Chem 100 Week 6

Which of the following values for the principal quantum number corresponds to elements that can accomodate more than four pairs of electrons with other atoms?

Which of the following values for the principal quantum number corresponds to elements that can accomodate more than four pairs of electrons with other atoms?

Which grouping of elements will have similar Lewis symbols?

elements in the same group

Lewis structures can be used for which of the following?

to describe valence electron configurations to indicate the formation of covalent bonds to indicate lone pairs of electrons all of the above Answer Explanation Correct answer: all of the above

Which molecule contains only single bonds?

CO2 NH3 HCN C2H4 Answer Explanation Correct answer: NH3 CO2 and C2H4 contain double bonds, while HCN contains a triple bond, but ammonia has only single bonds.

According to VSEPR theory, electrons in the valence shell of a central atom form __________.

.Correct answer: both lone pairs and bonding pairs of electrons According to VSEPR theory, electrons around a central atom are "electron dense regions." These regions can either be in the form of lone pairs (nonbonding) or in the form of bonding pairs (bonded atoms).

Which molecule will have a net dipole?

Answer Explanation Correct answer: SO2 SO2 has polar bonds and a bent structure, so it will have a net dipole. CO2 and BF3 have polar bonds but molecular structures in which the polarity cancels, producing no net dipole. CH4 has non-polar bonds, so regardless of the molecule structure, it has no net dipole. Your answer:

When the absolute value of the difference in electronegativity of two adjacent atoms in a compound is 1, they are most likely bonded by ________.

Answer Explanation Correct answer: a polar covalent bond. When the absolute value of the difference in electronegativity of two bonded atoms is between 0.4 and 1.8, they tend to form polar covalent bonds.

Which molecule has the most lone pairs?

CH4 NH3 H2O HF Answer Explanation Correct answer: HF The hydrogen fluoride atom will have three lone pairs, whereas water has two, ammonia has one, and methane has none.

Which plot will give a straight line?

Correct answer: V vs. 1/P Boyle's law states P1V1=P2V2. Thus, volume and pressure are inversely related, so only the reciprocal of the pressure against volume results in a linear plot.

The number of bonds an atom can form can be determined by identifying:

Correct answer: the number of electrons needed to form an octet in the valence shell. The octet rule refers to an atom's tendency to gain or lose electrons in order to have a full valence shell of eight electrons. Having this outer shell filled allows the atom to become more stable.

How many electrons does hydrogen need to gain to fill its outermost shell?

Correct answer: 1 The outermost shell (and, in fact, the only valence shell) of hydrogen is n=1, which can only hold two electrons. So hydrogen needs to gain 1 electron to fill its outermost shell.

How many shared electrons and lone pairs does the following molecule have? H-C---C-H

Correct answer: 10 electrons, 0 lone pairs Each line in the Lewis structure is a bond representing a shared pair of electrons. There are 2 single bonds and 1 triple bond which contain 10 shared electrons. There are no lone pairs in this Lewis structure because all of the valence electrons are being shared in bonds.

A molecule with two electron domains will display bond angles of __________ degrees.

Correct answer: 180 A molecule with two electron domains will have 180∘ bond angles in order to make the domains as far from one another as possible. It will be linear.

The octet rule predicts that oxygen will tend to make ____ bond(s).

Correct answer: 2 With two lone pairs and two unpaired electrons, oxygen will gain an octet by making two covalent bonds.

Identify the compound with ionic bonds.

Correct answer: AlBr3 AlBr3 is an ionic compound (metal + nonmetal). Therefore, it has ionic bonds. Cl2 is a diatomic molecule; therefore, it will form a non-polar covalent bond. H2O and NO2 are molecules that consist of nonmetals with different electronegativities; therefore, they will form polar covalent bonds.

Which choice correctly assigns δ+ and δ− to the atoms in the bonds?

Correct answer: C-N, where C is δ+ and N is δ− The correct δ+ and δ− assignment is given for the C-N bond, C is the element with the δ+ and N is the element with the δ−. This is because N is the more electronegative element of the two. Review the following bond polarities and electronegativity differences.

Which of the following is an odd-electron molecule?

Correct answer: ClO2 ClO2 is an odd-electron molecule (7+12=19).

After determining the total number of valence electrons, what is the next step that should be taken when drawing a Lewis structure?

Correct answer: Draw a skeletal structure of the molecule or ion, arranging outer atoms symmetrically around a central atom.

Identify the molecules(s) containing non-polar covalent bonds.

