Principles of Chemistry

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Chapter 6: Electronic Structure and Periodic Properties of Elements

9.6 Non-Ideal Gas Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506

13.3 Shifting Equilibria: Le Châtelier’s Principle

17.5 Batteries and Fuel Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 960

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Portrait of a Chemist features present a short bio and an introduction to the work of prominent figures from history and present day so that students can see the “face” of contributors in this field as well as science in action.

Please consider, however, that the chapters were not written to be completely independent, and that the proposed alternate sequence should be carefully considered for student preparation and textual consistency.

Chemical substances and processes are essential for our existence, providing sustenance, keeping us clean and healthy, fabricating electronic devices, enabling transportation, and much more.

Humans began to practice chemistry when they learned to control fire and use it to cook, make pottery, and smelt metals.

The practice of chemistry is not limited to chemistry books or laboratories: It happens whenever someone is involved in changes in matter or in conditions that may lead to such changes.

Scientific progress is seldom neat and clean: It requires open inquiry and the reworking of questions and ideas in response to findings.

One of the features that makes chemistry fascinating is the use of a domain that must be imagined to explain behavior in a domain that can be observed.

A plasma is a gaseous state of matter that contains appreciable numbers of electrically charged particles.

She may feel “weightless” during her trip when she experiences negligible external forces (gravitational or any other), although she is, of course, never “massless.”

To put this in perspective, if a carbon atom were the size of a dime, the cross-section of one strand would be larger than a football field.

If an ordinary glass of water were enlarged to the size of the earth, the water molecules inside it would be about the size of golf balls.

Free sodium, an element that is a soft, shiny, metallic solid, and free chlorine, an element that is a yellow-green gas, combine to form sodium chloride (table salt), a compound that is a white, crystalline solid.

Oxygen constitutes nearly one-half and silicon about one-quarter of the total quantity of these elements.

About 30% of the elements that are found in nature are found within a typical smart phone.

Nitroglycerin is very dangerous because it explodes easily; neon poses almost no hazard because it is very unreactive.

A drop of hot cooking oil spattered on your arm causes brief, minor discomfort, whereas a pot of hot oil yields severe burns.

Without units, a number can be meaningless, confusing, or possibly life threatening.

A meter was originally specified as 1/10,000,000 of the distance from the North Pole to the equator.

In order to swindle people into paying for a brick of gold without actually investing in a brick of gold, people have considered filling the centers of hollow gold bricks with lead to fool buyers into thinking that the entire brick is gold.

Counting is the only type of measurement that is free from uncertainty, provided the number of objects being counted does not change while the counting process is underway.

In the number 21.6, then, the digits 2 and 1 are certain, but the 6 is an estimate.

Do you think the US population was correctly determined to the reported nine significant figures, that is, to the exact number of people?

In the midst of all these technicalities, it is important to keep in mind the reason why we use significant figures and rounding rules—to correctly represent the certainty of the values we report.

Precise values agree with each other; accurate values agree with a true value.

Dimensional analysis is based on this premise: the units of quantities must be subjected to the same mathematical operations as their associated numbers.

Regardless of the details, the basic approach is the same—all the factors involved in the calculation must be appropriately oriented to insure that their labels (units) will appropriately cancel.

The Celsius and Fahrenheit temperature scales, however, do not share a common zero point, and so the relationship between these two scales is a linear one rather than a proportional one.

Very few countries (the U.S. and its territories, the Bahamas, Belize, Cayman Islands, and Palau) still use Fahrenheit for weather, medicine, and cooking.

Chemists use the scientific method to perform experiments, pose hypotheses, and formulate laws and develop theories, so that they can better understand the behavior of the natural world.

Heat is an example of an extensive property, and temperature is an example of an intensive property.

Identify each of the underlined items as a part of either the macroscopic domain, the microscopic domain, or the symbolic domain of chemistry.

The dough is cooked in an oven at 350 °F releasing a wonderful aroma of freshly baked bread during the cooking process. Is the mass of the baked loaf less than, greater than, or the same as the one pound of original dough?

Considering that mass and volume are both extensive properties, explain why their ratio, density, is intensive.

Indicate whether each of the following can be determined exactly or must be measured with some degree of uncertainty: (a) the number of eggs in a basket (b) the mass of a dozen eggs

Many chemistry conferences have held a 50-Trillion Angstrom Run (two significant figures). How long is this run in kilometers and in miles?

Osmium is one of the densest elements known. What is its density if 2.72 g has a volume of 0.121 cm3?

Scientists are working to develop biomarker “fingerprints” that could be used to diagnose a specific disease based on the amounts and identities of certain molecules in a patient’s exhaled breath.

Interestingly, these philosophers thought about atoms and “elements” as philosophical concepts, but apparently never considered performing experiments to test their ideas.

