WHAT IS CHEMISTRY from chem and phy for NA.docx

WHAT IS CHEMISTRY? Chemistry is the study of matter and the changes it undergoes. Every aspect of your patients’ physiology is a proper study of chemistry. Even such abstract processes as thought and emotion are believed to be based on biochemical processes in the brain. Therefore, it is appropriate...

WHAT IS CHEMISTRY? Chemistry is the study of matter and the changes it undergoes. Every aspect of your patients’ physiology is a proper study of chemistry. Even such abstract processes as thought and emotion are believed to be based on biochemical processes in the brain. Therefore, it is appropriate that we review some essential concepts upon which chemistry is founded. Chemistry is a vast and complex field, so don’t fall into the common trap of believing you know nothing about chemistry because you don’t know everything about chemistry. Generally, even PhD-level chemists are considered to be experts in only one or two of the five classic areas of chemistry. Analytical chemists study the composition of samples, both in terms of what is present in the sample, and the percent composition of each component. Physical chemists strive to discern models needed to understand chemical systems from a theoretical framework. Inorganic chemists study substances that are derived from all elements except carbon. Organic chemists study compounds based on carbon, while biochemists study the chemistry that occurs in living systems. In its common use, the term organic connotes derivation from natural (and presumably) healthy sources, but this is not how chemists understand the term. Virtually all of the substances studied by biochemists are organic compounds, while a huge number of organic compounds are synthetic and not found in living systems. There are also several cross-disciplinary areas of chemistry, including nuclear chemistry, polymer chemistry, nanochemistry, and material sciences. You no doubt took one (or more) chemistry courses as a part of your undergraduate studies in nursing. In this chapter, we review some of the basics of chemistry that you might have gotten rusty on. Your previous experience with chemistry notwithstanding, chemistry is not just an applied algebra course. Many of the essential chemistry concepts are not quintessentially mathematical in nature. In fact, it is sometimes more useful to gain an understanding of these ideas at a qualitative level. Therefore, we focus on conceptual and holistic topics. The major goal of this chapter is for you to correctly and precisely use the language of chemistry. Matter Chemistry studies matter. Let’s consider further what that means and the kinds of matter that exist. Matter is formally defined as anything that has mass and occupies space. Matter doesn’t have to be visible. For example, air and nitrous oxide are matter. While you might argue that you can see light, light is not considered to be matter because it does not have mass. Atoms are the basic building blocks of matter, so under ordinary conditions of temperature and pressure, essentially all matter is comprised of atoms.1 Sometimes atoms join to form molecules. An element contains only a single kind of atom, whereas compounds contain two or more kinds of atoms. Descriptions for these terms are given in the following. Atoms are the fundamental building blocks of matter. Atoms themselves are comprised of three simpler particles: protons, neutrons, and electrons. Protons are positively charged and have a mass of approximately 1 atomic mass unit (amu). One amu is equal to 1.66 × 10−27 kg. The number of protons, also called the atomic number (Z), determines the identity of the atom. Neutrons are electrically neutral and have a mass of approximately 1 amu. Electrons are negatively charged and have a much, much smaller mass than either protons or neutrons. Chemists typically ignore the mass of an electron. Ions are atoms or a group of atoms bonded together that have a net electrical charge. This charge is attained by adding or removing electrons. Cations have a positive electrical charge. Anions have a negative electrical charge. Elements are comprised of only one kind of atom. Compounds are comprised of more than one kind of atom in a fixed ratio by mass. Molecules (or molecular compounds) are a group of atoms chemically bonded together into a discrete unit by covalent bonds. Molecules are electrically neutral. Ionic compounds contain positively charged ions and negatively charged ions. There are no identifiable discrete units in an ionic compound. All positively charged ions are attracted to all of the negatively charged ions (and vice versa). Therefore, ionic compounds are not molecules. imagesQuestion: Can a substance be both a molecule and an element? Answer: Yes. Oxygen (O2) consists of two oxygen atoms bonded together to form an oxygen molecule. But oxygen is also an element, because it contains only oxygen atoms. Physical and Chemical Properties and Changes Chemistry also studies the properties of matter, as well as the changes that matter undergoes. There are two categories of change. Physical changes occur without changing the chemical makeup of the substance undergoing the changes. Chemical changes always result in the formation of chemically different substances. When an ice cube melts, it changes from water in the solid form into water in the liquid form. However, it is still water. Therefore, melting is an example of a physical change. If we run an electric current through water (containing a small amount of an electrolyte, such as sodium sulfate), the water will break down into hydrogen gas and oxygen gas. We started with one chemical substance, water, and ended up with new chemical substances, hydrogen and oxygen. This is an example of a chemical change. A physical property can be observed or measured without changing the chemical makeup of the substance. Physical properties fall into two categories. An intensive physical property is integral to the material, regardless of how much material is there. Color is a good example of an intensive physical property. Extensive physical properties depend on the sample size. Volume and mass are good examples of extensive physical properties. A chemical property describes the type of chemical changes the material tends to undergo. For example, a chemical property of some anesthetic gases is that they are flammable. Pure Substances and Mixtures Pure substances are materials that cannot be physically separated into simpler components. The chemical and physical properties of a substance are uniform through all samples of that substance. A substance can be either a compound or an element. If the substance is a compound, it can be chemically separated into its elemental components. Mixtures are comprised of two or more