CH304K Exam 2

Determine the molecular geometry of the molecule NH2Cl.

trigonal-pyramidal

Photosynthesis is the process in which a plant uses energy from the sun to...

... help convert CO2 from the air into plant tissue.

How many lone pairs should appear on the central atom in the dot formula for the chlorate ion ClO3-? 1. 1 2. 8 3. 2 4. 4 5. 3

1 Explanation: See Lewis dot structure.

Why doesn't high intensity microwave radiation cause the same kind of skin cancer caused by ultraviolet radiation?

Microwave photons do not have enough energy to break apart a biological molecule. Explanation: UV radiation is high enough in energy to be able to break bonds in molecules such as DNA. Although microwave photons do possess some energy, in order for enough energy to be put into a molecule to cause a bond to break, many (millions) of microwave photons would need to be absorbed by the same molecule simultaneously, which is unlikely!

What are the similarities between the North Pole and South Pole that indicate the possibility of a northern hemisphere ozone hole formation?

Presence of chlorine-containing species and polar stratospheric clouds.

Which of the species, if any, listed below are radicals? (O2)-, XeO4, CH3O, (HXeO4)-

(O2)- and CH3O Explanation: Radicals are species with an unpaired electron, so only (O2)- and CH3O are radicals.

Which of the following does NOT exhibit resonance while strictly following the octet rule? 1. All other answers have ions or molecules which exhibit resonance. 2. NO3- 3. (CO3)2- 4. O3 5. (SO3)2-

(SO3)2- Only one Lewis structure can be drawn for (SO3)2-, so it does not exhibit resonance. This structure satisfies the octet rule for each atom and has 26e−. All of the other molecules listed can have at least two correct but different Lewis structures drawn for them. Calculate (S/2)/B; if you get a fraction greater than one, that molecule exhibits resonance. The Lewis dot structure for SO3 contains 2S O single-bonds and 1 S---O double bond. You can draw three different structures for SO3. Also, (S/2)/B = (4/2)/3 = 2/3 = 0.66; fractions indicate resonance or delocalization of electrons.

The number of shared electrons that should appear in the dot formula for the chlorate ion (ClO3-) is 1. 6 2. 8 3. 4 4. 10 5. 2

6 Explanation: To draw the dot structure for ClO3- we must first calculate the number of valence electrons available from the atoms: 1×7e− (fromCl)+3×6e− (fromO) +1 e− (from −1 charge) = 26e− We choose the least electronegative element as the central atom (chlorine in this case) and place the other atoms symmetrically around it. The correct dot structure for the molecule should show a complete octet (8 electrons) around each atom and a total of 26 valence electrons for the entire structure. There are 3 bonds in the structure. Each bond consists of two electrons, so there are 6 shared electrons in the structure. (If using the S = N − A rule to determine the dot structure, N = (8×1)+(8×3) = 32 e− and S = 32−26 = 6 e−. This would indicate 3 bonds and correspond to the structure shown above.)

What evidence established the conclusion that global temperatures and atmospheric CO2 concentrations have been correlated for more than 150,000 years?

CO2 concentrations found in bubbles in ice cores correlate with deuterium (2H) to hydrogen (1H) ratios that provide the temperature record.

What chemical species is responsible for much of the destruction of the ozone?

Cl Explanation: Rowland and Melina showed the Cl• radical acts as a catalyst in a series of reactions that convert O3 to O2.

Resonance is a concept that describes the bonding in molecules 1. where there is more than one choice of location for a double bond as deducted from Lewis dot structures. The true bonding is the average overall possible double bond locations. 2. by asserting that double bonds "flip" or resonate between two locations in the molecule. 3. by asserting that electrons in a double bond can delocalize (spill over) onto adjacent single bonds to make a bond and a half.

Where there is more than one choice of location for a double bond as deducted from Lewis dot structures. The true bonding is the average overall possible double bond locations. Explanation: In resonance, although the arrangement of all possible double bond locations may sometimes mean that a double bond has a bond order of 1.5, other possibilities can occur, such as 1.333 (1 and a third bonds).