These ratios by themselves may not seem particularly interesting or informative; however, if we take a ratio of these ratios, we obtain a useful and possibly surprising result: a small, whole-number ratio.

This 2-to-1 ratio means that the brown compound has twice the amount of chlorine per amount of copper as the green compound.

The particles are attracted by positive (+) charges and repelled by negative (−) charges, so they must be negatively charged.

It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of paper and it came back and hit you.

It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.

If the nucleus were the size of a blueberry, the atom would be about the size of a football stadium.

An observant student might notice that the sum of an atom’s subatomic particles does not equal the atom’s actual mass.

To avoid confusion with other notations, only the first letter of a symbol is capitalized.

Hydrogen-2, symbolized 2H, is also called deuterium and sometimes symbolized D. Hydrogen-3, symbolized 3H, is also called tritium and sometimes symbolized T.

It is important to understand that no single boron atom weighs exactly 10.8 amu; 10.8 amu is the average mass of all boron atoms, and individual boron atoms weigh either approximately 10 amu or 11 amu.

These cations then pass through a (variable) electric or magnetic field that deflects each cation’s path to an extent that depends on both its mass and charge (similar to how the path of a large steel ball bearing rolling past a magnet is deflected to a lesser extent that that of a small steel BB).

The symbols H, 2H, H 2, and 2H 2represent very different entities.

He wonders if we could “make a really cool universal chemistry set” by what he calls “app-ing” chemistry.

What Apple did for music, I’d like to do for the discovery and distribution of prescription drugs.

But Mendeleev went one step further than Meyer: He used his table to predict the existence of elements that would have the properties similar to aluminum and silicon, but were yet unknown.

Hydrogen is a unique, nonmetallic element with properties similar to both group 1A and group 7A elements.

The transfer and sharing of electrons among atoms govern the chemistry of the elements.

In fact, transition metals and some other metals often exhibit variable charges that are not predictable by their location in the table.

These ions, which act as discrete units, are electrically charged molecules (a group of bonded atoms with an overall charge).

In solid form, an ionic compound is not electrically conductive because its ions are unable to flow (“electricity” is the flow of charged particles).

We use parentheses in a formula to indicate a group of atoms that behave as a unit.

Shades of gray exist between ionic and molecular compounds, and you’ll learn more about those later.

Look at the label or ingredients list on the various products that you use during the next few days, and see if you run into any of those in this table, or find other ionic compounds that you could now name or write as a formula.

The simplest name, “iron chloride,” will, in this case, be ambiguous, as it does not distinguish between these two compounds.

The settlement they won in 1996—$333 million—was the largest amount ever awarded for a direct-action lawsuit in the US at that time.

And H 2O is usually called water, not dihydrogen monoxide.

To name this correctly, “hydrogen” is omitted; the –ate of carbonate is replace with –ic ; and acid is added—so its name is carbonic acid.

Although no one has actually seen the inside of an atom, experiments have demonstrated much about atomic structure.

The nucleus contains protons and neutrons; its diameter is about 100,000 times smaller than that of the atom.

If the metal can form ions with different charges, a Roman numeral in parentheses follows the name of the metal to specify its charge.

Predict and test the behavior of α particles fired at a “plum pudding” model atom.

Select “Nature’s” mix of isotopes and compare it to your prediction.

The actual atomic mass of boron can vary from 10.807 to 10.819, depending on whether the mineral source is from Turkey or the United States.

Can you arrange these atoms to make a different molecule? If so, draw its structural formula and state its name.

The water in a swimming pool is a complex mixture of substances whose relative amounts must be carefully maintained to ensure the health and comfort of people using the pool.

We can argue that modern chemical science began when scientists started exploring the quantitative as well as the qualitative aspects of chemistry.

Even though a sodium cation has a slightly smaller mass than a sodium atom (since it is missing an electron), this difference will be offset by the fact that a chloride anion is slightly more massive than a chloride atom.

The mole provides a link between an easily measured macroscopic property, bulk mass, and an extremely important fundamental property, number of atoms, molecules, and so forth.

If the molecules were distributed equally among the roughly seven billion people on earth, each person would receive more than 100 billion molecules.

Copper wire is composed of many, many atoms of Cu.

These neurotransmitter molecules are stored in small intracellular structures called vesicles that fuse to the cell wall and then break open to release their contents when the neuron is appropriately stimulated.

Using miniaturized probes that can selectively detect dopamine molecules in very small amounts, scientists have determined that the vesicles of a certain type of mouse brain neuron contain an average of 30,000 dopamine molecules per vesicle.

The element nitrogen is the active ingredient for agricultural purposes, so the mass percentage of nitrogen in the compound is a practical and economic concern for consumers choosing among these fertilizers.

In this case, dividing by the smallest subscript still leaves us with a decimal subscript in the empirical formula.

