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Introduction: What is Ionic Bonding?
Ionic bonds are a type of chemical bond formed when a cation (positively-charged ion) and an anion (negatively-charged ion) are electrostatically attracted.
This type of bonding typically occurs between atoms of very different electronegativities.
Lattice Structures
Unlike molecular structures, ionic compounds form lattice structures in their solid form, which are 3-dimensional arrangements of these ions.
Therefore, they do not exist as discrete units, and we instead use simplified ratios of cations to anions—called formula units—for calculations.
Lattice Energy
Lattice Energy: The amount of energy released during the formation of a mole of ionic solid from its gaseous constituent ions.
It is an effective way to measure the strength of ionic bonds, as higher lattice energies are associated with stronger intramolecular attraction.
Factors that determine bond strength within ionic compounds:
Charge: More charge per ion leads to stronger bonds, as there would be more attraction between opposite charges.
Example: MgO has stronger bonds than NaCl. Mg²⁺ is more positively-charged than Na⁺, while O²⁻ is more negatively charged than Cl⁻. The stronger polarization of MgO results in properties like higher melting points.
Radius: Smaller ionic radii leads to stronger bonds, as smaller ions have a higher charge density. Also, larger ions have more electron orbitals which leads to more repulsion, creating longer bonds.
Example: LiCl has stronger bonds than NaCl, because Li⁺ has a higher charge density than Na⁺.
Electronegativity: Higher polarity between
Charge is typically a more substantial factor of bond strength for ionic compounds.
How Ionic Bonds Form
Essentially, ionic bonds form from oppositely-charged ions interacting with each other.
An example of a physical process to form ionic bonds is to distill an aqueous solution, which removes the water from the system and leaves behind the ionic compound.
Chemical Process to Form Ionic Bonds:
A reduction-oxidation reaction occurs between electropositive (typically a metal) and electronegative (typically a nonmetal) atoms.
The metal loses one or more valence electrons (oxidized) → forms a cation.
The nonmetal gains those electrons (reduced) → forms an anion.
The ratio of cations to anions per formula unit depends on how much electrons they need to gain/lose in order to form a stable ion. The net charge for a formula unit must be zero.
Example: In NaCl, one Na⁺ balances one Cl⁻. In MgCl₂, one Mg²⁺ balances two Cl⁻ ions.
Once the ions are formed, they are attracted to each other via electrostatic forces as opposite charges attract.
Properties of Ionic Bonds/Compounds
Physical State: Forms crystal lattice structures of ions.
Polarity: Ionic bonds are very polar.
Solubility: Has relatively high solubility in polar solvents, where it can dissociate into ions.
Intramolecular Forces: Strong intramolecular forces due to electrostatic attraction between ions of opposite charges. Therefore, ionic compounds tend to have high melting points.
Electrical Conductivity:
As a liquid or in an aqueous state: Conductive due to freely-moving ions.
As a solid: Not conductive, as ions are locked in place.
Physical Property: Hard yet brittle, as shifting the ions' positions easily results in repulsion.
Calculating Lattice Energy
To be continued.
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