pure substances. Mixtures can be resolved into simpler components through physical processes. Homogeneous mixtures are uniform in chemical and physical properties throughout the sample. Normal saline (like all solutions) is an example of a homogenous mixture. Air is another good example of a homogeneous mixture. A heterogeneous mixture exhibits distinct phase boundaries between its components. A phase boundary is a demarcation where the chemical and/or physical properties of the sample change. Emesis is one example of a heterogeneous mixture. The relationships between the various kinds of matter are summarized in Figure 2.1. images Figure 2.1 Kinds of Matter images ATOMIC STRUCTURE AND DIMENSION Atoms are incredibly small. As you already know, the protons and neutrons are bound together by the strong nuclear force into an incredibly dense structure called the nucleus at the center of the atom. This strong nuclear force results from conversion of a part of the proton and neutron mass into energy, according to the famous Einstein relationship E = mc2. Electrons are bound to the nucleus by the electromagnetic force (attraction of opposite charges). However, you should abandon the “solar system” picture of electrons orbiting the nucleus in well-defined paths, like the planets revolve around the sun. Electrons surround the nucleus in a nebulous cloud that is described by quantum-mechanical rules. When dealing with quantities on the atomic scale, everyday, common-sense concepts like determinism (if a is true, then b must be true) and geometry no longer apply. We are forced to adopt quantum mechanical models that give us only probabilities as to where we are likely to find the electrons. Furthermore, subatomic “particles” behave as point-localized particles when an observer interacts with them in a manner that predicts they will be point-localized particles. Absent an observer, protons, neutrons, and electrons can be described only by wave-like probability functions, whose energy and momentum emerge by application of an appropriate mathematical operator. Wave–particle duality and uncertainty are the heart of quantum theory and underlie the stark contrast between the world at the atomic scale and our everyday experiences. Atomic radii are on the order of 100 pm (picometers) (100 × 10−12 m = 10−10 m), whereas the radius of an atomic nucleus is on the order of femtometers (10−15 m). Thus, to a first approximation, the nucleus of an atom is about 100,000 times smaller than the atom. In terms of volume, the volume of the nucleus is smaller than that of the atom by a factor of about 1 × 1015. Atomic Number and Mass Number All atoms contain protons and electrons. With the exception of ordinary hydrogen, all atoms contain neutrons. The atomic number (Z) of an atom is the number of protons in the nucleus. The identity of an atom is determined exclusively by the atomic number. For example, carbon has atomic number 6. All carbon atoms have six protons, and all atoms having six protons are carbon atoms. The neutron number (N) is the number of neutrons in the nucleus. The mass number (A) of an atom, is the sum of the atomic number (or proton number) and the neutron number, is an integer. The unit for atomic mass is the amu. One amu is defined to be exactly 1/12 the mass of one 12C atom. Protons and neutrons each have a mass of about 1 amu. In more precise terms, neutrons have a mass of 1.0087 amu or 1.6749 × 10−27 kg. Protons have a mass of 1.0073 amu or 1.6726 × 10−27 kg. When protons and neutrons combine to form an atomic nucleus, there is a mass deficit, because some of the mass is converted into a binding energy. In other words, the mass of the nucleus is slightly less than the sum of the individual masses of the protons and neutrons. However, for our purpose, it is adequate to consider the masses of the proton and neutron to be equal and to ignore the mass deficit. You can easily tell the atomic number from the mass number, because the mass number can never be smaller than the atomic number. The mass number is frequently written as a superscript and the atomic number as a subscript (images Atomic Symbol). Sometimes, the element name is simply followed by the mass number. Technetium-99 images is used as a radioactive tracer in nuclear medicine. How many protons and neutrons does an atom of this material have? The atomic number (the smaller of the two numbers) is 43. Therefore, a technetium atom has 43 protons. The mass number is 99. The mass number is equal to the sum of the number of protons plus the number of neutrons. Therefore, if we subtract the atomic number from the mass number, we find the number of neutrons. In this case, the neutron number is 99 − 43 = 56. Elements are always electrically neutral, and therefore, each atom must have an equal number of positively charged protons and negatively charged electrons. The number of electrons is equal to the number of protons in an electrically neutral atom. To emphasize the importance of electrical neutrality, imagine a sample of graphite (elemental carbon) with a mass of 1 g. That is about the amount of graphite in a pencil. Carbon is element number 6, and each carbon atom has six protons as well as six electrons. If each carbon atom were missing one electron, the amount of charge on this quantity of carbon ions would amount to about 8,000 C (coulombs) of charge.2 You might not be familiar with coulombs as a quantity of charge, but consider that an average lightning bolt has somewhere between 5 and 20 C of charge. Isotopes and Mass Spectroscopy In a modern laboratory, it is possible to determine the mass of an atom or molecule using a mass spectrometer. Figure 2.2 illustrates how a mass spectrometer works. The sample (A) is introduced into the instrument. The injection port is maintained under conditions of high temperature and low pressure, which causes the sample to (at least partially) vaporize into the gas phase. The sample diffuses into the ionization sector. Here the sample is bombarded with high-energy electrons (an “electron gun”), and this electronic attack knocks one electron off of A. Removing a negatively charged electron from an electrically neutral particle affects the introduction of a positive charge onto A, and this gives a molecular ion A+. It is necessary to place a charge onto the sample because, at the molecular level, it is very difficult to manipulate electrically neutral particles. Charged particles, however, are easy to manipulate. First, they are attracted by oppositely charged particles. The acceleration sector consists of a series of charged metal plates. The molecular ion is attracted to the negatively charged plates and repelled by the positively charged plates. This series of pushes and pulls accelerates the molecular ion, and sends it hurtling