The calculation is “most convenient” because, per the definition for percent composition, the mass of a given element in grams is numerically equivalent to the element’s mass percentage.

Nicotine, an alkaloid in the nightshade family of plants that is mainly responsible for the addictive nature of cigarettes, contains 74.02% C, 8.710% H, and 17.27% N.

The relative amount of oxygen in a planet’s atmosphere determines its ability to sustain aerobic life.

If we had not retained this guard digit, the final calculation for the mass of NaCl would have been 77.1 g, a difference of 0.3 g.

Since the dilution process does not change the amount of solute in the solution, n1 = n2.

Since the diluted concentration (0.12 M) is slightly more than one-fourth the original concentration (0.45 M), we would expect the volume of the diluted solution to be roughly four times the original concentration, or around 44 mL.

Use of these more detailed symbols can prevent confusion of mass percentages with other types of percentages, such as volume percentages.

The concentration of glucose in blood (commonly referred to as “blood sugar”) is also typically expressed in terms of a mass-volume ratio.

According to the EPA, when the concentration of lead in tap water reaches 15 ppb, certain remedial actions must be taken.

Due to the use of the same reference substance in defining the atomic mass unit and the mole, the formula mass (amu) and molar mass (g/mol) for any substance are numerically equivalent.

A 55-kg woman has 7.5 × 10−3 mol of hemoglobin (molar mass = 64,456 g/mol) in her blood.

The Cullinan diamond was the largest natural diamond ever found (January 25, 1905). It weighed 3104 carats (1 carat = 200 mg).

What does it mean when we say that a 200-mL sample and a 400-mL sample of a solution of salt have the same molarity?

The level of mercury in a stream was suspected to be above the minimum considered safe (1 part per billion by weight).

Igniting the mixture initiates a vigorous chemical reaction that rapidly generates large amounts of gaseous products.

Regardless of the absolute number of molecules involved, the ratios between numbers of molecules are the same as that given in the chemical equation.

Keep in mind, of course, that the formula subscripts define, in part, the identity of the substance, and so these cannot be changed without altering the qualitative meaning of the equation.

Explicitly representing all dissolved ions results in a complete ionic equation.

These spectator ions—ions whose presence is required to maintain charge neutrality—are neither chemically nor physically changed by the process.

These reactions are common in nature and are responsible for the formation of coral reefs in ocean waters and kidney stones in animals.

The solubility guidelines indicate all nitrate salts are soluble but that AgF is one of the exceptions to the general solubility of fluoride salts.

Weak acids are commonly encountered in nature, being the substances partly responsible for the tangy taste of citrus fruits, the stinging sensation of insect bites, and the unpleasant smells associated with body odor.

A double-arrow is appropriate in this equation because it indicates the HOCl is a weak acid that has not reacted completely.

The oxidation number (or oxidation state) of an element in a compound is the charge its atoms would possess if the compound was ionic.

Silver ions in solution are reduced to elemental silver at the surface of the copper wire, and the resulting Cu2+ions dissolve in the solution to yield a characteristic blue color.

It is a particularly interesting process, as it involves the same element, oxygen, undergoing both oxidation and reduction (a so-called disproportionation reaction).

The requirement of “charge balance” is just a specific type of “mass balance” in which the species in question are electrons.

The “equation” representing the preparation of pancakes per this recipe is 1 cup mix + 3/4 cup milk + 1 egg ⟶ 8 pancakes.

The effective operation of an airbag requires that it be rapidly inflated with an appropriate amount (volume) of gas when the vehicle is involved in a collision.

This reaction is very rapid, generating gaseous nitrogen that can deploy and fully inflate a typical airbag in a fraction of a second (~0.03–0.1 s).

Some products are difficult to collect without some loss, and so less than perfect recovery will reduce the actual yield.

Green chemistry is a philosophical approach that is being applied to many areas of science and technology, and its practice is summarized by guidelines known as the “Twelve Principles of Green Chemistry.”

The greater the weight of potassium carbonate added to reach the point where the bubbling ended, the more concentrated the vinegar.

Gravimetric methods were the first techniques used for quantitative chemical analysis, and they remain important tools in the modern chemistry laboratory.

The gaseous combustion products are swept through separate, preweighed collection devices containing compounds that selectively absorb each product.

vigorous redox reaction producing significant amounts of energy in the form of heat and, sometimes, light

Balanced equations are those whose coefficients result in equal numbers of atoms for each element in the reactants and products.

Combustion analysis is a gravimetric method used to determine the elemental composition of a compound by collecting and weighing the gaseous products of its combustion.

Colorful fireworks often involve the decomposition of barium nitrate and potassium chlorate and the reaction of the metals magnesium, aluminum, and iron with oxygen.

When heated to 700–800 °C, diamonds, which are pure carbon, are oxidized by atmospheric oxygen. (They burn!)

