homeworks

Calculate the formal charge on N in the molecule NH3.

0 Remember, to calculate formal charge, you take the number of valence electrons an atom has and subtract the number of marks around the atom (count each unshared electron and each bond as a single mark). Formal Charge = ValenceElectrons − number of marks around atom Formal charge for N = 5 - (2 unshared electrons + 3 bonds) = 0

How many double bonds are present in the 'best' resonance structure of the phosphate ion?

1

How many lone pairs of electrons are on nitrogen in NF3?

1

What hybridization would you expect for Se when it is found in SeO42-? A. sp3d B. sp3d2 C. sp2 D. sp3

D. sp3 There are four areas of electron density around Se, giving it a tetrahedral electronic geometry. This corresponds to sp3 hybridization.

Which of the following combinations of hybridization and molecular geometry is possible? A. sp3d, octahedral B. sp2, linear C. sp2, tetrahedral D. sp3, trigonal pyramidal

D. sp3, trigonal pyramidal The hybridization of an atom denotes its electronic geometry. In this case, sp3 denotes a tetrahdral geometry. One of the possible molecular geometries from a tetrahedral electronic geometry is trigonal pyramidal

What is the shape (molecular geometry) of COCl2? A. T-shaped B. tetrahedral C. trigonal pyramidal D. trigonal planar

D. trigonal planar There are three regions of electron density (with no lone pairs) around the central atom. Therefore, the geometry around the central atom is trigonal planar.

Which of the following contains only covalent bonding and no ionic bonding? A. Ca(NO3)2 B. CCl4 C. Na2SO4 D. NaOH

B. CCl4 In Na2SO4, Ca(NO3)2, and NaOH a polyatomic ion is coupled with a metal cation. While covalent bonds attach atoms within the polyatomic ion, ionic bonds connect these polyatomic ions to the metal cations. Only CCl4, which contains 4 C-Cl bonds (which involve bonding between two nonmetallic elements), contains covalent bonds and no ionic bonds.

Which of the following would be expected to have the highest first ionization energy? A. Na B. Xe C. Si D. Cl E. Ar

Ar Ionization energies are highest in the top-right corner of the periodic table.

The sp3 hybridization has what percent s character and what percent p character respectively? A. 75%, 25% B. 25%, 75% C. 50%, 50% D. 33%, 67%

B. 25%, 75% There are 4 orbitals being hybridized, 1 s orbital and 3 p orbitals. What percentage of the orbitals being hybridized are 's' and what percentage are 'p?' s = 1/4 = 25% p = 3/4 = 75%

Which of the following must be observed when filling a molecular orbital energy diagram? A. Aufbau Principle, Conservation of Matter and Energy, and Planck's Law B. Hund's Rule, Pauli Exclusion Principle, and Dalton's Law C. Aufbau Principle, Hund's Rule, and Pauli Exclusion Principle

C. Aufbau Principle, Hund's Rule, and Pauli Exclusion Principle The Aufbau Principle predicts the order of filling electrons in atomic orbitals according to their energies. According to Hund's rule, all orbitals of the same energy level must each receive an electron before pairing of electrons begins. The Pauli Exclusion Principle states that no two electrons in an atom may have all four identical quantum numbers, and therefore only two electrons can fit in any given orbital. All of these rules must be observed when filling a molecular orbital energy diagram.

If the following crystallize in the same type of structure, which has the lowest lattice energy? A. CaO B. SrO C. BaS D. SrS E. BaO

C. BaS Formula units with lower charge densities have lower lattice energies. Since all of the formula units provided have the same charges (+2, -2), their charge density is based on size of the atoms rather than charge. Thus, BaS would have the lowest charge density due to having the largest atoms and, therefore, have the lowest lattice energy.

The electrons in the H 1s orbital and the electrons in the C sp2 hybrid orbital participate in forming the bond. A. 2. 1 B. 2, 3 C. 1, 3 D. 2, 2 E. 3, 1 F. 1, 2 G. 1, 1

D. 2, 2 There is a sigma bond between hydrogen and carbon. There is another sigma bond between carbon and nitrogen. There are two pi bonds between carbon and nitrogen.

