally and form covalent bonds. If the difference is large (greater than 1.7 units), the atoms will form ionic bonds because some of the atoms will donate electrons and other atoms will receive electrons.
Inorganic compounds, such as salts, are held together by ionic bonds. In simple compounds, the electric charge is easily spread across the composite atoms. In more complex solids, the atoms form three-dimensional configurations in which anions might be shared by several adjacent cations. This leads to a network of closely packed atoms held together by powerful electric forces. Therefore, ionic solids tend to be strong, crystalline materials with definite patterns of cleavage and high melting points.
When ionic compounds are dissolved in water, they separate into their component ions. This separation process is called ionization. For example, when sodium chloride (NaCl), also known as table salt, is dissolved in water, it ionizes to release positive sodium ions (Na+) and negative chloride ions (Cl-). These ions allow the solution to conduct electricity. Therefore, ionic compounds are also called electrolytes. Covalent compounds like sugar are non-conductive and are called non-electrolytes.
When solutions of different ions are mixed, chemical reactions may take place. Different combinations of ions can come together to form more stable compounds that are not soluble in water. These compounds are called precipitates because they fall out of solution. For example, when silver nitrate (AgNO3) and sodium chloride (NaCl) are dissolved in water, four ions are formed: Ag+, NO3-, Na+ and Cl- . Because of their relative electronegativities, the silver ions and the chloride ions will bond together to form solid silver chloride (AgCl) which is not soluble in water.
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