Lithium hydroxide may be used to absorb carbon dioxide in enclosed environments, such as manned spacecraft and submarines.

Silver is often extracted from ores as K[Ag(CN)2] and then recovered by the reaction 2K[Ag(CN)2](aq)+Zn(s) ⟶ 2Ag(s)+Zn(CN)2(aq)+2KCN(aq).

Automotive air bags inflate when a sample of sodium azide, NaN 3, is very rapidly decomposed.

Freon-12 has been banned and is no longer used as a refrigerant because it catalyzes the decomposition of ozone and has a very long lifetime in the atmosphere.

Potatoes can be peeled commercially by soaking them in a 3-M to 6-M solution of sodium hydroxide, then removing the loosened skins by spraying them with water.

Sliding a match head along a rough surface initiates a combustion reaction that produces energy in the form of heat and light.

Every day, the sun provides the earth with almost 10,000 times the amount of energy necessary to meet all of the world’s energy needs for that day.

The total quantity of matter and energy in the universe is fixed.

Heat flow will continue until the two substances are at the same temperature.

The sparks are tiny bits of the molten metal flying away.

Note that specific heat is measured in units of energy per temperature per mass and is an intensive property, being derived from a ratio of two extensive properties (heat and mass).

After the sun goes down, the molten salt mixture can then release enough of its stored heat to produce steam to run the turbines for 6 hours.

Its 170,000 mirrors focus huge amounts of sunlight on three water-filled towers, producing steam at over 538 °C that drives electricity-producing turbines.

The magnitude of the heat (change) is therefore the same for both substances, and the negative sign merely shows that qsubstance M and qsubstance W are opposite in direction of heat flow.

However, the observation that the metal is silver/gray in addition to the value for the specific heat indicates that the metal is lead.

Bending the disk creates nucleation sites around which the metastable NaC2H3O2 quickly crystallizes.

When the bag of water is broken, the pack becomes cold because the dissolution of ammonium nitrate is an endothermic process that removes thermal energy from the water.

The term “bomb” comes from the observation that these reactions can be vigorous enough to resemble explosions that would damage other calorimeters.

The pellet is burned inside a bomb calorimeter, and the measured temperature change is converted into energy per gram of food.

Substances act as reservoirs of energy, meaning that energy can be added to them or removed from them.

If you stand on the summit of Mt. Kilimanjaro, you are at an altitude of 5895 m, and it does not matter whether you hiked there or parachuted there.

A process that is endothermic in one direction is exothermic in the opposite direction.

Standard enthalpy of combustion (ΔHC°)is the enthalpy change when 1 mole of a substance burns (combines vigorously with oxygen) under standard state conditions.

The combustion of 1.00 L of isooctane produces 33,100 kJ of heat. (This amount of energy is enough to melt 99.2 kg, or about 218 lbs, of ice.)

These values are especially useful for computing or predicting enthalpy changes for chemical reactions that are impractical or dangerous to carry out.

Enthalpy changes depend only on where a chemical process starts and ends, but not on the path it takes from start to finish.

It shows how we can find many standard enthalpies of formation (and other values of ΔH) if they are difficult to determine experimentally.

The stepwise reactions we consider are: (i) decompositions of the reactants into their component elements, followed by (ii) re-combinations of the elements to give the products.

property depending only on the state of a system, and not the path taken to reach that state

A burning match and a bonfire may have the same temperature, yet you would not sit around a burning match on a fall evening to stay warm.

When asked which sample of water lost the most heat, one student replied that both bottles lost the same amount of heat because they started at the same temperature and finished at the same temperature.

The first time a student solved this problem she got an answer of 88 °C. Explain why this is clearly an incorrect answer.

Which is the least expensive source of energy in kilojoules per dollar: a box of breakfast cereal that weighs 32 ounces and costs $4.23, or a liter of isooctane that costs $0.45?

Joseph Priestly prepared oxygen in 1774 by heating red mercury(II) oxide with sunlight focused through a lens.

Though no longer used as auto headlamps, acetylene is still used as a source of light by some cave explorers.

Assuming that an automobile’s mileage is directly proportional to the heat of combustion of the fuel, calculate how much farther an automobile could be expected to travel on 1 L of gasoline than on 1 L of ethanol.

Measurements of the emitted light wavelengths enabled astronomers to identify the elements in the nebula, determining that it contains specific ions including S+ and O2+.

While this wave can quickly encircle a large stadium in a few seconds, none of the fans actually travel with the wave-they all stay in or above their seats.

Waves need not be restricted to travel through matter.

Increasingly, cell towers are designed to blend in with the landscape, as with the Tucson, Arizona, cell tower disguised as a palm tree.

The spacing of the fringes depends on the wavelength, with the fringes being more closely spaced for the shorter-wavelength blue light.