What is the expected bond order for the diatomic species B2? A. 4 B. 2 C. 0 D. 1 E. 3

D. 1

A liquid with a high vapor pressure is called... viscous. volatile. cold. hot.

volatile Easily vaporized liquids are called volatile liquids, and they have relatively high vapor pressures.

Which of the following statements regarding intermolecular forces (IMF) is/are true? 1. IMF result from attractive forces between regions of positive and negative charge density in neighboring molecules. 2. The stronger the bonds within a molecule are, the stronger the intermolecular forces will be. 3. Only non-polar molecules have instantaneous dipoles. 1, 2, and 3 2 only 3 only 2 and 3 1 and 3 1 only

1 only Statement 1 is true - all IMF result from Coulombic attraction. Statements 2 and 3 are both false; the strength of the bonds within a molecule have no bearing on the strength of the bonds between molecules; all molecules have London forces.

What is the difference in electronegativity between H and F? Use the below Pauling values and report your answer to one decimal place

1.9 4.0-2.1 = 1.9

Consider a 3-atom molecule A-B-A for which B has a total of only four valence electrons. If you assume that B is a Group II metal, what is the bond angle for A-B-A?

180

How many resonance structures can be drawn for N2O? The atoms are arranged in the following order: N-N-O. Disregard any structure with formal charges other than 0, +1, and -1.

2

What is the bond order of the O‒O bond in O2?

2 Needed electrons: 2x8 = 16 Available electrons: 2x6 = 12 electrons Shared electrons: Needed - Available = 16 - 12 = 4 There are 4 electrons shared in bonds. As all of these electrons must be shared in the O-O bond and 2 electrons form a single bond, there must be a double bond between the oxygens. Thus, the bond order of the O-O bond must be 2.

Based on the general concepts that govern intermolecular attractions, which of the following orderings of fluorocarbons is correct when going from highest to lowest boiling point? 1. CF4 2. F3C-(CF2)4-CF3 3. F3C-(CF2)2-CF3 1, 3, 2 3, 2, 1 1, 2, 3 3, 1, 2 2, 1, 3 2, 3, 1

2, 3, 1 All 3 molecules are non-polar, so their relative boiling points will be governed by their relative weights. Small molecules tend to have low boiling points and large molecules high boiling points.

The carbonate ion (CO32-) has how many resonance configurations?

3

What is the bond order of the C‒C bond in acetylene (ethyne, C2H2)?

3

The diameter of the electron density of an atom is roughly... A. 0.1 - 0.5 nm B. 1 - 5 nm C. None of these. D. 10 - 50 nm

A. 0.1 - 0.5 nm The diameter of the electron density of an atom is roughly 0.1- 0.5 nm.

Consider the elements lithium, oxygen, fluorine, and neon. Based on their position in the periodic table, which element would you expect to have the GREATEST tendency to attract a shared pair of electrons? A. F B. Ne C. Li D. O

A. F Electronegativity (the ability to attract a shared pair of electrons) increases going to the right and upward in the periodic table. However, remember the noble gases do not follow this trend as, even though they are on the right side of the periodic table, they have very little attraction for a shared pair of electrons as their duet and octet rules are already satisfied.

Which of the following elements would be expected to have the highest electronegativity? A. N B. P C. Al D. He E. Na F. C

A. N Electronegativity generally increases from left to right and from bottom to top of the periodic table. The noble gases are excluded in that they are rather inert.

Which substance has polar covalent bonds? A. NH3 B. Ca2C C. Cl2 D. O2

A. NH3 Looking for a covalent substance with the greatest difference in electronegativities between the atoms involved, we find NH3 is the best choice as Cl2 and O2 have differences in electronegativity of 0 and Ca2C is an ionic compound, not a covalent compound

Which of the following has bond angles slightly LESS than 120°? A. O3 B. I3- C. SO3 D. SF2 E. NO3-

A. O3 While SO3 and O3 have three regions of electron density around the central atom, only O3 has a lone pair in one of these regions. The lone pair repels the bonds, forcing them closer together, which makes the angle between the bonds slightly less than 120°.

A chemist has synthesized two new dyes based on the molecular structure of plant-based dyes. The lowest energy absorption line for the first dye is light in the visible region at 530 nm. The lowest energy absorption line for the second dye is light in the visible region at 645 nm. Based on this evidence, which molecule has the larger HOMO-LUMO gap? A. The dye that absorbs at 530 nm. B. The gap is the same as both dyes absorb light in the visible region. C. There is not enough information given to answer the question. D. The dye that absorbs at 645 nm.

