Glossary
Anion
A negatively charged ion formed when a neutral atom, typically a nonmetal, gains one or more electrons.
Example:
The fluoride anion (F-) is formed when a fluorine atom gains an electron, making it a common component in toothpaste.
Cation
A positively charged ion formed when a neutral atom, typically a metal, loses one or more electrons.
Example:
When a magnesium atom loses two electrons, it forms a Mg2+ cation, which is crucial for many biological processes.
Coulomb's Law
A law stating that the electrostatic force between two charged particles is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
Example:
Coulomb's Law predicts that a compound with +2 and -2 ions will have a much stronger attraction than one with +1 and -1 ions, assuming similar distances.
Crystal Lattice
A highly ordered, three-dimensional arrangement of ions in an ionic solid, maximizing attractive forces and minimizing repulsive forces.
Example:
The repeating cubic structure of sodium chloride's crystal lattice is why salt crystals are often cube-shaped.
Electrical Conductivity
The ability of a substance to conduct electricity; ionic compounds are poor conductors as solids but good conductors when molten or dissolved in water due to mobile ions.
Example:
Solid sodium chloride does not conduct electricity, but if you melt it or dissolve it in water, its mobile ions allow for excellent electrical conductivity.
Electrostatic Force
The attractive or repulsive force between electrically charged particles, which is the fundamental force holding ionic compounds together.
Example:
The powerful electrostatic force between a Ca2+ ion and an O2- ion in calcium oxide contributes to its extremely high melting point.
Hardness and Brittleness
Characteristic properties of ionic solids; they are hard due to strong forces resisting deformation but brittle because a slight shift can align like charges, causing repulsion and shattering.
Example:
If you hit a salt crystal with a hammer, its hardness and brittleness mean it won't dent but will instead shatter along planes of ions.
High Melting and Boiling Points
A characteristic property of ionic compounds due to the strong electrostatic forces within their crystal lattice, requiring significant energy to overcome.
Example:
Because of their high melting and boiling points, ionic compounds like salt remain solid even at very high temperatures, unlike many molecular compounds.
Ion Size
The radius of an ion, which is influenced by the number of electron shells and the nuclear charge; cations are smaller than their parent atoms, and anions are larger.
Example:
Understanding ion size helps explain why smaller Li+ ions fit more snugly into a lattice with F- than larger K+ ions, affecting properties like lattice energy.
Ionic Bond
A chemical bond formed by the complete transfer of valence electrons between atoms, resulting in oppositely charged ions that attract each other.
Example:
The strong attraction between K+ and Br- in potassium bromide is an ionic bond, holding the compound together.
Ionic Compound
A chemical compound formed by the electrostatic attraction between oppositely charged ions, typically a metal cation and a nonmetal anion.
Example:
Table salt, sodium chloride (NaCl), is a classic example of an ionic compound where Na+ and Cl- ions are held together.
Lattice Energy
The energy released when gaseous ions combine to form one mole of an ionic solid, serving as a measure of the strength of the ionic bonds within the crystal lattice.
Example:
The high lattice energy of magnesium oxide (MgO) means it takes a tremendous amount of energy to break apart its ionic bonds, leading to its very high melting point.