Chem-Bonding and Intermolecular Forces;thermodynamics

What is the bond angle of sp3?

109

What is the bond angle of sp2

120

What is the bond angle of sp?

180

How many electrons are found in π bonds in acetylene (C2H2)?

4

Among the following, which molecular geometry CANNOT result in a nonpolar structure? Question 12 Answer Choices A. Bent B. Diatomic covalent C. Square planar D. Trigonal planar

A

Gibbs free energy equation

ΔG = ΔH - TΔS Getting High Test Score T is always in Kelvin, Kelvin is always positive temperature

endothermic

- positive delta H -Requiring energy -breaking bond

Ion-dipole forces

-IMF -Ion-dipole forces are produced between ions and polar molecules (charge and delta charge) -the larger the ionic charge and the larger the dipole the larger the force -a more highly charged ion generates a stronger force -a more polar molecule generates a stronger force

Hess's law

-Reversing the direction of a reaction changes the sign of delta H. ex. if A-->B has delta H, then B-->A has -delta H -changing the stoichiometric coefficients of a reaction means you must scale the value of delta H for the reaction. Ex. A-->B has delta H, then 2A-->2B has 2xdelta H -Add reactions together to cancel out intermediate species

Entropy

-S -randomness, disorder, microstates -increases the number of particles increases entropy -changing phase from solid to liquid to gas increases entropy -increasing the temperature increases entropy

Calculate delta H

-bonds broken + bonds formed -enthalpy of formation: product-reactant -Hess's law of heat summation

Coordinate covalent bonds

-coordinate covalent bonds are formed between atoms with lone pairs and electron deficient species -The electrons are localized directly b/w the atoms -electrons are donated from the nucleophile (ligand), some ligands may donate more than one lone pair of electrons -compounds with coordinate covalent bonds are easily dissociated (coordinate complexes)

Covalent bonds

-covalent bonds are formed between atoms with high electronegativity (nonmetals with nonmetals) -The electrons are localized directly between the atoms, so not able to conduct electricity -The electrons in the bond are donated from both atoms -compounds with covalent bonds are insulators and rigid -The molecular dipole is found by adding all the bonds dipole -A non-polar molecule can be formed with polar bonds that cancel each other

Gibbs Free Energy

-delta G -energy available to do work -spontaneous process is negative delta G (exergonic) -non-spontaneous process is positive delta G (endergonic)

London dispersion forces

-induced dipole-induced dipole forces ex. Cl-Cl and Cl-Cl -the force is produced by collisions that produced temporary but small dipoles by deforming the electron cloud -a molecule with more electrons and larger size generates a stronger force (more polarizable) -ex. F2<Cl2<Br2<I2 -Dispersion forces are very weak and easily cleaved

Intermolecular forces

-intermolecular attractions are produced when particles of opposite charge attract each other +/- > delta +/delta ->slight charge -the strength of an IMF is dependent upon: -larger charges=stronger attractive force -particle size is negligible due to large distances -Stronger IMF=particles held together more tightly -pulling apart the particles is always endothermic

ionic bond

-ionic bonds are formed between particles of opposite charges (cations with anions) -the electrons are localized on the ion (not conductive) -The ions dissociate in aqueous solution as an electrolyte, an aqueous solution of an ionic compound is a conductor. The compound itself with ionic bonds are insulators and brittle

Metallic bonds

-metallic bonds are formed between atoms with low electronegativity (metals with metals) -The valence electrons are delocalized among all the atoms, they are free-floating everywhere, the nucleus and core electrons are in place. -The electrons in the bond are donated from all the atoms, known as the 'sea of electrons.' -compounds with metallic bonds are conductors and malleable

strength of a chemical bond is dependent upon

-more electrons shared=stronger bond -shorter distance between atoms=stronger bonds

exothermic

-negative delta H -releasing energy -forming bond

Dipole-induced dipole forces

-produced between polar and nonpolar molecules -the force is generated when a polar molecule attracts/repels electron density in a nonpolar molecule -a more polar molecule generates a stronger force -a molecule with more electrons and larger size generates a stronger force (more polarizable) -dipole-induced dipole forces are very easily cleaved

dipole-dipole forces

-produced between polar molecules -The force is aligned along the permanent molecular dipole, a more polar molecule generates a stronger force -dipole forces are easily cleaves

Hydrogen bonding

-produced between very polar molecules -the force is aligned along the permanent BOND dipole -more paired donors and acceptors generate a stronger force -H bond with F,O,N