A. The dye that absorbs at 530 nm.

Let X be a hypothetical element. Which of the following would be the largest? A. X2‒ B. X‒ C. X D. X2+ E. X+

A. X2‒ X2- would be the largest as it has 2 more electrons than protons, and the protons would be at the greatest disadvantage in this ion when trying to draw the electrons towards the nucleus. In other words, since all of these atoms are the same type of atom, they will have the same number of protons (same atomic number). Therefore, the atom with the greatest number of electrons will be largest as the same number of protons will be less effective at drawing in a larger number of electrons towards the nucleus.

Which of the following statements is NOT correct? Dispersion forces... A. decrease in strength with increasing molecular size. B. are temporary rather than permanent dipole-dipole interactions. C. are also called London forces. D. are the only forces between nonpolar molecules.

A. decrease in strength with increasing molecular size. Polarizability increases with increasing numbers of electrons and, therefore, with increasing sizes of molecules. So, London forces are generally stronger for molecules that are larger or have more electrons.

Forces between particles (atoms, molecules, or ions) of a substance are called... A. intermolecular forces. B. intramolecular forces. C. armed forces.

A. intermolecular forces.

As an atom's radius decreases... A. its ionization energy increases. B. its ionization energy will either increase or decrease depending on whether you are going up a column or across a row. C. its ionization energy does not change. D. its ionization energy decreases.

A. its ionization energy increases. The ionization energy is the amount of energy required to remove the most loosely bound electron. Atoms with smaller radii have higher effective nuclear charge. This means that the electrons will be held more tightly and more energy is required to remove an electron. Thus, the ionization energy increases with decreasing atomic radius.

Consider the molecule B2. What is the magnetism and number of unpaired electrons in B2? A. paramagnetic, 2 B. paramagnetic, 1 C. diamagnetic, 2 D. diamagnetic, 0

A. paramagnetic, 2

Which of the following statements is true about a molecule with a bond order of one? A. The molecule has no electrons in antibonding orbitals. B. The molecule has a single bond. C. Two side-by-side p orbitals combine to form pi bond and pi antibond orbitals; therefore, the bond order is 1. D. The molecule is as stable as molecules with bond orders of two and three

B. The molecule has a single bond.

Which pair of elements is most likely to form an ionic compound? A. nitrogen and sulfur B. magnesium and fluorine C. sodium and aluminum D. oxygen and chlorine

B. magnesium and fluorine Metals and nonmetals tend to form ionic bonds. Nonmetals and nonmetals tend to form covalent bonds. Mg is a metal and F is a nonmetal. N and S are both nonmetals.O and Cl are both nonmetals. Na and Al are both metals.

N2 has a bond order of 3 and O2 has a bond order of 2. Based on this information, choose the response that best completes the following sentence: N2 is (less, more) stable than O2, and has a (larger, shorter) bond length and a (higher, lower) bond energy A. more, shorter, lower B. more, shorter, higher C. less, shorter, lower D. less, longer, lower

B. more, shorter, higher The higher the bond order, the more stable the molecule. Stable bonds have a high bond energy since they are hard to break apart. As bond order increases, the bond length gets shorter. Triple bonds have shorter bond lengths than double or single bonds, and therefore are higher energy and more stable.

Metallic solids are solids composed of metal atoms that are held together by metallic bonds. They also tend to be good conductors because... A. the electrons in metallic solids are tightly bound allowing other electrons to flow freely. B. the electrons in metallic solids are delocalized. C. metals are ductile and can be pulled into wires. D. metals are malleable and can be pounded into sheets.

B. the electrons in metallic solids are delocalized. While metals are ductile and malleable (able to be formed into wires or pounded into sheets), they are also good conductors because their electrons are delocalized to form a "sea of electrons" that allow electrecity (the movement of electrons) to flow freely.

Which of the following atoms has the largest radius? A. Cl B. N C. Br D. F

Br The n quantum number values for the valence electrons of these atoms are F=2, N=2, Cl=3, and Br=4. The larger the principal quantum number of an atom's valence electrons, the larger the radius of that atom.