into the magnetic sector. images Figure 2.2 Schematic Diagram of Mass Spectrometer A very useful property of charged particles is that, once they are moving, they behave like little magnets. These little magnets can be given a push or a pull by other magnets. In the magnetic sector, external magnets are arranged so as to push the molecular ion in a curved path. The amount of curvature in the molecular ion’s path depends on the mass of the molecular ion.3. If the molecular ion is too light or too heavy, the ion is either deflected too much or too little and crashes into the wall. Only ions of the correct mass curve around the bend and reach the detector. By manipulating the strength of the external magnets, you can scan to find the atomic (or molecular) mass of the sample. The mass spectrometer was developed by J. J. Thompson. In obtaining the mass spectrum of neon, he found a large signal at 20 amu, but also a small signal at 22 amu. He first assumed it was an impurity. So, he kept repeating the experiment, each time more and more carefully purifying the sample, but the small signal at 22 amu remained constant. What Thompson discovered was the existence of isotopes. Isotopes have the same atomic number but a different mass number (same Z, different A), or the same number of protons and a different number of neutrons. The discovery of isotopes illustrates an important characteristic of a good scientist and, by extension, a good clinician. Many students, when confronted with unexpected information that does not conform to a predicted model, are usually tempted to ignore that information. They will assume that the instrument was not working properly, or that the experiment was flawed, or that they made an error. You should always be cognizant of this fact. Many important scientific discoveries were made when experimental data was obtained that did not conform to an initial hypothesis. Of course, good science requires replication of the measurement by a variety of experiments in order to validate that the unexpected result is reproducible. When you encounter unexpected results, don’t be afraid to consider the possibility that you have encountered something really new and that existing theories might have to be modified, expanded, or even discarded in order to accommodate new information. images DALTON'S ATOMIC THEORY The idea that all matter is made of atoms is a familiar concept that can be recited by the average first grader. However, the general acceptance of the atomic theory dates to the early part of the 20th century, when Albert Einstein published a paper explaining Brownian motion. The notion of atoms dates back to ancient times, but these models are largely based on philosophical arguments, rather than empirical evidence. John Dalton first formulated an atomic theory in the early 19th century that was founded on experimental evidence. The postulates of Dalton’s atomic theory include the following: 1.Elements are composed of tiny, indivisible particles called atoms. All atoms of a given element are identical and unique to that element. 2.Compounds are formed by bonding atoms together in a fixed ratio. 3.Chemical reactions do not create, destroy, or change atoms into atoms of other elements. Chemical reactions cause atoms to recombine into new substances. Dalton based his theory on two important laws: the law of conservation of mass and the law of definite proportions. Antoine Lavoisier proposed the law of conservation of mass at the end of the 18th century. This law observes that no detectable change in the total mass occurs during a chemical reaction. In other words, during a chemical change, the components of a system are neither created nor destroyed. They simply recombine into new substances. Another French chemist, Joseph Proust, proposed the law of definite proportions, which states that different samples of a pure compound always contain the same elements in the same proportion by mass. For example, a sample of water taken from any source always contains 11.2% hydrogen and 88.8% oxygen by mass. Dalton discerned a third law, the law of multiple proportions. Some elements can combine to give more than one compound. For example, carbon can burn in oxygen to give carbon dioxide as well as carbon monoxide. Likewise, nitrogen and oxygen combine to give several oxides, including nitrous oxide (N2O, an anesthetic gas) and nitrogen dioxide (NO2, a component of air pollution). The ratio of the weights of the elements in these compounds is always a ratio of small, whole numbers, which supports the notion that the elements must be delivered as particles (i.e., atoms) rather than a continuous substance. Dalton’s atomic theory was an important milestone in the development of chemistry, but modern chemistry students will correctly note that it was incomplete, and in some cases just plainly wrong. For example, not all atoms of a given element are identical, because Dalton did not know about the existence of isotopes. Likewise, we now know that atoms are comprised of still smaller particles and that nuclear processes convert atoms of one element into atoms of other elements. By the very nature of science, when a hypothesis, law, or model—no matter how dearly held—fails to make correct predictions, it must be discarded or modified. So, significant portions of Dalton’s original theory have been modified. However, the importance of Dalton’s theory can hardly be understated and should not be assessed by whether or not it was correct in the finest details, but in how it provided a working foundation that guided current and future scientists in their quest to understand the physical world. images THE PERIODIC TABLE OF THE ELEMENTS One of the most important achievements of 19th-century chemists was recognizing that the chemical and physical properties of the known elements repeat in a regular or periodic fashion. The periodic law states the properties of elements are periodic functions of their atomic numbers. The Russian chemist Dmitri Mendeleev is generally credited with organizing the first periodic table. To demonstrate the utility of Mendeleev’s periodic table, three elements, namely, gallium, scandium, and germanium, had not been observed and hence were unknown when the table was first published in 1872. Using information contained in his periodic table along with holes in the table, Mendeleev was able to accurately infer the existence and chemical properties of these three missing elements. Even today, chemists and physicists rely on the immense predictive power of the periodic law. The modern periodic table looks very different from Mendeleev’s, but it is organized according to the periodic repetition of chemical and physical properties. Figure 2.3 illustrates a modern version of the periodic table. Each box contains