ionic bonding
Post on 09-Feb-2016
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Ionic Bonding
• Metal atoms with low ionization energies and non-metal atoms with high electron affinity form cations (+) and anions (-)
• Oppositely charged ions attract to a crystalline structure
Ionic Bonding
Coulomb’s Law
The energy of interaction between the pair of ions can be calculated
Where Q1 and Q2 are the charges of the ions and r the distance between the ion’s centers
Since one charge is always + and the other -, the energy will be a negative number
The ion pair has lower energy than separate ions
1 2QQEnergy kr
1 2QQEnergy kr
Lattice Energy
Quantity of energy required for 1 mole of the solid ionic substance to be separated into its ions
Higher the negative value (exothermic) the more stable the compound
The higher the lattice energy of an ionic compound the harder, more brittle, and the higher the melting, boiling and vaporization points
Crystal Lattice Strength
Based on Coulomb’s Law, we expect that ionic solids formed by smaller atoms or by atoms that have greater charge, will be stronger
Example:Why is the lattice energy for MgO about four times greater than the lattice energy form NaF?
• Which substance would have a higher melting point : NaF or CsI?
• Which would have a higher lattice energy: FeO or Fe2O3?
Ionic Structures
Can have many types of arrangements Arrangement depends on the charge and size
of the ions involved
Forming The Ions
The ions are formed when electrons are transferred from the atom with low electronegativity to an atom with high electronegativity
Predict the compound formed between aluminum and fluorine.
Sizes of Ions
Cations are smaller than their parents Anions are larger than their parents Ions of the same charge, size increases going
down a group List the following in order of decreasing size
Mg2+, Ca2+, Ca
Isoelectric Series
Comparitive sizes of ions all possessing the same number of electrons
As nuclear charge increases, the radius decreases
O2- > F- > Na+ > Mg2+ > Al3+
Example
Arrange the ions S2- , K+ , Ca2+, and Cl- in order of decreasing size.
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