Write an equation that represents the second ionization energy of nickel. A. Ni(g) ⟶⟶ Ni2+(g) + e- B. Ni(g) ⟶⟶ Ni2+(g) + 2e- C. Ni+(g) ⟶⟶ Ni2+(g) + e- D. Ni(g) ⟶⟶ Ni+(g) + e-

C. Ni+(g) ⟶⟶ Ni2+(g) + e- The first ionization energy of nickel would be represented by ripping an electron off of neutral nickel. Ni(g) ⟶⟶ Ni+(g) + e- The SECOND ionization energy of nickel would be represented by ripping an electron off of nickel that has ALREADY had one electron removed. That is, taking an electron from Ni+. Ni+(g) ⟶⟶ Ni2+(g) + e-

Which of the following compounds contains exactly one unshared pair of valence electrons? A. SiH4 B. C2H4 C. PH3 D. H2S

C. PH3 You can check this structure for correctness by verifying that each atom has the correct number of electrons around it (8 for most elements, 2 for hydrogen) and that the structure shows the correct total number of valence electrons (calculated by adding up the available valence electrons from each atom). The C2H4 molecule contains no unshared pairs; SiH4 contains no unshared pairs; H2S contains 2 unshared pairs.

The dominant forces between molecules are... A. electromagnetic. B. gravitational. C. electrostatic. D. electrodynamic. E. magnetic

C. electrostatic.

The electronegativity of nonmetals is relatively __________ as compared to the electronegativity of metals. A. Depends on the elements being compared. B. the same C. high D. low

C. high Both electronegativity and nonmetallic character increase from left to right and from bottom to top of the periodic table. In general, nonmetals prefer to gain electrons to satisfy their duet/octet rules, but metals prefer to lose electrons to satisfy their duet/octet rules.

Surface tension describes... A. adhesive forces between molecules. B. the forces of attraction between the surface of a liquid and the air above it. C. the inward forces that must be overcome in order to expand the surface area of a liquid. D. the forces of attraction between surface molecules of a solvent and the solute molecules. E. the resistance to flow of a liquid. F. capillary action.

C. the inward forces that must be overcome in order to expand the surface area of a liquid. Molecules in the interior of a liquid interact with molecules all around them, whereas molecules at the surface of a liquid can only be affected by those beneath the surface layer. This phenomenon leads to a net inward force of attraction on the surface molecules, contracting the surface and making the liquid behave as though it had a skin. Surface tension is a measure of the inward forces that must be overcome to expand the surface area of a liquid.

An antibonding orbital is formed when... A. a px-orbital overlaps a pz-orbital. B. a free electron is present in the molecule. C. the overlap of the corresponding atomic orbitals leads to destructive interference. D. an s-orbital overlaps a p-orbital.

C. the overlap of the corresponding atomic orbitals leads to destructive interference.

What is the geometry around the left-most carbon in the molecule CH2CHCH3? A. tetrahedral B. linear C. trigonal planar D. trigonal pyramidal

C. trigonal planar There are three areas of electron density around the left-most carbon in this formula (2 single bonds to hydrogen and 1 double bond to the middle carbon). All areas of electron density are bonds, so this gives the carbon a molecular geometry of trigonal planar.

sp2 hybrid orbitals have... A. tetrahedral symmetry. B. trigonal pyramidal symmetry. C. trigonal planar symmetry. D. linear symmetry

C. trigonal planar symmetry.

Covalent compounds are generally made up of elements found in which part of the periodic table? A. left and right B. lower left C. upper right D. upper left

C. upper right Covalent compounds are formed from elements with small differences in electronegativity, or nonmetal elements. These are found in the upper right corner of the periodic table. Alternatively, very metallic elements are found in the lower left corner of the periodic table.

Resonance is a concept that describes the bonding in molecules... A. by asserting that electrons in a double bond can delocalize (spill over) onto adjacent single bonds to make a bond and a half. B. by asserting that double or triple bonds 'flip' or resonate between two locations in the molecule. C. where there is more than one choice of location for a double or triple bond as deduced from Lewis dot structures. The true bonding is the average over all possible multiple bond locations.