Correct answer: O2 H2 The difference in electronegativity in the S−F bonds in SF6 is 4.0−2.5=1.5. Therefore, the S−F bonds are considered to be polar covalent bonds. The difference in electronegativity in the N−O bonds in NO2 is 3.5−3.0=0.5. Therefore, the N−O bonds are considered to be polar covalent bonds. Thus, only the diatomic molecules O2 and H2 feature non-polar covalent bonds because both atoms have the same electronegativity

When drawing the Lewis structure for a molecule, after drawing the skeletal structure and distributing all of the electrons around the terminal atoms, what actions should be taken if the central atom does not have a complete octet?

Correct answer: Rearrange lone pairs of electrons from the outer atom(s) to form double or triple bonds to the central atom. When drawing the Lewis structure of a molecule, if the central atom lacks an octet, we can move lone pairs of electrons on an outer atom to form a higher order bond (double or triple bond) with the central atom. This preserves the number of electrons for the outer atom so that the octet rule is still satisfied, and increases the number of electrons for the central atom, because shared electron pairs in a bond count as two electrons for both atoms when counting towards the octet rule.

Which of the following is an exception to the octet rule?

Correct answer: Sulfur in SO2−4 Sulfur in SO2−4 is an exception to the octet rule. In this case, sulfur is said to have an expanded octet because it has more than 8 electrons in its valence shell. The Lewis structure for SO2−4 contains two S=O double bonds and two S−O single bonds. These bonds are all covalent bonds, and so the central sulfur atom shares these electron pairs with the oxygen atoms to fill its valence shell. There are 8 electrons in the two S=O double bonds and 4 electrons in the two S−O single bonds. Therefore, the central sulfur atom has 12 electrons in its valence shell.

Select all of the conditions indicated by STP.

Correct answer: T=0∘C P=1atm STP stands for standard temperature and pressure, and it means a temperature of 0∘C, or 273.15K, and a pressure of 1atm, or 760torr. Standard temperature for gas calculations is 0∘C, or 273.15K, and standard pressure is 1atm, or 760torr. Extensive quantities like volume or number of moles (as opposed to molar volume, which is intensive) are not used to define standard conditions.

When drawing the Lewis structure for molecule, if there are any electrons remaining after distributing electrons as lone pairs around the terminal atoms, where are the remaining electrons placed?

Correct answer: The central atom. When drawing the Lewis structure for molecule, if there are any electrons remaining after distributing electrons as lone pairs around the terminal atoms, the remaining electrons are placed on the central atom.

What is pressure?

Correct answer: a measure of force exerted over a given area Pressure is the amount of force exerted over an area perpendicular to it. Thus, the equation for P is, P=F/A The SI unit for pressure is the pascal. One pascal is equal to one newton per square meter. This reinforces the definition of pressure since the Newton is a measure of force, and a square meter is a measure of area. 1 Pa=N/m^2

On the Kelvin scale, 0 is known as __________.

Correct answer: absolute zero On the Kelvin scale, 0 is known as absolute zero. All gas law calculations require that temperatures be on the Kelvin scale. Absolute zero implies that the kinetic energy of all molecules is zero as well.

For which gas will one mole occupy 22.4 liters at standard temperature and pressure?

Correct answer: all of the above Any ideal gas will have the same molar volume, 22.4 liters at STP.

A molecule contains a central atom from Group 13 in the second row of the periodic table. The molecule shows none of the characteristics of a free radical, but will often form bonds with other molecules by accepting a pair of electrons. This molecule is most likely:

Correct answer: an electron-deficient molecule As the central atom of this molecule is in the second row of the periodic table, we know that it cannot be hypervalent. We also know that it cannot have an odd number of electrons, as experimental evidence suggests that it is not a free radical (as all odd-electron molecules are). It is most likely electron-deficient due to the location of its central atom (Group 13) and its tendency to form bonds with molecules containing lone pairs of electrons.

What will be the molecular structure of SO2?

Correct answer: bent With three electron domains, it will have trigonal planar electron-pair geometry. However, with one of them being a lone pair, the structure will be bent. FEEDBACK

A Lewis symbol that has a non-noble gas element and no electrons represents a:

Correct answer: cation Lewis symbols show the valence electrons. If a Lewis symbol has no dots, the atom must have lost its valence electrons, and will therefore be a positively charged cation.

Which of the following is a step in predicting electron pair geometry and molecular structure using VSPER theory? Select all that apply.