Enthalpies of formation

-the amount of energy associated with forming one mole of a compound from its constitutive elements in their standard states -the enthalpy of formation of any element in its standard state is defined as 0 ex. Br2(l), O2 (g), Na(s), Hg(l)=0 -Product-reactant

Which of the following lists hydrogen halides in terms of increasing standard heats of formation? Question 8 Answer Choices A. HF < HCl < HBr < HI B. HI < HBr < HCl < HF C. HBr < HF < HCl < HI D. HF < HI < HCl < HBr

A The general formula for hydrogen halide formation is: . The reaction that forms the most stable HX will be the most exothermic and have the most negative standard heat of formation. Fluorine is the smallest, most electronegative halogen and forms the only hydrogen halide of the group that is not a strong acid. HF is the most stable hydrogen halide and will have the most negative heat of formation. This eliminates choices without HF having the lowest heat of formation. Indeed, the heat of formation of HI is actually endothermic. This eliminates choice HF < HI < HCl < HBr.

Which of the following molecules has the lowest boiling point? Question 7 Answer Choices A. F2 B. Cl2 C. H2O D. HCN

A Boiling point questions are really an intermolecular forces question in disguise. Because the question is asking for the lowest boiling point, it is really asking which of the choices has the weakest intermolecular forces. Remember that the order from the strongest to weakest intermolecular force is: hydrogen bonding > dipole-dipole forces > London dispersion forces. H2O (water) can hydrogen bond, HCN has dipole-dipole forces, and F2 and Cl2 only have London dispersion forces. Thus, H2O and HCN may immediately be eliminated. To differentiate the two molecules that solely exhibit London dispersion forces, the Cl2 with a larger molecular weight will have the stronger force because it is more polarizable and has a larger surface area of interaction. Thus, F2 will have the lowest boiling point among the choices.

The ferrous ion fits snugly inside protoporphyrin's "donut hole". Among the following four, identify the ion that cannot form a protoporphyrin-metal complex due to excessive size. Question 2 Answer Choices A. K+ B. Fe3+ C. Cu2+ D. Mg2+

A If the ferrous ion fits snugly into the porphyrin's donut hole, then larger ions will not fit inside and form stable complexes. Based upon the periodic trend of sizes of neutral atoms, atomic size increases as one moves down or to the left in the periodic table. However, there is a second consideration: For each electron an atom loses, its size contracts. So we can say that the ion with the least positive charge, and the furthest to the left and bottom of the periodic table, should be the largest. Potassium ion must be the largest.

What is the vapor pressure of a gas compared to atm pressure?

It must be greater than atm pressure

Ammonium chloride is also formed when bleach and ammonia are mixed together. What is the phase of pure ammonium chloride at room temperature? Question 3 Answer Choices A. Solid B. Liquid C. Gas D. Plasma

A. Ammonium chloride, NH4Cl, is an ionic compound, and at room temperature, all ionic compounds are solids.

Is forming bonds endothermic or exothermic?

exothermic

When drawing Lewis structures, how do we arrange the atoms?

Arrange the atoms with the least electronegative atom in the center. -there is only one central atom -carbon always goes in the center -Hydrogen never goes in the center, only makes one bond

How many electrons are shared in the bond between sodium and chlorine in a molecule of NaCl? Question 13 Answer Choices A. 1 B. 0 C. 2 D. 3

B NaCl is an ionic compound, and no electrons are shared in an ionic bond.

How many orbitals make up the 5f subshell? Question 12 Answer Choices A. 10 B. 7 C. 5 D. 14

B There is one s orbital, and there are three p orbitals, five d orbitals, and seven f orbitals. Thus, the answer is 7. (Note: Do not confuse the number of orbitals in a subshell with the number of electrons the subshell can hold. Each orbital can hold two electrons, so the capacity of an nf subshell is 7 × 2 = 14 electrons.)

What is responsible for holding together the long, aliphatic hydrocarbon chains in the bilayer? Question 1 Answer Choices A. Hydrophobic force B. Hydrophilic force C. van der Waals forces D. Both A and C

C. There is no such thing as the hydrophobic (choices A and D can be eliminated) or hydrophilic force (choice B can be eliminated). Nonpolar molecules interact via van der Waals forces, and polar molecules interact through dipole and van der Waals forces, although the later is very weak compared to the former and therefore usually ignored.