C. where there is more than one choice of location for a double or triple bond as deduced from Lewis dot structures. The true bonding is the average over all possible multiple bond locations. Resonance occurs when there is more than one choice of location for a double or triple bond. The true bonding is the average over all possible multiple bond locations. The arrangement of all possible double bond locations means that a bond may have a bond order of 1.5 or other possibilities such as 1.333 (1 and a third) bonds. Similarly, a 'triple' bond may have a bond order of 2.5 or 2.333.

Which would you expect to have the highest vapor pressure at a given temperature? NaCl C5H12 SBr4 C2H6

C2H6 To evaporate or change phase to a gas, liquids must overcome their IMFs. Therefore, substances with smaller IMFs tend to have higher vapor pressures. C2H6 is the smallest, non-polar molecule of these, so it will have the smallest IMFs and, therefore, have the largest vapor pressure.

Which would you expect to be the most viscous? C4H8 at 30°C C4H8 at 50°C C8H18 at 50°C C8H18 at 30°C

C8H18 at 30°C Viscosity increases as IMFs increase in strength and as the temperature decreases. C8H18 would have higher IMFs than C4H8 since both are nonpolar molecules and larger molecules have greater dispersion forces. In addition, C8H18 at 30°C would be more viscous than at 50°C.

Which of the following molecules are likely to form hydrogen bonds? Select all of the correct answers. CH3COOH CH3CHO CH3CH2OH CH3OCH3

CH3COOH CH3CH2OH Only molecules with H attached to the electronegative atoms N, O, or F can hydrogen bond. Of the molecules given, only CH3COOH and CH3CH2OH have hydrogen attached to oxygen, so these are the only ones that can undergo hydrogen bonding.

Which of the following would you expect to boil at the lowest temperature? C8H18 C3H6 CH4 KF PCl3

CH4 We expect the hydrocarbons CH4, C3H8, and C8H18 to have lower boiling points as they are non-polar and only contain dispersion forces for their IMFs. Of these, CH4 would be the least polarizable as it is the smallest molecule. Thus, CH4 would have the weakest dispersion forces and, therefore, have the smallest boiling point.

In the molecule, C2H4, what are the atomic orbitals that participate in forming the sigma bond between the C and H atoms? A. H: 1s, C: 2p B. H: 1s, C: sp C. H: sp2, C: sp2 D. H: 1s, C: sp2 E. H: 2p, C: sp3

D. H: 1s, C: sp2 The electrons in the H 1s orbital and the electrons in the C sp2 hybrid orbital participate in forming the bond.

Which substance has nonpolar covalent bonds? A. NaCl B. NO2 C. CO D. O2

D. O2 Although oxygen has high electronegativity, the bond between two oxygens will be nonpolar as the difference between the electronegativities of two oxygen atoms is 0.

Which of the following bonds will be the most polar? A. C‒H B. Cl‒O C. C‒N D. S‒F

D. S‒F The most polar bond will occur between the two atoms with the greatest different in their electronegativites. Electronegativites for the atoms involved are: H = 2.20, C = 2.55, S= 2.58, N = 3.04, Cl = 3.16, O = 3.44, F = 3.98 The difference in electronegativites is: Cl-O = 0.28, C-H = 0.35, C-N = 0.49, S-F = 1.40

In a new compound, it is found that the central carbon atom is sp2 hybridized. This implies that... A. carbon has four sigma bonds. B. carbon has four lone pairs of electrons. C. carbon has four regions of high electron density. D. carbon is also involved in a pi bond. E. carbon has a tetrahedral electronic geometry.

D. carbon is also involved in a pi bond.

Very weak and very short range attractive forces between temporary (induced) dipoles are called... A. cohesive forces. B. adhesive forces. C. gravitational forces. D. dispersion forces

D. dispersion forces There are four types of intermolecular forces, listed here in order of decreasing strength: ion-ion interactions (which are so strong they can also be thought of a intramolecular forces), hydrogen bonding, dipole-dipole interactions, and dispersion forces. London forces, dispersion forces, van der Waals, or induced dipoles all describe the same intermolecular force. London forces are induced, short-lived, and very weak. Molecules and atoms can experience London forces because they have electron clouds. London forces result from the distortion of the electron cloud of an atom or molecule by the presence of nearby atoms or molecules.