In fossil fuels you would expect

relatively low 14C concentrations.

The carbon cycle refers to

the movement of carbon through living organisms, the atmosphere, the sea, and the earth.

The Montreal protocol is a...

treaty to reduce the amount of CFCs produced in the world.

DNA, the genetic material of living organisms, is damaged by light in the

ultraviolet (UV) region, especially below a wavelength of 320 nm. Explanation: UV photons have enough energy to break bonds in molecules (such as DNA). UV wavelengths below about 320 nm are increasingly more damaging to biological species.

Infrared radiation causes molecules to

vibrate.

The Lewis dot formula for Br2 shows 1. A total of 8x2=16 electrons 2. A single ionic bond 3. A double covalent bond 4. A single covalent bond 5. A triple covalent bond

A single covalent bond. Explanation: The bromine-bromine bond (between two nonmetal atoms) will be a covalent bond. To draw the dot structure for Br2 we must first calculate the number of valence electrons available from the atomsL A = 7 electrons x 2 Br atoms = 14e- The correct dot structure for the molecule should show a complete octet (8 electrons) around each atom and a total of 14 valence electrons for the entire structure. (If using S=N-A rule to determine the dot structure, N=8x2=16e- and S=16-14=2e-. This would indicate 1 bond)

What is FALSE about UV-A radiation? 1. All UV-A radiation wavelengths are screened by ozone. 2. UV-A radiation can cause skin cancer. 3. UV-A radiation causes wrinkling of the skin. 4. UV-A radiation is the lowest energy among the three types of UV (UV-A, UV- B, and UV-C).

All UV-A radiation wavelengths are screened by ozone.

Decreased stratospheric ozone concentrations: 1. may lead to increased incidences of melanomas. 2. may lead to an increased occurrence of cataracts. 3. All of these 4. may lead to a decreased production of crops such as wheat, sorghum and peas.

All of these Explanation: With less ozone, more UV-B will reach the earth's surface; this radiation can break bonds in molecules such as DNA, leading to cancers. UV-B can also damage crops and create cataracts.

What is the relationship between stratospheric levels of atomic chlorine and ozone?

As chlorine increases, ozone decreases. Explanation: Chlorine atoms are catalysts for ozone- destroying reactions.

HFCs may be used to replace CFCs. Which compound is an HFC? 1. CH2F2 2. CH2ClF 3. CHCl2 − CCl2F 4. CF2HCHClF

CH2F2 Explanation: HFC is a hydrofluorocarbon; it has no chlorine in it.

Which of the following is polar? 1. CH3Cl 2. CCl4 3. CH4 4. (NO3)- 5. CO2

CH3Cl

The electronegativity of an atom generally _____ going down columns and ______ going left to right across rows. An element like fluorine would most likely form a(n) _______ bond with an element like oxygen.

Decreases, Increases, Covalent

The octet rule is applied to bonding in carbon-containing compounds. In accordance with the octet rule, 1. all carbon-containing compounds contain at least eight bonds. 2. each bonded carbon atom forms 8 bonds. 3. the number of atoms in any carbon-containing compound is a multiple of eight. 4. each bonded carbon atom shares electrons so that it has exactly eight outer shell electrons.

Each bonded carbon atom shares electrons so that it has exactly eight outer shell electrons. Explanation: Carbon already has four valence electrons, so it only needs four more to make four bonds.

Which group on the periodic table contains at least one element likely to form stable covalent compounds that have fewer than 8 valence electrons on their central atom? 1. Group 5 2 Group 4 3. Group 3 4. Group 6 5. Group 7

Group 3

Which of the following molecules would have linear molecular geometry? 1. H2O 2. SO2 3. All of the molecules listed 4. None of the molecules listed 5. HCN

HCN

It would NOT be feasible to make ozone and transport it up into the stratosphere to replenish the lost ozone because: I. it would require millions of plane loads II. scientists cannot manufacture ozone III. the catalysts would still be there, so the equilibrium concentration would not change much.