the chemical symbol of an element, along with its atomic number and its average atomic mass. The elements are listed in order of increasing atomic number, so each successive element has one additional proton. The vertical columns are called groups or families. Elements in a given group have similar chemical and physical properties. Unfortunately, there is more than one numbering system for the groups. The simplest system numbers the groups from 1 to 18. While this is the simplest and the officially accepted system, the authors strongly feel the older system of numbering groups by a number from one to eight, along with a letter (A or B), is a much more useful system. For example, the elements listed in the column on the far right of the table (Group 8A or Group 18, depending on which version of the periodic table you are working with) are called the noble gases. They are all colorless, odorless gases, and they all are extremely reluctant to combine with other elements to form compounds. images Figure 2.3 Periodic Table of the Elements Each row on the periodic table is called a period. The first period contains hydrogen and helium. The second period begins with lithium and ends with neon. Because each successive element has one additional proton, each successive element also has one additional electron. In fact, most chemists tend to focus on the electrons, rather than the protons, as a means of predicting chemical and physical proclivities of the elements. Periods represent adding electrons to quantum energy levels in the atom, which are called electron shells. Atoms at the end of a period each have an electron shell filled to its capacity with electrons. Although a detailed treatment of electronic configuration of atoms is beyond the scope of this text, and is not necessary to understand the remaining material, it is instructive to consider how the number of electrons in an atom relates to electron shells. As shown in Figure 2.4, a hydrogen atom has a single electron in the first electron shell, and a helium atom has two electrons, enough to fill the first energy shell. The light blue circle with the atomic symbol represents the atomic nucleus, and the darker blue path represents the region in space where you’re likely to find an electron in the first quantum state of the atom (i.e., the first shell). images Figure 2.4 The First Electron Energy Shell Lithium, in addition to the two electrons that fill its first electron shell, has one electron in the second electron shell, as illustrated in Figure 2.5. The region encompassed by the second shell is shown by a larger dark blue circle. Similarly, beryllium has two electrons in the second shell, boron has three, and so forth. Neon, a noble gas located at the end of the second period, has enough electrons to fill the second electron shell. Atoms (or ions) with filled electron shells are especially stable, and there is a strong energetic tendency for atoms to react in a way so as to acquire as many electrons as a noble gas. Therefore, elements that have the highest electron shell nearly filled to capacity tend to accept additional electrons, forming negatively charged anions. Elements with nearly vacant electron shells tend to surrender the electrons from partially filled shells, forming positively charged cations. images Figure 2.5 The Second Electron Energy Shell Fluorine is element 9 and is located in Group 7A. How many electrons are in the second electron shell of a fluorine atom? How many electrons does a fluorine atom need in order to have as many as the nearest noble gas? What charge do you expect on a fluoride anion? Fluorine is in Group 7A; therefore, fluorine has seven valence electrons. Since addition of one electron would give fluorine as many electrons as the nearest noble gas (Ne), fluorine forms an ion with a charge of negative 1. Average Atomic Weights The atomic weights listed in the periodic table are weighted averages of the atomic masses of the naturally occurring isotopes of that element. For example, consider the element chlorine. The atomic number is 17, and an average atomic mass of 35.45 is listed on the periodic table. Yet no chlorine atom has a mass of 35.45 amu, because that would require a fractional part of a neutron. The solution to this conundrum comes from considering that about 76% of all naturally occurring chlorine atoms have a mass of ~35 amu, while 24% of all naturally occurring chlorine atoms have a mass of ~37 amu. The value reported on the periodic table is a weighted average of these two exact masses. To calculate the average atomic mass, we begin with the precise values of the atomic masses and percent abundance of each isotope. We see that 75.77% of Cl has a mass of 34.97 amu and 24.23% of Cl has a mass of 36.97 amu. You probably learned to calculate an average by adding up all the values and dividing by the number of data points. A mathematically equivalent calculation of an average is to multiply each value times the percent of the population that value represents. Of course, the sum of the percent occurrences must total 100%. images The average is equal to the total of these products. This method is more convenient when the sample is very large and cannot be easily counted. Applying this strategy to chlorine, we obtain: images Classifying Elements on the Periodic Table Classifying elements as representative, transition, or inner transition elements is one of the most useful distinctions on the periodic table. The representative elements are contained in the “high-rise” portions located at the left and right extremes of the periodic table. In Figure 2.6, the representative elements are contained in the gray boxes. In the older numbering system, representative elements have a group number with an A. Transition elements, shown in blue boxes, have a B designation in their group number and form the connection between the representative high-rise towers. The inner transition elements (shown in green) are the “footnotes” located at the bottom of the periodic table. Most of the elements on the periodic table are metals and are listed on the left side of the table. Metals have a characteristically shiny luster. They tend to be ductile (able to be drawn into wires) and malleable (able to be beaten into thin sheets). Metals are good conductors of both heat and electricity. They tend to react chemically to form cations by giving away electrons from partially filled electron shells. Figure 2.7 lists the metallic elements in gray boxes. Nonmetals are located on the right side of the periodic table and are in dark blue boxes. Nonmetals may be solids, liquids, or gases. The solid nonmetals tend to be brittle. With the exception of carbon in the form of graphite, they do not conduct electricity. If they form ions, nonmetals tend to form