What hybridization would you expect for C in ethyne (C2H2)? A. sp3 B. sp2 C. sp3d D. sp

D. sp Ethyne is a linear molecule with two central atoms each with 2 areas of electron density. It has sp hybridization.

Which of the following statements concerning molecular orbital theory is true? 1. Bonding orbitals are lower in energy than their corresponding anti-bonding orbitals. 2. If a molecule has an odd number of electrons, then it is paramagnetic. 3. The MO diagrams for O2, F2, Ne2 are NOT filled using the Aufbau principle. A. 1 only B. 2 and 3 C. 2 only D. 1, 2, and 3 E. 1 and 2 F. 1 and 3

E. 1 and 2 Statement 3 is false because molecular orbitals are filled from lowest to highest energy according to the aufbau principle, just like atomic orbitals.

Draw the Lewis structure for NO2-. How many single bonds, double bonds, triple bonds, and unshared pairs of electrons are on the central atom, in that order, when considering a single contributing structure (ignoring the averaging effects of resonance)? A. 0, 0, 1, 1 B. 2, 0, 0, 2 C. 1, 0, 1, 0 D. 4, 0, 0, 0 E. 1, 1, 0, 1

E. 1, 1, 0, 1 Needed electrons: 3 x 8 = 24 Available electrons: 5 + (2 x 6) + 1 = 18 # of bonds: (24-18)/2 = 3 bonds The Lewis structure for NO2- can be found by connecting the oxygen atoms to nitrogen and placing eight electrons around each atom. The central atom has one single bond, one double bond, and one unshared pair of electrons.

Which of the following statements concerning molecular orbital theory is/are true? 1. Bonding orbitals are equal in energy to their corresponding anti-bonding orbitals. 2. Adding electrons to anti-bonding orbitals destabilizes molecules. 3. Unlike when we fill atomic orbitals, we DON'T use Hund's Rule to fill molecular orbitals. A. 3 only B. 1 and 3 C. 1, 2, and 3 D. 1 only E. 2 only F. 2 and 3

E. 2 only Statement 1 is false because bonding orbitals are lower in energy than their corresponding anti-bonding orbitals. Statement 3 is false because degenerate molecular orbitals are half-filled before being completely filled, according to Hund's rule, just like atomic orbitals.

Which of the following species possesses a delocalized bond? A. NCl3 B. No molecule given here possesses a delocalized bond. C. H2S D. H2O E. NO3-

E. NO3-

Which of the following demonstrates the formation of an ionic compound involving the elements Na and S? A. Na+ + Na+ + Na+ + S3- ⟶⟶ Na3S B. Na2+ + S2- ⟶⟶ NaS C. Na+ + S- ⟶⟶ NaS D. Na2+ + Na2+ + Na2+ + S3- + S3- ⟶⟶ Na3S2 E. Na+ + Na+ + S2- ⟶⟶ Na2S

E. Na+ + Na+ + S2- ⟶⟶ Na2S Na gives up an electron to form the Na+ cation and S acquires two electrons to form the S2- anion. Balancing this exchange of electrons, we get: Na+ + Na+ + S2- ⟶⟶ Na2S

Which of the following is a polar molecule? A. SO3 B. CO2 C. CCl4 D. XeF2 E. SF4

E. SF4 Each molecule listed has polar bonds arranged symmetrically around the central atom except for SF4. SF4 has a lone pair and see saw geometry, which gives it an asymmetric distribution of electrons around the central atom S. So, SF4 is a polar molecule.

Determine the molecular geometry of the ion NO2-. A. trigonal planar B. linear C. trigonal pyramidal D. none of these E. bent or angular

E. bent or angular The central atom N has 2 bonding regions and 1 lone pair of electrons. The three areas of high electron density make the electronic geometry trigonal planar and the molecular geometry bent or angular.

A sigma bond... A. is always polar. B. is composed of non-bonding orbitals. C. stems from sp hybridization of orbitals. D. always exists in conjunction with a pi bond. E. may exist alone or in conjunction with a pi bond.

E. may exist alone or in conjunction with a pi bond.

Which of the following structures represents a possible hydrogen bond? F-H ······ F Cl-H ······ Cl C-H ······ O Br-H ······ Br

F-H ······ F H-bonds are a special case of very strong dipole-dipole interactions. They only occur when H is bonded to small, highly electronegative atoms - F, O, or N only.