I and III

Which of the occurrences or processes is/are expected to reduce the level of atmospheric carbon? I) formation of carbonate rock in the ocean II) animal respiration III) the growth of trees IV) decaying plant and animal remains

I and III only

Which of statement(s) is a/are part(s) of the Chapman cycle in the stratosphere? I) Ozone is removed by an interaction withUV radiation causing it to dissociate into an oxygen molecule and an oxygen atom II) Ozone is removed by its reaction with water vapor III) Ozone reacts with oxygen atoms to formoxygen molecules.

I and III only. Explanation: The Champman cycle is: 1)O2 +UV→2O 2) O2 + O → O3 3) O3 + UV → O2 + O 4)O3 +O→2O2

Earth's atmosphere is mostly transparent to which forms of light energy? I) infrared II) long wavelength UV (UV-A) III) short wavelength UV (UV-C) IV) visible

II and IV

In order for a molecule to absorb infrared radiation which of the following must be true? 1. It must have polar bonds. 2. It must be a homonuclear diatomic. 3. It must have polar bonds AND at least one of the molecule's vibrations must result in a change in the distribution of electric charge. 4. It must be able to rotate. 5. It must have polar bonds AND be a homo-nuclear diatomic. 6. It must contain more than one isotope of each of its elements.

It must have polar bonds AND at least one of the molecule's vibrations must result in a change in the distribution of electric charge.

An element E has the electron configuration 1s2 2s2 2p4. What is the formula of its compound with lithium? 1. LiE2 2. LiE 3. Li4E 4. Li2E

Li2E Explanation: E is oxygen. Since it has six valance electrons, it forms a 2-ion isoelectronic with Ne.

Which statement is FALSE? 1. Lone pairs of electrons are considered a part of the description of the electronic geometry about a central atom. 2. Lone pairs of electrons repel each other more strongly than bonding pairs repel each other. 3. Lone pairs of electrons on the central atom have no effect on the molecular geometry of a molecule or polyatomic ion. 4. Lone pairs of electrons repel each other more strongly than they repel bonding pairs. 5. Lone pairs of electrons are not considered a part of the description of the molecular geometry about a central atom.

Lone pairs of electrons on the central atom have no effect on the molecular geometry of a molecule or polyatomic ion.

Which pair of elements is most likely to form an ionic compound? 1. Sodium and Aluminum 2. Nitrogen and Sulfur 3. Magnesium and Fluorine 4. Oxygen and Chlorine

Magnesium and Fluorine Explanation: 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.

What is NOT an important factor leading to the ozone hole over Antarctica? 1. the spring sun 2. a climatic vortex (swirling winds) that traps chlorine-containing molecules over Antarctica 3. polar stratospheric clouds 4. a complex mix of chlorine-containing molecules that include, for example, ClO, Cl2O2, etc. 5. nitric oxide radicals

Nitric Oxide Radicals

Which substance has nonpolar covalent bonds? 1. NaCl 2. CO 3. NO2 4. O2

O2

The Lewis dot structure for an isolated silicon atom has: 1. Two pairs of electrons 2. One pair of electrons and two lone electrons 3. Three pairs of electrons 4. Four lone electrons 5. One pair of electrons and three lone electrons

One pair of electrons and two lone electrons Explanation: By Hund's rule, degenerate orbitals are first filled singly before pairing up electrons with opposite spins.

Lewis dot structures provide a simple rationalization for the fact that O3 absorbs light of larger wavelengths than O2 . The rationalization is that: 1. O3 is found higher up in the atmosphere where there is more UV light. 2. O3 is a cyclic molecule. 3. O3 vibrational frequencies are lower, making it easier to dissociate the molecule with light. 4. O3 is a radical. 5. resonance structures show that O3 has one and a half bonds between each pair of atoms whereas O2 is double bonded.

Resonance structures show that O3 has one and a half bonds between each pair of atoms whereas O2 is double bonded.

Of the following five gases, which could be a greenhouse gas? Cl2, SF6, CH4, He, NO2

SF6, CH4, NO2 only.