Correct answer: count the number of regions of electron density around the central atom write the Lewis structure of the molecule use the number of lone pairs to determine the molecular structure identify the electron-pair geometry based on the number of regions of electron density VSEPR theory can be used to determine both the electron pair geometry and the molecular structure. First, we write the Lewis structure of the molecule, and then count the number of electron dense regions around the central atom. Single bonds, double bonds, triple bonds, and lone pairs each count as one electron dense region. After determining the electron dense regions, the electron pair geometry can be determined based on the number of regions. Finally, we can use the number of lone pairs to determine the molecular structure by focusing on minimizing repulsions.

The number of electron domains surrounding an atom will determine the:

Correct answer: electron-pair geometry Each number of electron domains will correspond with a specific electron-pair geometry.

The element with the highest electronegativity is:

Correct answer: fluorine In general, electronegativity increases from left to right across a period in the periodic table and decreases down a group. Thus, the nonmetals, which lie in the upper right, tend to have the highest electronegativities, with fluorine being the most electronegative element (EN=4.0).

Pressure and volume of an ideal gas are __________.

Correct answer: inversely proportional As volume decreases, the pressure will increase if temperature is kept constant, according to Boyle's law.

If boron only has three valence electrons, it is an exception to the octet rule because

Correct answer: it is an electron-deficient molecule Boron only has three valence electrons, so it can only form three covalent bonds.

Which pair of electron domains generates the most repulsion?

Correct answer: lone pair - lone pair Lone pairs generate the most repulsion as they take up a larger region of space than a bonding pair.

Electron-deficient molecules will react with:

Correct answer: molecules with lone pairs An electron-deficient molecule will react with electron excess, namely a lone pair from some other molecule, like ammonia.

The ________________ an atom attracts the electrons in its bonds, the _______________ its electronegativity.

Correct answer: more strongly, larger Electronegativity is a measure of the tendency of an atom to attract electrons (or electron density) towards itself, and it determines how the shared electrons are distributed between the two atoms in a bond.

which of the following describes Cl2

Correct answer: nonpolar covalent Using the figure, we can determine that Cl2 is nonpolar and covalent (0 electronegativity difference).

In a polar covalent bond, the more electronegative atom will bear a:

Correct answer: partial negative charge Electronegativity is a measure of how strongly an atom attracts electrons to itself. Therefore, the more electronegative atom will have a higher electronegativity value, and it will have a partial negative charge δ−.

Why does water have a net dipole while carbon dioxide does not?

Correct answer: the bond dipoles in carbon dioxide cancel each other out Carbon dioxide is linear, so its bond dipoles are directly opposed and cancel out. Water is bent, so its bond dipoles both point slightly in one direction, giving it a net dipole.

The ideal gas law makes which of the following assumptions? (Select all that apply)

Correct answer: the gas particles are constantly in random motion and have no volume particles do not interact The ideal gas law assumes that particles are infinitely small points in constant, random motion. It does not consider the identity of the gas (whether a noble gas, a diatomic gaseous element like nitrogen, or a gaseous molecule like carbon monoxide) to affect its behavior at all. It also ignores any interactions of these particles, and assumes that they engage in perfectly elastic collisions.

We can predict the number of bonds an atom can form from:

Correct answer: the number of electrons needed to form an octet

Gay-Lussac's law assumes that __________.

Correct answer: the volume is held constant the number of moles is held constant According to Gay-Lussac's law, the pressure and temperature of a gas (in degrees Kelvin) are directly proportional. If one increases, the other one will increase as well (and the same for decrease). This relationship is valid as long as the volume and number of moles of gas are held constant.

What can be used to represent bond dipole moments?

Correct answer: vector Vectors point from the less electronegative atom to the more electronegative atom to indicate the direction of the bond dipole moment. The vector shows that the electrons are pulled from the less electronegative atom toward the more electronegative atom. This separation of charges between the atoms produces a bond dipole moment.

The magnitude of a bond dipole moment is represented by the Greek letter mu (μ) and is a function of the magnitude of the partial charges (Q), and the distance between the charge (r). Which of the following equations accurately represents bond dipole moment?

Correct answer: μ=Qr The magnitude of a bond dipole moment (μ) is given by the formula shown below, where Q is the magnitude of the partial charges (determined by the electronegativity difference) and r is the distance between the charges. μ=Qr This bond dipole moment can be represented as a vector, a quantity having both direction and magnitude.

The Lewis symbol for the chloride ion will have how many dots?

Correct answers:8 If a chlorine atom gains an electron to become the chloride ion, it will have 8 valence electrons and a full valence shell. This means its Lewis symbol will have 8 dots.

Which molecule is electron-deficient?

H2O CH4 BeH2 PCl5 Answer Explanation Correct answer: BeH2 Beryllium has only two valence electrons and thus can only make two bonds. That makes BeH2 electron-deficient as beryllium can't gain an octet.