anions. Metalloids (or semimetals) have properties intermediate between the metals and nonmetals and are listed in light blue boxes in Figure 2.7. Metalloids have a shiny luster, but they are less malleable and ductile than metals. They conduct electricity but not nearly as well as metals. For this reason, semimetals are called semiconductors. Silicon is the most well-known of the semimetals because of its use in constructing semiconductor computer chips. Most of the elements are solids under normal conditions. Only two (mercury and bromine) are liquids, although gallium has a melting point of around 30°C and will liquefy in your hand. Hydrogen, nitrogen, oxygen, fluorine, chlorine, and all of the noble gases are the gases under normal conditions. Figure 2.8 illustrates this information. Solids are listed in gray boxes, gases in blue boxes, and liquids in red boxes. images Figure 2.6 Representative and Transition Elements images Figure 2.7 Metals, Nonmetals, and Metalloids images Figure 2.8 Solid, Liquid, and Gaseous Elements images SOME COMMON ELEMENTS Every element has a chemical symbol. In many cases, the chemical symbol is the first two letters of the element’s name. While 118 elements have been reported in the chemical literature, you are likely to encounter only 30 to 40 of these in your nursing studies. The following paragraphs outline a few chemical and physical properties of some common elements as well as some medical applications for the most common elements. This information is not presented for you to memorize. Rather, it is presented for you to gain an appreciation of the myriad of important roles these elements play in your careers in the medical field. Aluminum (Al) Aluminum is a silvery white metal with a relatively low density of 2.7 g/cm3. For this reason, aluminum is a popular material for construction. Alloying aluminum with other metals improves its strength. Elemental aluminum does not occur in nature, and must be synthesized by the energy-intensive Hall process. Compounds containing aluminum are found in antiperspirants (aluminum chloride) and antacids (aluminum hydroxide). Barium (Ba) Barium sulfate (BaSO4) is given orally or as an enema to patients who are undergoing radiographic procedures involving the digestive tract. Because barium is a heavy metal, it is relatively opaque to x-rays and thus improves the definition of the gastrointestinal (GI) tract. Although all compounds containing barium are toxic, the solubility of barium sulfate is very low (2.5 mg/L of pure water), and patients excrete the material before they absorb a fatal dose. Bromine (Br) Elemental bromine exists as a diatomic molecule Br2 and is a reddish-orange, fuming, highly toxic liquid. Calcium (Ca) Calcium is a silvery white metal. It does not occur in nature in its elemental form. However, compounds containing calcium are the inorganic components of bone. Carbon (C) Carbon occurs in nature as two common varieties: graphite and diamond. You are probably familiar with diamonds, and you encounter graphite as pencil lead and charcoal. Highly purified and anhydrous graphite is known as activated charcoal, which can be administered orally to adsorb certain poisonous materials that a patient might have ingested. Different forms of the same element are called allotropes. Carbon is arguably the most versatile of all chemical elements, at least in terms of its ability to combine with other elements to form a staggering number of different compounds. In fact, an entire branch of chemistry (organic chemistry) is devoted to studying the compounds of carbon. Chlorine (Cl) Chlorine, like bromine, is a diatomic molecule, Cl2. Chlorine is a toxic green gas that has excellent disinfectant properties. Chlorine gas dissolves in sodium hydroxide to give sodium hypochlorite (NaOCl), which you probably know as Clorox®. Chromium (Cr) Chromium is a silvery white metal. It forms many highly colored compounds, hence the name chromium (Greek, khromo, and color). Chromium is an essential component of the iron alloy known as stainless steel. Cobalt (Co) Cobalt is a silvery white metal. Cobalt chloride absorbed onto a piece of felt can measure the relative humidity in air. When the air is humid, cobalt chloride picks up water from the air to form a reddish-purple hydrate. When the air is dry, cobalt chloride releases the water of hydration and turns blue. Copper (Cu) Copper is a reddish metal. All metals are variations of silvery white except for copper and gold. Copper is an excellent electrical conductor. The most important application of copper in a clinical setting is as wires in electronic instruments. Fluorine (F) Fluorine is a yellowish, poisonous gas. In its natural state it is a diatomic molecule, F2. Sodium fluoride is added to drinking water to strengthen teeth. Other fluoridation sources include sodium monofluorophosphate and stannous fluoride. The polymer of tetrafluoroethylene is a strong, slippery solid known as Teflon®. Gold (Au) The chemical symbol for gold is Au, after aurum (Latin for sun). Gold is often used for electrical contacts because of its excellent electrical conductivity, combined with its virtual imperviousness to corrosion. Helium (He) Helium is a colorless inert gas named after the sun (Greek, helios), because that is where it was first discovered. Liquid helium is used as a coolant in MRI instruments. Hydrogen (H) Hydrogen is the most common atom in the universe, and accounts for more than 95% of all known ordinary matter. On Earth, hydrogen is a colorless, flammable gas that is found as a diatomic molecule, H2. The name “hydrogen” literally means “water forming” and hydrogen reacts violently with oxygen to give water. Hydrogen represents a tantalizing energy alternative to fossil fuels, but current methods of producing hydrogen consume significant quantities of fossil fuel. Iodine (I) Iodine is a purplish-black solid. Like its vertical neighbors in the periodic table, bromine and chlorine, iodine is a diatomic molecule, I2. The topical antiseptics, tincture of iodine and betadine, both contain iodine. Iron (Fe) Iron is arguably the most important construction metal. In addition to buildings and cars, iron alloyed with chromium, molybdenum, nickel, and carbon form surgical stainless steel. Each hemoglobin molecule, the protein that transports oxygen in the blood, contains four ferrous (Fe+2) ions, each of which serves as a point of attachment for an oxygen molecule. Lead (Pb) The chemical symbol for lead comes from the Latin plumbum, which also gives us the word “plumber.” It is highly malleable and ductile and has been known since antiquity. One ancient, albeit poorly chosen, application of lead was to fashion water pipes, and hence the connection to the word “plumber.” Lithium (Li) Lithium is a silvery, highly