This is an example of quantization, in which only discrete values from a more general set of continuous values of some property are observed.

Because of the circular symmetry of the drum surface, its boundary conditions result in two types of nodes: radial nodes that sweep out all angles at constant radii and, thus, are seen as circles about the center, and angular nodes that sweep out all radii at constant angles.

Not only did the theoretical curves not show a peak, they absurdly showed the intensity becoming infinitely large as the wavelength became smaller, which would imply that everyday objects at room temperature should be emitting large amounts of UV light.

Somehow, at a deep fundamental level still not fully understood, light is both wavelike and particle-like.

Only energy, not the number or amplitude, of the photons influences the kinetic energy of the electrons.

The origin of discrete spectra in atoms and molecules was extremely puzzling to scientists in the late nineteenth century, since according to classical electromagnetic theory, only continuous spectra should be observed.

That such a simple formula as the Rydberg formula could account for such precise measurements seemed astounding at the time.

This loss in orbital energy should result in the electron’s orbit getting continually smaller until it spirals into the nucleus, implying that atoms are inherently unstable.

Since the Rydberg constant was one of the most precisely measured constants at that time, this level of agreement was astonishing and meant that Bohr’s model was taken seriously, despite the many assumptions that Bohr needed to derive it.

Bohr’s model was severely flawed, since it was still based on the classical mechanics notion of precise orbits, a concept that was later found to be untenable in the microscopic domain.

Why did the model work so well describing hydrogen and one-electron ions, but could not correctly predict the emission spectrum for helium or any larger atoms?

The unquestionable separation of waves and particles was no longer the case for the microscopic world.

Initially, when only a few electrons have been recorded, they show clear particle-like behavior, having arrived in small localized packets that appear to be random.

Heisenberg’s uncertainty principle implies that such a view is untenable in the microscopic domain and that there are fundamental limitations governing the motion of quantum particles.

Quantization in Schrödinger’s theory was a natural consequence of the underlying mathematics of the wave equation.

It is said that the energy of an electron in an atom is quantized, that is, it can be equal only to certain specific values and can jump from one energy level to another but not transition smoothly or stay between these levels.

An atomic orbital, which is distinct from an orbit, is a general region in an atom within which an electron is most probable to reside.

The electron spin is a different kind of property. It is a completely quantum phenomenon with no analogues in the classical realm.

An electron acts like a tiny magnet.

The specific arrangement of electrons in orbitals of an atom determines many of the chemical properties of that atom.

Thus, many students find it confusing that, for example, the 5p orbitals fill immediately after the 4d, and immediately before the 6s.

This procedure is called the Aufbau principle, from the German word Aufbau (“to build up”).

The orbitals are filled as described by Hund’s rule: the lowest-energy configuration for an atom with electrons within a set of degenerate orbitals is that having the maximum number of unpaired electrons.

As discussed previously, the 3d orbital with no radial nodes is higher in energy because it is less penetrating and more shielded from the nucleus than the 4s, which has three radial nodes.

In the case of Cr and Cu, we find that half-filled and completely filled subshells apparently represent conditions of preferred stability.

The similarity in chemical properties among elements of the same group occurs because they have the same number of valence electrons.

For transition metals and inner transition metals, however, electrons in the s orbital are easier to remove than the d or f electrons.

This might seem counterintuitive because it implies that atoms with more electrons have a smaller atomic radius.

The transition elements, on the other hand, lose the ns electrons before they begin to lose the (n – 1)d electrons, even though the ns electrons are added first, according to the Aufbau principle.

Energy is always required to remove electrons from atoms or ions, so ionization processes are endothermic and IE values are always positive.

This jump corresponds to removal of the core electrons, which are harder to remove than the valence electrons.

The reduction of the EA of the first member can be attributed to the small size of the n= 2 shell and the resulting large electron–electron repulsions.

The uncertainty principle is a consequence of quantum particles exhibiting wave–particle duality.

wave-particle duality: term used to describe the fact that elementary particles including matter exhibit properties of both particles (including localized position, momentum) and waves (including nonlocalization, wavelength, frequency)

That light demonstrates both wavelike and particle-like behavior is known as wave-particle duality.

The quantum mechanical model of atoms describes the three-dimensional position of the electron in a probabilistic manner according to a mathematical function called a wavefunction.

The eyes of certain reptiles pass a single visual signal to the brain when the visual receptors are struck by photons of a wavelength of 850 nm.

What does it mean to say that the energy of the electrons in an atom is quantized?

How many electrons could be held in the second shell of an atom if the spin quantum number ms could have three values instead of just two?

Thallium was used as a poison in the Agatha Christie mystery story “The Pale Horse.”

These molecules have single and double carbon-carbon bonds arranged to form a geometric framework of hexagons and pentagons, similar to the pattern on a soccer ball.