In which of the following does hydrogen have a partial negative charge? Question 3 Answer Choices A. H2O B. NH3 C. BH3 D. CH4

C

In a mixture of SnCl4, GeCl4, and SiCl4, which one would be the first to be isolated by fractional distillation? Question 3 Answer Choices A. SnCl4 B. GeCl4 C. SiCl4 D. The order of isolation is random, so any of the three compounds could be isolated first.

C Fractional distillation, as implied by the passage, separates components of a mixture based on their volatility. Upon heating the mixture, the most volatile component is expected to be isolated first. The three molecules given in the question all have the same geometry and a zero net dipole moment (thus experiencing only London dispersion forces), so we use their molecular weights to predict their relative boiling points. As we are looking for the first compound isolated, choice B can be eliminated as it is in the middle of choices A and C on the periodic table. Since SiCl4 has the lowest molecular weight of the three, it should have the lowest boiling point, and thus be isolated first in a fractional distillation of a mixture of these compounds.

How many hybrid orbitals does each fluorine atom in XeF4 have? Question 8 Answer Choices A. Five B. Six C. Four D. Seven

C. Each fluorine atom has three lone pairs and a single bond, giving a total of four electron groups. These require four orbitals: one s and three p to make four sp3 orbitals.

What is the oxidation state of the phosphorus atom in a phospholipid? Question 5 Answer Choices A. +3 B. +4 C. +5 D. +6

C. Since the question refers to an organic molecule, the quickest way to determine the oxidation state of any atom is to count the number of bonds that atom has with a more electronegative atom, and then from this number, subtract the number of bonds the atom has with a less electronegative atom. In the case of phosphorus, this would give a 5 - 0 = +5 oxidation state

stronger bonds have higher or lower bond dissociation energy

higher

Which one of the following transition metal oxides is NOT colored? Question 3 Answer Choices A. CuO B. FeO C. TiO2 D. Mn2O3

C. In order to find the white (no color) compound, we have to find the metal ion with ten d electrons or with no d electrons. Note the electronic configurations for the following metal ions: Cu(II): [Ar] 3d9 (colored blue) Fe(II): [Ar] 3d6 (colored pale green) Ti(IV): [Ar] (white, no color) Mn(III): [Ar] 3d4 (colored pale pink) So the correct answer is choice C, TiO2. (Titanium dioxide is used as a white paint pigment; it is very likely that your walls at home are covered with titanium dioxide.)

Alkenes can form s bonds with metal centers through donation of p electrons to empty orbitals on the metal, usually drawn as shown below for a generic metal (M) bound to n generic ligands (L). Compared to the C=C bond length in an unbound alkene, the C=C bond length in such a metallated alkene will be: Question 4 Answer Choices A. unaffected. B. longer or shorter depending on the metal. C. shorter. D. longer.

D The fact that C=C bonds are shorter than C—C bonds is due to the shared electrons in the π bond. If these electrons participate in a bonding interaction with the metal, they are less centralized between the two carbons. Therefore, the bond between the carbons will have less double bond character, and be longer. Any metal which accepts such a bond will cause its lengthening.

Perspiration is important in maintaining normal body temperature. Compared to water at its boiling point, which of the following is true about water at normal human body temperature? Question 7 Answer Choices A. Intermolecular forces are weaker B. Average kinetic energy is greater C. More energy is required for gas expansion D. The heat required for vaporization is higher

D As water on the skin vaporizes it absorbs energy and cools the body. Temperature is a measure of average kinetic energy, so water has less average kinetic energy at 37°C compared to 100°C. As temperature increases, water requires more and more energy to expand the volume of its gaseous phase. Although the elimination of "more energy is required for gas expansion" might not be obvious, "the heat required for vaporization is higher" is a better answer. Water is much more likely to vaporize at its boiling point than at body temperature. It takes additional energy to go from the liquid to gas phase at lower temperatures. Therefore the heat required to vaporize is higher when water is at lower temperatures.

How many of which type of orbitals are used to create the hybrid orbitals on carbon in a molecule of ethylene (C2H4)? Question 6 Answer Choices A. One s and one p orbital B. Two s and two p orbitals C. One s and three p orbitals D. One s and two p orbitals

D Since there are three electron groups around each trigonal planar carbon atom, a total of three hybrid orbitals (sp2) are needed. Therefore one s and two p atomic orbitals are required to form these hybrids.