reactive metal. Lithium is used in batteries and compounds containing lithium are used to treat bipolar disorder. Magnesium (Mg) Magnesium is a silvery white metal. Magnesium sulfate (Epsom salts) is used to slow down uterine contractions in preterm labor. Mercury (Hg) Mercury is a silvery white liquid metal. Because of its high density, mercury is used in sphygmomanometers. It is also found in some thermometers. Before its toxic nature was fully understood, mercury compounds had been used in medical applications ranging from treatment of syphilis to constipation. Mercury alloys well with many other metals and alloys containing mercury are known as amalgams. Neon (Ne) Neon is a colorless inert gas that is used in some lighting applications. Nickel (Ni) Nickel is a silvery white metal that plays more of a supporting role in medicine. For example, alloys containing nickel are components in such diverse applications as stainless steel and magnets. Nitrogen (N) Nitrogen is an odorless and colorless gas that occurs as a diatomic molecule, N2. Nitrogen gas comprises about 80% of air. Nitrous oxide (N2O) is an important anesthetic gas. Oxygen (O) Oxygen is an odorless and colorless reactive gas. Diatomic oxygen (O2) comprises roughly 20% of air. Oxygen is a very strong oxidizing agent. That is, oxygen has a strong tendency to accept electrons from other chemical species. This chemical property finds application in the electron transport chain [the biochemical pathway that is coupled to adenosine triphosphate (ATP) synthesis]. Triatomic oxygen (O3) is called ozone, which is a highly toxic gas with a characteristic sharp odor. Ozone is produced by electrical discharges. In the upper atmosphere, ozone absorbs ultraviolet radiation and provides us some protection from skin cancers. Phosphorus (P) Red phosphorus is used to make matches. The white allotrope of phosphorus is a much more dangerous material. White phosphorus causes horrific burns. In biological systems, phosphorus is found in genetic materials (RNA and DNA) and in high-energy molecules such as ATP. Potassium (K) Potassium is a silvery white metal. Because of its high reactivity, elemental potassium is not found in nature. Potassium chloride is a component in “Lite Salt.” Potassium and sodium ions are required for muscle contractions. Silicon (Si) Silicon is a lustrous silvery gray material. Because silicon conducts electricity, but not as well as a metal, silicon is classified as a semimetal. Crystals of pure silicon that have been doped with arsenic or gallium are known as semiconductors and are used to fabricate computer chips. Silicone rubbers are polymers containing silicon, oxygen, and various hydrocarbon groups, and are used in applications ranging from sealants to breast implants. Silver (Ag) The chemical symbol for silver comes from the Greek argentum, for white or shining. Silver is the best of all electrical conductors. Alloys of silver and mercury were once used in dental fillings, although the toxicity of each of these metals has detracted from this application. Silver also finds application in photography (including x-rays). When exposed to light, compounds such as silver chloride are more easily reduced to metallic silver. X-rays that are not blocked by the patient activate the silver emulsion. Developing the image reduces the activated silver chloride to finely divided silver metal, which appears as the black portions of the x-ray image. The unexposed silver compounds are washed away in the fixing process, leaving the white areas of the x-ray image. Sodium (Na) The chemical symbol for sodium comes from the Latin natrium, which means swimmer. When a small piece of sodium is placed in water, it skitters around the surface, like a swimmer in a pool. It reacts with water to give sodium hydroxide and hydrogen gas. The hydrogen sometimes ignites. Larger samples of sodium simply explode. Sodium ions, along with potassium ions, are required for muscle contractions. Sulfur (S) Sulfur is a yellow solid. Iron–sulfur clusters are found in cytochrome enzymes. The sulfur-containing amino acid cysteine is common in hair. Cysteine residues can connect to each other via disulfide bridges, giving hair a natural curl. Permanent waves are achieved by artificially removing and then reforming these disulfide bridges. Tin (Sn) Tin is a silvery white metal. Solder is an alloy of tin and lead and is used in electrical connections. Stannous fluoride (SnF2) was once a common ingredient in toothpaste, but has largely been replaced by sodium monofluorophosphate. Titanium (Ti) Titanium is a grayish metal often used in the manufacture of prosthetic implants because of its light weight, low toxicity, and high strength. Titanium oxide is used in white pigments, especially in paints. Zinc (Zn) Zinc is a bluish silver metal. Medical applications of zinc compounds include calamine lotion and zinc oxide (sun block). Galvanized steel is resistant to corrosion and is prepared by coating iron with a thin layer of zinc. images CHEMICAL NOMENCLATURE The rules for naming chemical compounds depend on whether the substance is a molecular substance or an ionic substance. Molecular compounds are comprised only of nonmetals. Ionic compounds are almost always comprised of a metal and a nonmetal. If a compound contains one of the polyatomic ions listed in Table 2.1, it is an ionic compound. Table 2.1 SOME COMMON POLYATOMIC IONS CHARGE NAME AND FORMULA +1 NH4+ ammonium ion H3O+ hydronium ion −1 HCO3− bicarbonate ion or hydrogencarbonate ion NO2− nitrite ion NO3− nitrate ion HSO3− bisulfite or hydrogensulfite ion HSO4− bisulfate or hydrogensulfate ion OH− hydroxide ion C2H3O2− acetate ion ClO− hypochlorite ion CN− cyanide ion H2PO4− dihydrogenphosphate ion −2 CO32− carbonate ion HPO42− hydrogenphosphate ion SO32− sulfite ion SO42− sulfate ion −3 PO43− phosphate ion Notice that chemical names are not proper nouns and should not be automatically capitalized. FORMULA NAME N2O Dinitrogen monoxide (commonly: nitrous oxide) NO Nitrogen monoxide (commonly: nitric oxide) SCl2 Sulfur dichloride P2O5 Diphosphorus pentoxide CCl4 Carbon tetrachloride SiO2 Silicon dioxide Several molecular compounds have common (nonsystematic) names (see the following table), and must be memorized. Sorry. FORMULA NAME COMMON USES H2O Water Drinking; chemical solvent NH3 Ammonia Fertilizer; window cleaner CH4 Methane (natural gas) Heating C3H8 Propane LPG fuel gas used in rural areas N2O Nitrous oxide Laughing gas; anesthetic Naming Molecular Compounds Molecular compounds are easier to name than ionic compounds, so let’s begin there. The molecular formula of a substance gives the number of each kind of atom in the molecule. To name a molecular substance: imagesName each element imagesIndicate how many of each element is present with