Which Compound is likely to have a low melting point? 1. Magnesium Oxide 2. None of these Molecules 3. Barium Fluoride 4. Sulfur Trioxide 5. Calcium Chloride

Sulfur Trioxide

Which statement is correct? 1. The desirable properties of CFCs has led to their use in a wide variety of applications. 2. There is no evidence that CFCs are contributing to the destruction of the ozone layer. 3. CFCs are toxic and corrosive. 4. HCFCs have no chlorine in them.

The desirable properties of CFCs has led to their use in a wide variety of applications.

From what column must atom A come in the Lewis dot structure for CH3A? The central atom is carbon. It is bonded to three hydrogen atoms and single-bonded to A. Both carbon and A follow the octet rule. 1. II 2. IV 3. V 4. VII 5. VI 6. VIII 7. III

VII Explanation: Since A follows the octet rule, it must have 3 lone pairs around it. The structure has 14 valence electrons. H 3x1e- =3e- C 1x4e- = 4e- A 1x?e- = xe- 3e- + 4e- + xe- = (7+x)e- 7+x=14 so x=7 and A comes from group VII.

What step does NOT contribute to the greenhouse effect? 1. Visible and ultraviolet light are absorbed by the earth's surface, including the oceans. 2. Vibrating molecules emit infrared radiation. 3. Atmospheric CO2 absorbs infrared radiation. 4. Energy deposited in the Earth's surface is degraded to heat, which causes molecules to vibrate. 5. Visible and ultraviolet light are absorbed by the atmosphere.

Visible and ultraviolet light are absorbed by the atmosphere.

The strongest evidence that CFCs are respon- sible for the depletion of the ozone layer is...

the correlation between stratospheric chlorine and fluorine concentrations and the fact that there are essentially no natural sources of atmospheric fluorine. Explanation: The data gathered by NASA and by international researchers established that high concentrations of HCl and HF always occur together. Although some of the HCl might conceivably arise from a variety of natural sources, the only reasonable origin of significant stratospheric HF is CFCs.

The VSEPR theory is based on

the minimization of repulsion among valence electron pairs.

How many double and triple bonds are in the compound CH2CCHCH2CCH?

2 double, 1 triple.

The ozone layer selectively protects us from damaging ultraviolet radiation over the region:

242 nm < λ < 320 nm

How many fluorine atoms are there in CFC-113?

3

The CENTRAL atom is N. Draw the Lewis structure for NH2Cl. How many single bonds, double bonds, triple bonds, and unshared pairs of electrons are on the central atom, in that order?

3, 0, 0, 1

How many valence electrons must be shown in the dot formula for the C3H8N2O molecule? 1. 64 2. 44 3. 30 4. 36 5. 28

36 Explanation: To find the total number of valence electrons available for the dot formula we sum the number of valence electrons in each atom of the molecule. Carbon has 4 valence electrons and there are 3 C atoms. Hydrogen has 1 valence electron and there are H atoms. Nitrogen has 5 valence electrons and there are 2 N atoms. Oxygen has 6 valence electrons and there is 1 O atom. Total valence e- = (4*3)+(1*8)+(5*2)+(6*1) = 36

If chlorine atoms have a strong tendency to achieve an octet by combining and sharing electrons with another atom, why do chlorine atoms react with O3 and O atoms in the ozone layer rather than with other chlorine atoms? 1. O3 and O do not have any electrons in their outer shells to share. 2. There are so few chlorine atoms in the air that they rarely meet to combine. 3. Other chlorine atoms do not have any electrons in the outer shell to share. 4. Other chlorine atoms do not want to share their electrons.

There are so few chlorine atoms in the air that they rarely meet to combine. Explanation: Oxygen, but not chlorine, is a natural constituent of the atmosphere.

Why do ionic compounds tend to conduct electricity when they melt?

They are no longer held rigidly together.

Why do you wear sunscreen to protect your skin from some of the sun's radiation?

To absorb UV-A and UV-B radiation.

True or False: If HCl is covalently bound as a gaseous molecule but reacts when dissolved in water to form ions, we would conclude that gas phase HCl is an insulator and aqueous HCl is a conductor.

True Explanation: Ions conduct electricity.