Put the following compounds in order of increasing melting points. LiF, HF, F2, NF3 LiF, HF, F2, NF3 LiF, HF, NF3, F2 F2, NF3, LiF, HF F2, NF3, HF, LiF

F2, NF3, HF, LiF F2 is nonpolar and will therefore have the weakest IMF. NF3 is polar and will have dipole-dipole interactions, which are stronger IMFs. Stronger still is HF which can perform hydrogen bonding. Finally, LiF is ionic and held together by ionic interactions, the strongest IMFs of all. The stronger the IMFs holding molecules together, the more energy is required to separate the molecules and, thus, the higher the boiling point for the substance. So, the molecules listed in increasing order of IMF strength and, therefore, increasing order of boiling points are: F2, NF3, HF, LiF.

Which of the following is not correctly paired with its dominant type of intermolecular forces? NH3, hydrogen bonding HBr, hydrogen bonding C6H6 (benzene), instantaneous dipoles SiH4, instantaneous dipoles CaO, ionic forces

HBr, hydrogen bonding HBr is a polar molecule that does not contain H bonds. Therefore, dipole-dipole forces will be the most significant type of intermolecular forces present.

Which of KBr or CH3Br is likely to have the higher normal boiling point? It is impossible to tell. CH3Br KBr

KBr KBr is an ionic compound as opposed to the molecular compound CH3Br. As ionic interactions are stronger than dipole-dipole interactions, we expect KBr to have a higher boiling point. In fact, KBr boils at 1435°C and CH3Br boils at 3.6°C.

What type of intermolecular forces would you expect to find in a pure liquid sample of carbon tetrachloride? hydrogen bonding London dipole-dipole interionic (ionic)

London Carbon tetrachloride is nonpolar. Nonpolar molecules only exhibit London forces (aka dispersion forces) as their IMFs.

Identify the kinds of intermolecular forces that might arise between molecules of N2H4. London forces London forces, dipole-dipole Hydrogen bonding London forces, dipole-dipole, and hydrogen bonding

London forces, dipole-dipole, and hydrogen bonding All molecules participate in London forces. N2H4, however, is also polar and can therefore also perform dipole-dipole interactions. In fact, the polar bonds shown connect hydrogen to a very electronegative atom, N. Thus, this molecule can also perform hydrogen bonding.

Rank the following in order of increasing vapor pressure at a fixed temperature: H2O, CH3Cl, He, NaCl NaCl < H2O < CH3Cl < He He < H2O < CH3Cl < NaCl H2O < CH3Cl < He < NaCl H2O < NaCl < CH3Cl < He He < CH3Cl < H2O < NaCl

NaCl < H2O < CH3Cl < He Ordering these in terms of increasing vapor pressure is the same as ordering them in terms of decreasing IMF. This order is: NaCl < H2O < CH3Cl < He because NaCl is ionic, H2O can perform hydrogen bonding, CH3Cl is polar, and He is nonpolar.

Predict which of butane (C4H10) or propanone (CH3COCH3) has the greater viscosity. Assume that they are both at the same temperature and in their liquid form. They have equal viscosities. It's impossible to know. butane propanone

Propane Propanone (aka acetone) should be more viscous than butane because it is more polar than butane.

For which of the following elements would the size of the neutral atom (atomic radius) be the largest? A. Na B. Rb C. Ca D. Sr

Rb Atomic radii become larger as you move from right to left across a row or as you move down a column. Diagonal relationships can be tricky, especially when you have to decide which of the two relationships will be the most important. Here, luckily, the comparison works well. With each successive member of a column, you are introducing a new energy level, farther and farther from the nucleus. The largest radius here would then belong to the element which sits closest to the bottom left corner of the periodic table, which is Rb.

Which of the following solids is a covalent network? CaCO3(s) SiO2(s) H2O(s) Ni(s)

SiO2(s)

Which of the following, in the solid state, would be an example of a molecular crystal? iron carbon dioxide diamond calcium fluroide

carbon dioxide CO2 is a covalent molecule. Any extended lattice among covalent molecules will be held together by intermolecular forces. In this case, carbon dioxide is held together with dispersion forces and dipole-dipole interactions. Covalent bonds are not found between CO2 molecules, only within the molecule. Therefore, the crystal will be molecular.