Chlorine is poisonous, but sodium chloride is essential to life; sodium atoms react vigorously with water, but sodium chloride simply dissolves in water.

It is incorrect to refer to a sodium chloride (NaCl) “molecule” because there is not a single ionic bond, per se, between any specific pair of sodium and chloride ions.

The formation of these 1+, 2+, and 3+ cations is ascribed to the inert pair effect, which reflects the relatively low energy of the valence s-electron pair for atoms of the heavy elements.

The strong attraction of each shared electron to both nuclei stabilizes the system, and the potential energy decreases as the bond distance decreases.

This unequal distribution of electrons is known as a polar covalent bond, characterized by a partial positive charge on one atom and a partial negative charge on the other.

Linus Pauling, shown in Figure 7.7 , is the only person to have received two unshared (individual) Nobel Prizes: one for chemistry in 1954 for his work on the nature of chemical bonds and one for peace in 1962 for his opposition to weapons of mass destruction.

The degree to which electrons are shared between atoms varies from completely equal (pure covalent bonding) to not at all (ionic bonding).

The tendency of main group atoms to form enough bonds to obtain eight valence electrons is known as the octet rule.

Rearrange the electrons of the outer atoms to make multiple bonds with the central atom in order to obtain octets wherever possible.

An exception is that hydrogen is almost never a central atom. As the most electronegative element, fluorine also cannot be a central atom.

Upon his death in 2005, the US Senate honored him as the “Father of Nanotechnology.”

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.

Formal charge is only a useful bookkeeping procedure; it does not indicate the presence of actual charges.

A double bond between two atoms is shorter (and stronger) than a single bond between the same two atoms.

A medieval traveler, having never before seen a rhinoceros, described it as a hybrid of a dragon and a unicorn because it had many properties in common with both.

Although the four C–H bonds are equivalent in the original molecule, they do not each require the same energy to break; once the first bond is broken (which requires 439 kJ/mol), the remaining bonds are easier to break.

Because D values are typically averages for one type of bond in many different molecules, this calculation provides a rough estimate, not an exact value, for the enthalpy of reaction.

Thus, the lattice energy of an ionic crystal increases rapidly as the charges of the ions increase and the sizes of the ions decrease.

For ionic compounds, lattice energies are associated with many interactions, as cations and anions pack together in an extended lattice.

The VSEPR model assumes that electron pairs in the valence shell of a central atom will adopt an arrangement that minimizes repulsions between these electron pairs by maximizing the distance between them.

The actual bond angles deviate slightly from the idealized angles because the lone pair takes up a larger region of space than do the single bonds.

The H–N–H bond angles in NH 3are slightly smaller than the 109.5° angle in a regular tetrahedron because the lone pair-bonding pair repulsion is greater than the bonding pair-bonding pair repulsion.

In a trigonal bipyramidal electron-pair geometry, lone pairs always occupy equatorial positions because these more spacious positions can more easily accommodate the larger lone pairs.

The next several examples illustrate the effect of lone pairs of electrons on molecular structure.

To minimize lone pair repulsions, the lone pair occupies one of the equatorial positions.

This separation of charge gives rise to a bond dipole moment.

Each of the bonds is polar, but the molecule as a whole is nonpolar.

In this case, however, the molecular structure is bent because of the lone pairs on O, and the two bond moments do not cancel.

The bond moments will be maximized when the electronegativity difference is greatest.

theory used to predict the bond angles in a molecule based on positioning regions of high electron density as far apart as possible to minimize electrostatic repulsion

The actual distribution of electrons (the resonance hybrid) is an average of the distribution indicated by the individual Lewis structures (the resonance forms).

Why is it incorrect to speak of a molecule of solid NaCl?

Correct the following statement: “The bonds in solid PbCl 2are ionic; the bond in a HCl molecule is covalent. Thus, all of the valence electrons in PbCl 2are located on the Cl–ions, and all of the valence electrons in a HCl molecule are shared between the H and Cl atoms.”

Based on formal charge considerations, which of the following would likely be the correct arrangement of atoms in nitrosyl chloride: ClNO or ClON?

When a molecule can form two different structures, the structure with the stronger bonds is usually the more stable form.

Explain how a molecule that contains polar bonds can be nonpolar.

Draw them and discuss how measurements of dipole moments could help distinguish among them.

We can pour liquid nitrogen through a magnetic field with no visible interactions, while liquid oxygen is attracted to the magnet and floats in the magnetic field.

At some specific distance between the atoms, which varies depending on the atoms involved, the energy reaches its lowest (most stable) value.

In a π bond, the regions of orbital overlap lie on opposite sides of the internuclear axis. Along the axis itself, there is a node, that is, a plane with no probability of finding an electron.