a prefix multiplier (mono = 1, di = 2, tri = 3, tetra = 4, penta = 5, hexa = 6, hepta = 7, and octa = 8) imagesAdd the suffix “ide” to the last element name Naming Ions and Ionic Compounds An ion is an atom or group of atoms with a charge. Cations are positively charged and anions are negatively charged. Ionic compounds consist of ions and are held together by ionic bonds, or the attraction of the oppositely charged ions. In the solid state, ionic compounds form crystalline lattices in which all the cations are attracted to all the neighboring anions, and vice versa. Since you cannot identify any anion that is associated with any particular cation, there are no discrete ionic “molecules.” Ionic compounds are sometimes referred to as salts. You are no doubt familiar with common table salt, NaCl. While NaCl is certainly a salt, there are many other salts besides NaCl. Technically, a salt is produced by the reaction of an acid and a base, which is a subject for a later chapter. For now, you can consider all ionic compounds as being salts. Monatomic Cations of Representative Metals Representative metals almost always form cations in which the ionic charge equals the group number. This is because the group number is equal to the number of electrons in the highest energy, partially filled electron shell. By giving these electrons away, a representative metal is able to obtain an electron configuration that is identical with the closest noble gas. All of the metals in Group 1A form cations with a charge of +1. All of the metals in Group 2A form cations with a charge of +2. Aluminum forms a cation with a charge of +3. To name a representative cation, name the element and add “cation” or simply “ion.” There are no simple cations with charges of +4. For example, sodium is in Group 1A, and forms a cation with a charge of +1. Sodium metal has 11 electrons, and one of these electrons is in the third electron shell, all by itself. By giving away that electron, the resulting sodium cation has the exact number of electrons as neon, and all of its electrons are in filled shells. imagesPredict the charge on the ions that are formed from Ba, Rb, and Tl. Answer: Ba2+; Rb+; and Tl3+ Monatomic Anions of Representative Nonmetals For anions of representative elements, the ionic charge is based on the number of electrons the nonmetal needs to gain in order to have as many electrons as the nearest noble gas. For example, let’s look at oxygen on the periodic table. Oxygen is two boxes away from neon, the nearest noble gas. Therefore, when forming an anion, oxygen will acquire two electrons and gain a charge of −2. Nitrogen forms an anion with a charge of −3, while fluorine forms an anion with a charge of −1. Again, however, it is virtually impossible to form an anion with a charge greater than −3. To name monatomic anions, add the suffix “ide” to the stem name. Cl− chloride ion S2− sulfide ion P3− phosphide ion Transition-Metal Cations Most transition metals form more than one cation. For example, iron commonly forms two different cations: Fe2+ and Fe3+. It is not as easy to predict the charges on the cations that transition metals are likely to form, and most beginning students usually wind up memorizing the list. A few examples of some common transition metal cations are given in the following. Ag +1 only Ag+ silver cation Zn +2 only Zn2+ zinc cation Cu +1 and +2 Cu+ copper(I) cation or cuprous cation Cu2+ copper(II) cation or cupric cation Fe +2 and +3 Fe2+ iron(II) cation or ferrous cation Fe3+ iron(III) cation or ferric cation If the transition metal forms only one cation, you name it like a representative metal cation: Name the element and call it a cation. If the transition metal forms more than one cation, you need to name the metal and then indicate the charge on the cation with Roman numerals in parentheses. Fe3+ is the iron(III) cation Sn2+ is the tin(II) cation An older system for naming transition metals is to name the lower charged ion as the “ous” ion and the higher charged ion as the “ic” ion. This system is becoming less common in general academic use, but is still frequently encountered in medical and industrial settings. Cr2+ is the chromous ion Cr3+ is the chromic ion If the chemical symbol is based on the Latin or Greek name of the element (i.e., the chemical symbol isn’t the first two letters of the element’s name), you need to use the Latin or Greek stem name. Fe2+ is the ferrous ion Fe3+ is the ferric ion Polyatomic Ions Polyatomic ions are formed from two or more nonmetal atoms that are bonded together in a way that results in a net electrical charge. The subtleties of predicting the charge and formula of these ions is fairly involved, and you should content yourself with learning the ions listed in Table 2.1. Some of these ions merit special comment. Some ions, like SO42− and SO32−, differ only in a single oxygen atom. In these cases, the ion with the larger number of oxygen atoms is given the “ate” suffix, while the ion with the smaller number of oxygen atoms is given the “ite” suffix. SO32− is the sulfite ion SO42− is the sulfate ion Some of the ions, for example, HCO3−, contain a hydrogen atom. They are formed by combining the parent ion (CO32− in this case) with an acid (H+ ion). CO32− + H+ → HCO3− These “half acid salts” can be named in two ways. The systematic way is to simply name both components: HCO3− is formed from a hydrogen ion plus a carbonate ion, and is, therefore, named hydrogencarbonate. The common, if less systematic, approach is to call this the bicarbonate ion. Formulas of Ionic Compounds As we mentioned earlier, compounds (like atoms) must be electrically neutral. The net charge on an ionic compound must be zero. When a metal “gives” its electrons away to form a cation, there has to be some other species, often a nonmetal, present to accept the electrons. Thus, whenever a cation is forming, there is also a concurrent formation of an anion. Chemical systems have to remain electrically neutral. As you recall, molecules are comprised of atoms chemically bonded into a discrete and identifiable unit. There are no ionic molecules, because every cation is attracted to every anion, so there are no identifiable ion pairs that belong exclusively to each other. Therefore, the formula of an ionic compound is an empirical formula. That is, the formula of an ionic compound lists the simplest ratio of cations to anions necessary to achieve electrical neutrality. For example, calcium oxide contains Ca2+ ions and O2− ions. While the formulas CaO and Ca2O2 both represent electrically neutral combination of ions, the subscripts in the latter formula have a common factor of 2. Therefore, Ca2O2 is not the simplest ratio of calcium cations to oxide anions, and so the formulation of calcium oxide as Ca2O2 is