Which of the following, in the solid state, would be an example of a covalent crystal? diamond barium fluoride water iron carbon dioxide

diamond Covalent crystals are held together by covalent bonds in an extended, rigid crystalline network. Diamond is a covalent crystal of carbon.

What would be the most significant type of intermolecular forces in a liquid sample of fluoroform (CHF3)? ionic dipole-dipole hydrogen bonding dispersion covalent

dipole-dipole London forces, dispersion forces, van der Waals or induced dipoles all describe the same intermolecular force. London forces are induced, short-lived, and very weak. Molecules and atoms can experience London forces because they have electron clouds. London forces result from the distortion of the electron cloud of an atom or molecule by the presence of nearby atoms or molecules. Permanent dipole-dipole interactions are stronger than London forces and occur between polar-covalent molecules such as fluoroform here. H-bonds are a special case of very strong dipole-dipole interactions. They only occur when H is bonded to small, highly electronegative atoms - F, O, or N. Ion-ion interactions are the strongest due to extreme charge separation and occur between ionic molecules. They can be thought of as both inter- and intramolecular bonding. Covalent bonding is stronger than any of these, but they are specifically a type of intramolecular bonding, not intermolecular bonding. CHF3 is a polar molecule that does not contain H bonds. Therefore, dipole-dipole forces will be the most significant type of intermolecular forces present.

What is the predominant intermolecular force between IBr molecules in liquid IBr? hydrogen bonds dispersion forces covalent bonds dipole forces ionic forces

dispersion forces You might have thought that dipole forces was right. The fact is that the dipole between iodine and bromine is incredibly weak- too weak to account for the fact that this compound is a liquid. Dispersion forces are actually the dominant forces here due to the SIZE of these atoms and, hence, the size of the molecule. Just know that not ALL dipole forces are bigger than any set of dispersion forces. Size matters, and dispersion forces win out here.

Diamond and graphite are two crystalline forms of carbon. In which form are the C atoms arranged in flat sheets with one C bonded to three nearby C atoms? diamond neither of these graphite

graphite

The vapor pressure of all liquids... increases with temperature. is the same at 100°C. is the same at their freezing points. decreases if the volume of the container increases.

increases with temperature. As temperature (kinetic energy) increases, rate of evaporation increases and rate of condensation decreases. Therefore, vapor pressure will increase with increasing temperature.

Which of the following interactions is generally the strongest? dipole-dipole interactions hydrogen bonding dispersion forces ionic interactions

ionic interactions All molecules perform dispersion forces, intermolecular forces that appear and disappear due to instantaneous partial charges in molecules. Dipole-dipole interactions occur when a polar molecule contains permanent partial charges. Hydrogen bonding is a special type of dipole-dipole interaction that is stronger than most and occurs when hydrogen is specifically attached to either a N, O, or F atom. Even stronger than hydrogen bonding are ionic interactions that occur between atoms or molecules with full charges. These interactions are so strong, they can even be considered intermolecular forces as well as intramolecular forces. Thus, in order of strength (weakest to strongest), we have dispersion forces (aka London forces or van der Waals forces), dipole-dipole interactions, hydrogen bonding, and ionic interactions.

Which is the correct order of increasing bond strength?

single, double, triple

Which of the following, in the solid state, would be an example of an ionic crystal? carbon dioxide copper sodium nitrate diamond

sodium nitrate

A drop of liquid tends to have a spherical shape due to the property of... capillary action. close packing. vapor pressure. surface tension viscosity

surface tension Molecules on the surface of a liquid are influenced by intermolecular attractions towards the interior; these attractions pull the surface layer towards the center. The most stable situation is one in which the surface area is minimal. For a given volume, a sphere has the least possible surface area. Thus, intermolecular forces cause the liquid to bead up, and we call this property surface tension.

Tetrabromomethane has a higher boiling point than tetrachloromethane. true false

true In general, the stronger the intermolecular forces, the higher the boiling point of the substance. Both molecules are non-polar, so they only exhibit dispersion forces. However, as Br is larger than Cl, tetrabromomethane (CBr4) is larger than tetrachloromethane (CCl4), and therefore CBr4 has stronger dispersion forces.