In a σ bond, there is a greater degree of orbital overlap than in a π bond.

The prediction of the valence bond theory model does not match the real-world observations of a water molecule; a different model is needed.

Hybrid orbitals do not exist in isolated atoms. They are formed only in covalently bonded atoms.

Although quantum mechanics yields the “plump” orbital lobes as depicted in Figure 8.10, sometimes for clarity these orbitals are drawn thinner and without the minor lobes.

Experimental evidence shows that rotation around σ bonds occurs easily.

These hybridizations are only possible for atoms that have d orbitals in their valence subshells (that is, not those in the first or second period).

It is important to remember that hybridization was devised to rationalize experimentally observed molecular geometries.

This unhybridized p orbital is perpendicular to the plane of the sp2 hybrid orbitals.

Rotation about the internuclear axis is much more difficult for multiple bonds; however, this would drastically alter the off-axis overlap of the π bonding orbitals, essentially breaking the π bond.

The electrons in the π bonds are not located in one set of p orbitals or the other, but rather delocalized throughout the molecule.

If you place a frog near a sufficiently large magnet, it will levitate.

The asterisk signifies that the orbital is an antibonding orbital.

When orbital lobes of the same phase overlap, constructive wave interference increases the electron density.

He was born in Austria, and during World War II he was part of the Kindertransport program that rescued 10,000 children from the Nazi regime.

The bond order is calculated by subtracting the destabilizing (antibonding) electrons from the stabilizing (bonding) electrons.

The net energy change would be zero, so there is no driving force for helium atoms to form the diatomic molecule.

s-p mixing does not create new orbitals; it merely influences the energies of the existing molecular orbitals.

The presence of two unpaired electrons has proved to be difficult to explain using Lewis structures, but the molecular orbital theory explains it quite well.

The allowed energy levels for all the bonding orbitals are so close together that they form a band, called the valence band.

Oxygen's paramagnetism is explained by the presence of two unpaired electrons in the (π 2py, π2pz)* molecular orbitals.

When the orbitals overlap along an axis containing the nuclei, they form a σ bond. When they overlap in a fashion that creates a node along this axis, they form a π bond.

Correctly predicting the magnetic properties of molecules is in advantage of molecular orbital theory over Lewis structures and valence bond theory.

A mixture of xenon and fluorine gases, confined in a quartz bulb and placed on a windowsill, is found to slowly produce a white solid.

Can a molecule with an even number of electrons ever be paramagnetic? Explain why or why not.

The atmosphere above us exerts a large pressure on objects at the surface of the earth, roughly equal to the weight of a bowling ball pressing on an area the size of a human thumbnail.

At sea level, this pressure is roughly the same as that exerted by a full-grown African elephant standing on a doormat, or a typical bowling ball resting on your thumbnail.

Using very dense liquid mercury permits the construction of reasonably sized barometers, whereas using water would require a barometer more than 30 feet tall.

The pressure of the gas equals the hydrostatic pressure due to a column of mercury of height 13.7 cm plus the pressure of the atmosphere at sea level.

When the cuff’s pressure equals the arterial systolic pressure, blood flows past the cuff, creating audible sounds that can be heard using a stethoscope.

The troposphere (up to 12 km above sea level, roughly 80% of the earth’s atmosphere by mass and the layer where most weather events originate).

When the hydrogen-filled balloon depicted in (a) landed, the frightened villagers of Gonesse reportedly destroyed it with pitchforks and knives.

High temperature could lead to high pressure, causing the can to burst.

If we slowly push in the plunger while keeping temperature constant, the gas in the syringe is compressed into a smaller volume and its pressure increases; if we pull out the plunger, the volume increases and the pressure decreases.

You then breathe in and out again, and again, repeating this Boyle’s law cycle for the rest of your life.

An ideal gas is a hypothetical construct that may be used along with kinetic molecular theory to effectively explain the gas laws.

It would require 1020 L (269 gal) of gaseous methane at about 1 atm of pressure to replace 1 gal of gasoline.

The diver must vent air from the BCD or risk an uncontrolled ascent that could rupture the lungs.

It took the mob only a moment to remove his head; a century will not suffice to reproduce it.

Removing the flask from heat at the instant when the last bit of liquid becomes gas, at which time the flask will be filled with only gaseous sample at ambient pressure.

The gases behave independently, so the partial pressure of each gas can be determined from the ideal gas equation.

As a gas is collected over water, it becomes saturated with water vapor and the total pressure of the mixture equals the partial pressure of the gas plus the partial pressure of the water vapor.

Gases combine, or react, in definite and simple proportions by volume, provided that all gas volumes are measured at the same temperature and pressure.

The thin skin of our atmosphere keeps the earth from being an ice planet and makes it habitable.

