EXAM 4 STUDY GUIDE
Unit 3 Module 3 Key Concepts
Ionic Species- Formed between metals(mostly 1A and 2A columns) and nonmetals ● Nonmetals have super high electronegativities compared to metals
○ The differences between the electronegativities are >2.0 so the bonds are ionic and not covalent
● Because of this, complete electron transfer occurs and the metals lose an electron to the nonmetal.
○ This results in a much much stronger bond than covalent bonds (ionic bonds>covalent bonds> IMF’s)
○ There is a localized charge between the metal and nonmetal:
○ The metals that lose an electron become positively charged (cations) ○ The nonmetals that gain an electron become negatively charged (anions) ○ They then form lattice structures
● The Common ions that form depend on column of the periodic table:
(only aluminum in this class)
Transition Metals If you want to learn more check out Are tissues groups of cells of the same type?
● Form a variety of charges so usually given to you by metal(number). For example: Cu(I) is the Copper ion with a +1 charge (remember metals form positively charged ions)
● When anions and cations combine to form molecules, they combine in a way so that the overall charge of the molecule is neutral or 0.
○ Therefore, when creating a molecular equation using an anion and cation, we first look at common ions and add subscripts so that the charges in the end are balanced.
○ Quick Rule: the charge number of the species will be the subscript of the other species Don't forget about the age old question of What happens to kinetic energy when an object slows down?
■ 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.
● The specific regions of electrons have specific charges
○ In covalent molecules, the electrons are delocalized in the molecule
● However, in a molten state, the electrons are able to move around and conduct electricity ○ Solid- does not conduct electricity We also discuss several other topics like Who is william herschel?
○ Liquid- conducts electricity
Properties of Ionic Compounds
● Ionic Compounds>Covalent Compounds = Ionic has higher boiling points than covalent. Forces = Coulomb’s Law:
q q1 2
And we use it to predict boiling points: If you want to learn more check out Isaac had two sons; who are they?
Higher boiling points caused by:
● Larger charge of the ions (larger q1,q2)
○ Always look at this factor first
○ Check by multiplying absolute values of q1 and q2
■ i.e (+2*-2) < (+3*-3) so (+3*-3) molecule is expected to have a higher boiling point.
○ Higher charge= stronger bonds= higher boiling point
● Smaller the size of the ions: r is radius
○ 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 We also discuss several other topics like What is the demand curve?
○ Cations- radius of the atom becomes smaller when lose electron
○ Anions- radius of the atom becomes larger when gain electron
● 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. If you want to learn more check out What is the treatment for pulmonary?
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
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. 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: OH−
Carbonate ion: CO32−
Phosphate ion: PO43−
*Nitrate ion: NO3−
*Sulfate ion: SO42−
*Important for CHEM 121 and 122
Unit 4 Module 1 Key Concepts
Chemical reactions involve reactants that combine and rearrange to form products. Mass is conserved in these reactions
In the reactions, there is a net transfer of energy:
● Endothermic- Energy is absorbed/put in from the environment
● Exothermic- Energy is released into the environment
● Reactions occur in definite proportions, in moles.
● Stoichiometric Coefficients represent the number of moles of each reactant that react with each other to form a specific number of moles of products.
● The stoichiometric coefficients need to satisfy the equation: mass is conserved so however many of each atom type you start with on reactant side, you need to end with on the product side.
● It takes energy to break bonds (energy has to be added) and energy is released when bonds are formed
● If reactants have lower potential energy than products- have to break bonds to get to higher potential energy- add energy = endothermic reaction
● If reactants have higher potential energy than products- have to form bonds to get to lower potential energy- energy is released from the system = exothermic reaction ● Change in energy from Reactants to Products is represented on an reaction energy coordinate diagram.
● In order to form products, the reactants must collide
○ The collisions must be in the proper orientation for the proper products to form ○ Collisions are more effective when:
■ There are less molecules/reactants that need to collide = reactions are
● When comparing collision effectiveness always look at the number
needed to collide first. If the same number look at:
■ How complex the molecules are. Less complex= higher collision
effectiveness. = reactions are faster
○ More effective collisions= reactions are faster
● The molecules must collide with enough energy for the reactions to occur. ○ Minimum energy required is called Activation Energy (Ea)
○ Lower Ea means reaction is faster
○ Can lower Ea needed with a catalyst only
○ The Ea is found by the difference between the potential energy of transition state and the potential energy of the starting reactants. (starting point of reactant and the peak on the diagram)
● Can change speed of reactions by changing other factors
● Increase Temperature= more collisions, reaction will be faster
● Increase Pressure= more collisions, reaction will be faster
● Decrease Volume= less room- more collisions, reaction will be faster ● Increase Concentration= more collisions, reaction will be faster
● Can be reversible or irreversible
○ Reversible- products can combine to reform reactants
○ Irreversible- products cannot reform reactants
● Reactions have “stopped” when the concentration of products to reactants stop changing with time
○ Called Chemical Equilibrium where the forward and backward processes are occurring at the same rate
● Reactions are Reactant Favored or Product Favored
○ Reactant Favored- at the end, higher concentration of reactants than product ■ Endothermic reactions are reactant favored
○ Product Favored- at the end, higher concentration of products than reactants. ■ Exothermic reactions are product favored
● Reactions are favored by Ea or configuration effectiveness or both
○ Ea (Activation Energy)- whichever one has the lower Ea is favored
○ Configuration Effectiveness- see above: collision model- more effective is favored
Unit 4 Module 2 Key Concepts
1. Start with grams of reactants (given) and convert to moles of reactants a. Grams to moles
2. Then consider balanced chemical equation and stoichiometric coefficients a. Transform moles of reactant to moles of product
3. Then finally use the molar mass to find grams of products.
a. Transform moles of product to grams of product
4. Can solve in reverse
5. For questions where we have to determine the limiting reactant:
a. Given: grams of each reactant
b. Convert the grams of reactants to moles
c. Put it in a ratio comparing the moles of one reactant to the other
d. Then compare that ratio to the ratio of the stoichiometric coefficients of the balanced chemical equation
e. In this process, you are comparing the moles of “how much they give you” to the moles of “the balanced chemical equation” in order to determine which of the reactants is limiting
f. If the ratio of given is smaller than balanced, the reactant on top is the limiting reactant
g. If the ratio of given is larger than balanced, the reactant on the bottom is the limiting reactant