Which element can form hypervalent molecules?

He Ne Ar Xe Answer Explanation Correct answer: Xe Xenon is large enough that even though it is a noble gas, it can make covalent bonds, many of which result in hypervalent molecules.

Which of the following elements can NOT form hypervalent molecules? (select all that apply)

N S Br B Answer Explanation Correct answer: N B Elements in the second period of the periodic table (n=2) can accommodate only eight electrons in their valence shell orbitals because they have only four valence orbitals (one 2s and three 2p orbitals). Elements in the third and higher periods (n≥3) have more than four valence orbitals and can share more than four pairs of electrons with other atoms because they have empty d orbitals in the same shell. Therefore, of the elements listed above boron and nitrogen can not form hypervalent molecules.

Which is a correct way of stating Gay-Lussac's law?

P=kT P/T=k P1/T1=P2/T2 all of the above Answer Explanation Correct answer: all of the above Gay-Lussac's law, P1/T1=P2/T2, can be mathematically manipulated to yield all of the equations shown. Therefore, these are all valid ways of expressing Gay-Lussac's law.

Which is a correct way of stating Boyle's law?

P=k×1/V, where k is a constant. PV=k, where k is a constant. P1V1=P2V2, where the indices 1 and 2 corresponds to different states of the same gas sample. all of the above Answer Explanation Correct answer: all of the above Boyle's law states that the volume and pressure of a gas vary inversely if the gas is held at a constant temperature. In other words, if the volume is increased by a certain factor, the pressure will decrease by same factor. All three of these equations are ways of expressing this concept mathematically.

Under conditions of constant temperature and amount of substance, a plot of pressure vs. volume for an ideal gas will result in __________.

This plot will give a hyperbolic relationship because there is an inverse relationship between the pressure and the volume of an ideal gas under conditions of constant temperature and constant amount of substance (constant number of moles, n).

Which is a correct way of stating Charles's law?

V=kT V/T=k V1/T1=V2/T2 all of the above Answer Explanation Correct answer: all of the above Charles' law, V1/T1=V2/T2, can be mathematically manipulated to yield any of the equations shown. Therefore, these are all valid ways of expressing Charles's law.

What counts as an electron domain?

a single bond a double bond a lone pair all of the above Answer Explanation Correct answer: all of the above Any kind of bond, as well as a lone pair, will count as one electron domain.

Covalent bonds are formed most frequently between __________.

answer: nonmetals Noble gases rarely form bonds since they already have 8 valence electrons. Metals commonly form either ionic or metallic bonds, depending on the type of element(s) with which they are bonding. Metalloids form covalent, ionic, and metallic bonds. However, it is not as common for this group to form covalent bonds.

What is the relationship between dipole moments and the magnitude of the partial charges?

directly proportional The bond dipole moment is given by the formula: μ=Qr where Q is the magnitude of the partial charges (which is determined by the difference in electronegativity), and r is the distance between the charges. Therefore, the greater the magnitude of the partial charges on the atoms generating the polar bond, the greater the dipole moment.

PV=nRT is the equation for:

ideal gas law

Metals and nonmetals are joined by __________.

ionic bonds

When placing the first electron in a Lewis symbol, it must go:

it does not matter

There can be molecules with polar bonds that are nonpolar overall in which category of electron-pair geometry?

linear trigonal planar tetrahedral all of the above Answer Explanation Correct answer: all of the above Any of these geometries can have nonpolar molecules with polar bonds, because any can consist of bond dipoles that cancel out one another.

Which sample of gas would exert the greatest pressure, assuming that the volume of each sample is the same?

one mole of N2 at 100 K one mole of H2 at 250 K one mole of O2 at 175 K one mole of CO2 at 330 K Answer Explanation Correct answer: one mole of CO2 at 330 K The identity of the gas is irrelevant. If they all are present in the same molar quantity ( 1mole) and at the same volume, the gas at the greatest temperature will exert the greatest pressure.

Which of the following states that the pressure of a given amount of gas is directly proportional to its temperature on the Kelvin scale when the volume is held constant?

orrect answer: Amontons's or Gay-Lussac's law Amontons's or Gay-Lussac's law states that the pressure of a given amount of gas is directly proportional to its temperature on the Kelvin scale when the volume is held constant. This can be seen in P1/T1=P2/T2. As the temperature of a gas increases by a certain factor, the gas pressure will also increase by the same factor. And if the temperature of a gas decreases by a certain factor, the gas pressure will also decrease by the same factor.