U3 M3: Characterizing Ionic Networks
How do we predict properties of ionic compounds
Forms between Metals and nonmetals (mostly in the 1A and 2A columns)
● Nonmetals have relatively higher electronegativities compared to metals
● If differences between electronegativities is above or equal to 2.0 we consider the bonds not to be polar covalent bond but an ionic bond
● Electron Transfer- Instead of a polar covalent bond, the huge differences in electronegativities cause the metals to completely transfer their electrons to nonmetals creating an ionic bond. ○ Forms a localized charge between the metal and nonmetal
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■ Metals form positive charge and nonmetals form negative
○ Metals have low ionization energy- easy to give up electron to complete octet ○ Nonmetals have high ionization energy- easier to take electron to complete octet ● Cation/cationic species- positive charge: metals that give up electron
● Anion/anionic species- negative charge: Nonmetals that take the electron
● Ionic bonds are much stronger than Covalent bonds.
● Ionic molecules form into crystalline networks or lattice structures.
Common Ions that form:
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(only aluminum in this class)
More difficult to predict ion charges because they form a variety of charges
● Therefore usually given
Use charges by the name of transition metals: positive values of roman numerals ● I.e. Cu(I) means Copper with positive 1 ion charge
When forming an ionic molecule, cations and anions form to produce an overall neutral charge ● Want to consider the stable charges of both atoms (what ions do they form): then balance the charges of the entire molecule if they were to react so that the entire molecule has a 0 charge ○ In other words, when forming a molecule between an anion and a cation, we make sure we have the right number of cations and anions so that when combined, the overall charge is 0. We also discuss several other topics like How is a mass shooting defined?
● Quick Rule: the charge number of the species will be the subscript of the other species ○ I.e if one atom has a +2 charge and the other has a -3 charge, then to balance the molecule you need 3 of the first atom and 2 of the other atom.
Electrons are localized meaning they don’t move
● Specific regions have specific charges
● As opposed to covalent molecules which have delocalized electrons
However, in a molten state, ions can move freely and establish an electric current ● Ionic species in solid state- doesn’t conduct electricity If you want to learn more check out The study of human origins is known as what?
● Ionic species in fluid state- conducts electricity
Properties of Ionic Compounds
Properties of ionic compounds are determined by charge and size of ions in the network. Stronger than any covalent bond because ion-ion interactions are super strong.
● Ionic bonds are always stronger than covalent bonds
○ Can think of ionic bonds as both bonds and intermolecular forces
● Same as before: stronger the bonds, higher the boiling points
Forces are determined by Coulomb’s Law:
And we use it to predict boiling points:
The following all lead to a stronger force which leads to higher boiling points:
● Larger charge of the ions (larger q1,q2)
○ Always look at this factor first before looking at size.
○ Check by multiplying absolute values of q1 and q2 to get the total charge.
○ If one molecule has a larger charge than another, that means it has stronger bonds and a higher boiling point
■ Higher charge= stronger bonds= higher boiling point If you want to learn more check out It is the principle that a law isn’t broken until an illegal act has been committed. what is it?
● Smaller the size of the ions (r2):
○ If the charges when multiplied are the same when comparing molecules, then look at the size of the atoms
■ Smaller atoms have a stronger bond and higher boiling point therefore:
■ Smaller radius=stronger bonds= higher boiling point
○ Cations- when metal loses an electron to nonmetal, the radius of the atom becomes smaller
○ Anions- when nonmetal gains an electron from nonmetal, the radius of the atom becomes larger Don't forget about the age old question of How to be a predator?
● Ionic compounds that are insoluble in water are composed of ions with strong interactions between each other (large charge and small radius)
● Dissolved ionic compounds are called electrolytes
○ Strong electrolyte- readily conducts electricity meaning it dissolves easily in solution ○ Weak electrolyte- solutions of slightly soluble ionic compounds barely conduct electricity and don’t dissolve easily
When looking at PEC Diagrams: we look at mixed and unmixed states between ionic compounds and water.
For an ionic compound to be soluble in water, at least one of these has to be true: 1. Net interactions between ions and water molecules should be stronger than the net interactions between ions themselves (leads to lower potential energy)
a. In other words, the interactions between ions and water are stronger than interactions between ions- this leads to high solubility in water.
2. Number of configurations that ion and water molecules can adopt when mixed is larger than total number of configurations they can have if they don’t mix
CANNOT NEGLECT THE INTERACTIONS WATER HAS WITH IONIC COMPOUNDS WHEN INTERPRETING PEC DIAGRAMS
As we input more ions into system (water) because of ion-dipole interactions (between the ions and polarity of water), there will, many times, be less configurations available because of the way the water molecules will arrange itself around the ions
● I.e. NaCl not strong enough to overcome water intermolecular forces so it is soluble
RULE OF 4
1. If the absolute value of the product of charges is less than 4, it is soluble.
a. On exams this rule always applies
b. Sapling doesn’t always work because there are some exceptions to this rule 2. If greater than or equal to 4, then it is insoluble.
3. Doesn’t matter how many ions there are just multiply the charge values of one of each atom. 4. In other words, if the product of the absolute values of the charges is less than 4, then the ion-ion interactions are not enough to overcome the interactions between the ion and the water. This will lead to the ionic compound being soluble.
Ionic compounds in which ions in the lattice are not atomic (one single ion) but molecular (several covalently bonded ions)
Hydroxide ion: ��������−
Carbonate ion: ��������32−
Phosphate ion: ��������43−
Ammonium ion: ��������4+
*Nitrate ion: ��������3−
*Sulfate ion: ��������42−
*Important for CHEM 121 and 122
There are always one anion and one cation that combine in an ionic compound. However, one or both may be molecular or a polyatomic ion.