Which of the following compounds displays the lowest vapor pressure at 15˚C? Question 10 Answer Choices A. NH3 B. CO2 C. SO2 D. HF

D The compound with the least vapor pressure has the strongest intermolecular forces. Both NH3 and HF can form hydrogen bonds, the strongest type of intermolecular force, so one of these compounds is the most likely correct answer. The polarity of the H?F bond is much greater than that of an H?N bond and HF has a greater molecular weight, both of which result in HF having the lowest vapor pressure of the compounds listed. Carbon dioxide is nonpolar, so it would only have weak London dispersion forces making it a gas at 15°C (CO2 is wrong). Sulfur dioxide is a polar compound and would experience both dipole-dipole interactions and moderate London dispersion forces as it has a relatively large molecular weight. These forces are weaker than the hydrogen bonds in HF, so SO2 is wrong. While this question asks for the lowest vapor pressure rather than to rank all four compounds based on this property, it's good to note that the boiling point of SO2 is higher than the boiling point of NH3 due to the larger molecular weight of SO2.

Polar or non-polar

If electronegativity difference is zero or very small, the bond is non-polar, and electrons are shared equally If electronegativity difference is greater than 0 and moderate in value, the bond is polar, and electrons are NOT shared equally

Which of the following correctly describes the order of bond strengths among the following phosphorous halides? Question 4 Answer Choices A. P-Br > P-Cl > P-F B. P-Br > P-F > P-Cl C. P-Cl > P-F > P-Br D. P-F > P-Cl > P-Br

D.For this ranking question, first eliminate choices B and C since Cl is in between F and Br on the periodic table and should be in the middle of the ranked bonds. From the data given in Table 1, it can be seen that the enthalpy of formation becomes increasingly negative going from P-Br to P-Cl to P-F. This indicates that fluorine forms the strongest bond, and bromine the weakest (choice D is correct).

Enthalpy

Energy stored within chemical bonds or any attractive force

diatomic molecules in standard states

H O N Cl Br(l) I(s) F

Hemoglobin

Hemoglobin is a tetramer, meaning it consists of four individual protein chains clumped together. Each hemoglobin unit has one iron-oxygen binding site, so each hemoglobin macroprotein has four iron-oxygen binding sites

Change in enthalpy

The change in enthalpy of a reaction is the difference between what is stored in the reactants vs. the products.

Is enthalpy a state function?

Yes, enthalpy is a state function, it's independent of pathway. This is the same for all thermo quantities

what is considered to be a good ligand?

a good ligand has excess electron density, such as lone pairs

AX2E2

bent

When a sample of solid NH4NO3 is dissolved in water, the reaction flask becomes cold to the touch. What can be concluded about the given thermodynamic values for the solvation process? Question 3 Answer Choices A. ΔG < 0, ΔH < 0, ΔS > 0 B. ΔG > 0, ΔH < 0, ΔS > 0 C. ΔG < 0, ΔH > 0, ΔS > 0 D. ΔG < 0, ΔH > 0, ΔS < 0

c Since the solvation process is observed to occur, it is spontaneous, so ΔG < 0. If the reaction flask is cold to the touch, then the enthalpy change of solvation is positive (ΔH > 0) as this is an endothermic process. Finally, dissolving a solid in a liquid tremendously increases the disorder of the two components as they mix, so ΔS > 0.

what bond does hemoglobin form?

coordinate covalent bond

Sodium dodecyl sulfate, also known as SDS, is a common denaturation agent used while separating proteins via gel electrophoresis. It is composed of a highly charged head and a long hydrocarbon tail. Given application of SDS to a protein increases its solubility in water, what forces are responsible for association of SDS with the protein of interest? Question 9 Answer Choices A. Dipole-dipole forces B. Hydrogen bonding C. Ion-dipole forces D. London dispersion forces

d. Given the association of SDS with the protein increases its solubility in water, the highly charged head is likely to interact with water surrounding the protein while the hydrophobic tail interacts with the protein itself. Of the intermolecular forces listed, London dispersion forces predominate in nonpolar molecules and are responsible for the association of SDS with the protein (London dispersion forces is correct). The other types of forces require the attraction of full or partial charges on the associating molecules. If the charged heads of SDS were associated with the protein, the nonpolar tails would be forced to interact with the aqueous environment and would decrease the solubility of the protein instead.

Ionic or covalent bond

determined by the difference in electronegativity of the atoms -If electronegativity difference is small, it's covalent, typically between non-metals -Ionic bonds break to form ions

Is breaking bonds endothermic or exothermic?

endothermic

sp

linear hybridization

Calculating delta S and delta G

same as enthalpy

AX4

tetrahedral

sp3

tetrahedral

sp2

trigonal planar

AX3E

trigonal pyramidal