If you have ever been in a room when a piping hot pizza was delivered, you have been made aware of the fact that gaseous molecules can quickly spread throughout a room, as evidenced by the pleasant aroma that soon reaches your nose.

A balloon filled with helium (the green one) partially deflates because the smaller, light helium atoms effuse through small holes in the rubber much more readily than the heavier molecules of nitrogen and oxygen found in air.

The small difference in molecular weights between 235UF6 and 238UF6 only about 0.4% enrichment, is achieved in one diffuser.

A current hot political issue is how to deny this technology to Iran, to prevent it from producing enough enriched uranium for them to use to make nuclear weapons.

In a gas sample, individual molecules have widely varying speeds; however, because of the vast number of molecules and collisions involved, the molecular speed distribution and average speed are constant.

The molecular speed distribution for nitrogen gas (N2) shifts to the right and flattens as the temperature increases; it shifts to the left and heightens as the temperature decreases.

Ideal gas behavior is therefore indicated when this ratio is equal to 1, and any deviation from 1 is an indication of non-ideal behavior.

This change is more pronounced at low temperatures because the molecules have lower KE relative to the attractive forces, and so they are less effective in overcoming these attractions after colliding with one another.

At some intermediate pressure, the two corrections have opposing influences and the gas appears to follow the relationship given by PV = nRT over a small range of pressures.

The van der Waals equation is a modified version of the ideal gas equation containing additional terms to account for non-ideal gas behavior.

The theory assumes that gases consist of widely separated molecules of negligible volume that are in constant motion, colliding elastically with one another and the walls of their container.

Why should you roll or belly-crawl rather than walk across a thinly-frozen pond?

If the can is thrown into a fire (T = 475 °C), what will be the pressure in the hot can?

A balloon that is 100.21 L at 21 °C and 0.981 atm is released and just barely clears the top of Mount Crumpet in British Columbia.

Cavendish prepared hydrogen in 1766 by the novel method of passing steam through a red-hot gun barrel.

A balloon filled with helium gas is found to take 6 hours to deflate to 50% of its original volume.

The lifting capacity of a hot air balloon is equal to the difference in the mass of the cool air displaced by the balloon and the mass of the gas in the balloon.

In the liquid and solid states, these interactions are of considerable strength and play an important role in determining a number of physical properties that do depend on the chemical identity of the substance.

These forces serve to hold particles close together, whereas the particles’ KE provides the energy required to overcome the attractive forces and thus increase the distance between particles.

However, to break the covalent bonds between the hydrogen and chlorine atoms in one mole of HCl requires about 25 times more energy—430 kilojoules.

A molecule that has a charge cloud that is easily distorted is said to be very polarizable and will have large dispersion forces.

Although dispersion forces are very weak, the total attraction over millions of spatulae is large enough to support many times the gecko’s weight.

By changing how the spatulae contact the surface, geckos can turn their stickiness “on” and “off.”

The stark contrast between our naïve predictions and reality provides compelling evidence for the strength of hydrogen bonding.

Importantly, the two strands of DNA can relatively easily “unzip” down the middle since hydrogen bonds are relatively weak compared to the covalent bonds that hold the atoms of the individual DNA molecules together.

As a result of this high surface tension, the surface of water represents a relatively “tough skin” that can withstand considerable force without breaking.

Mercury therefore does not wet glass, and it forms a convex meniscus when confined in a tube because the cohesive forces within the mercury tend to draw it into a drop.

You depend on a constant supply of tears to keep your eyes lubricated and on capillary action to pump tear fluid away.

This procedure can be easily done because of capillary action, the ability of a liquid to flow up a small tube against gravity.

Keep in mind that this is not a static situation, as molecules are continually exchanged between the condensed and gaseous phases.

The boiling point of a liquid is the temperature at which its equilibrium vapor pressure is equal to the pressure exerted on the liquid by its gaseous surroundings.

Note that the pressure can be in any units, so long as they agree for both P values, but the temperature must be in kelvin for the Clausius-Clapeyron equation to be valid.

At this point, the temperature of the solid stops rising, despite the continual input of heat, and it remains constant until all of the solid is melted.

When solid iodine is warmed, the solid sublimes and a vivid purple vapor forms.

If the burner setting is increased to provide heat at a greater rate, the water temperature does not rise, but instead the boiling becomes more vigorous (rapid).

A phase diagram combines plots of pressure versus temperature for the liquid-gas, solid-liquid, and solid-gas phase-transition equilibria of a substance.

Water is an unusual substance in this regard, as most substances exhibit an increase in melting point with increasing pressure.

At pressures lower than the triple point, water cannot exist as a liquid, regardless of the temperature.

All of the water in the container is now present in a single phase whose physical properties are intermediate between those of the gaseous and liquid states.

Like a gas, it penetrates deep into the coffee beans; like a liquid, it effectively dissolves certain substances.