incorrect. The correct empirical formula of calcium oxide is CaO. When forming an ionic compound, the total positive charge contributed by the cation(s) must be equal and opposite to the total negative charge contributed by the anion(s). For ion pairs with equal (but opposite) charges, this ratio is obviously 1:1. IONS FORMULA OF IONIC COMPOUND Na+ and Cl− NaCl Ca2+ and O2− CaO What about when the ionic charges aren’t equal to each other? The most mathematically sophisticated way to determine this ratio is to seek the least common multiple between the absolute values of the charges on the cation and anion. Most beginning students, however, simply use the “criss-cross” method, as shown in Figure 2.9. That is, the number of cations in the formula is the absolute value of the charge on the anion. The number of anions in the formula is the absolute value of the charge on the cation. For example, the formula of the ionic compound containing aluminum ions and oxide ions is Al2O3. images Figure 2.9 Formula of an Ionic Compound Here are some more examples: IONS FORMULA OF IONIC COMPOUND Na+ and CO32− Na2CO3 Mg2+ and PO43− Mg3(PO4)2 NH4+ and SO42− (NH4)2SO4 Ionic Compounds To name an ionic compound, you just name the cation and then the anion. There is a crucial difference between naming ionic compounds and molecular compounds. In molecular compounds you must include prefix multipliers (di, tri, etc.) to indicate the number of each kind of atom in the molecule. In ionic compounds you must not include prefix multipliers, because the number of each ion in the formula unit is controlled by the charges on the ions. If the cation is a representative element, it is not necessary to indicate the charge, because (with few exceptions) these metals form cations with an ionic charge equal to the group number. FORMULA NAME K2SO4 Potassium sulfate Na2O Sodium oxide Li2CO3 Lithium carbonate FeSO4 Iron(II) sulfate or ferrous sulfate Fe2(SO4)3 Iron(III) sulfate or ferric sulfate When naming ionic compounds that contain transition-metal cations, you need to indicate the charge on the cation, either by including Roman numerals to indicate the charge or by using the “ic/ous” suffixes. But how do you determine the charge on the cation from the formula? You have to learn the charges on the anions and assign a charge to the cation so that the formula achieves electrical neutrality. For example, let’s consider the last two examples. FeSO4 contains an iron cation and sulfate anion. Since the sulfate anion has a charge of −2, the iron must have a charge of +2. Therefore, FeSO4 is iron(II) sulfate. Fe2(SO4)3 contains three sulfate anions. Since each sulfate carries a −2 charge, there are a total of six negative charges contributed by the sulfate anions. Therefore, there must be six positive charges distributed between the two iron cations. Thus, the charge on the iron cations must be +3, and Fe2(SO4)3 is iron(III) sulfate. FeSO4 Iron(II) sulfate or ferrous sulfate Fe2(SO4)3 Iron(III) sulfate or ferric sulfate Hydrates Some ionic compounds incorporate a fixed number of water molecules into their formula unit. The compound that contains the water is called a hydrate, and removal of the water affords the anhydrous salt. Compounds that have a strong tendency to absorb water are called hygroscopic. To name a hydrate, you simply name the ions and then add the appendage hydrate, along with a multiplier to indicate the number of water molecules in the formula. CuSO4·5H2O Copper(II) sulfate pentahydrate MgSO4·7H2O Magnesium sulfate heptahydrate Naming hydrates only makes sense when you are dealing with solid substances, because when a hydrate is dissolved in water, both the ions and the waters of hydration separate and mix uniformly with the water solvent. The anhydrous form of a compound that has a strong tendency to absorb water can be used as a desiccant. Desiccants scavenge the last traces of water from a system. One of the most commonly used desiccants is silica gel (SiO2). Addition of water to a desiccant is a reversible process, so hydrated forms of a desiccant can be used as moisturizers. Formulas From Names To assign a chemical formula of a compound from its name, you first must recognize whether the compound is ionic or molecular. For ionic compounds, you must also know the charges on the ions. images ELECTROLYTES. Video 2.1 We most commonly encounter electricity as a flow of electrons through copper wiring in our homes and offices. However, electricity is more generally described as the flow of charged particles under the influence of an electric field. We can’t have an electric current in a system unless there are charged particles that are free to move around. That brings us to an important concept in both physiology and chemistry: electrolytes. An electrolyte is a substance that dissolves in water to give a solution that conducts electricity. A nonelectrolyte is a substance that dissolves in water to give a solution that does not conduct electricity. While most ionic compounds are only sparingly soluble in water, those few ionic compounds that readily dissolve in water are electrolytes. Molecular compounds are nonelectrolytes, unless they have acid or base properties. We explore acids and bases in a later chapter. For now, let’s just consider molecular compounds to be nonelectrolytes. COMPOUND IONIC OR MOLECULAR? FORMULA Calcium sulfide Ionic CaS Chromium(III) acetate Ionic Cr(C2H3O2)3 Cupric hydroxide Ionic Cu(OH)2 Nitrogen triiodide Molecular NI3 Sulfur trioxide Molecular SO3 It is a remarkable thing for an ionic compound to dissolve in water. You probably learned at some point that opposite charges attract each other. The energy cost of separating positively charged cations from negatively charged anions is immense. Dissolution occurs only because water interacts very effectively with ions. We explore this phenomenon more fully in Chapter 8. For now, however, you just need to accept that when ionic compounds dissolve in water, they (mostly) separate into ions that freely and independently move around in the solution. Since these ions are free to move around in the solution, the solution conducts electricity. Most beginning chemistry students believe water conducts electricity, because of the (very reasonable) prohibition against using a hair dryer in the bathtub. The fact is, water is a nonelectrolyte. Now, let’s be clear: There is a very good probability that you will electrocute yourself if you use an electrical device in the bathtub, but that is because water in the bathtub comes from the tap which contains a fair concentration of several electrolytes, such as NaCl. Water is a molecular substance, because it is a compound of nonmetals. Pure water is a nonelectrolyte and is a very poor conductor of electricity. images STOICHIOMETRY Stoichiometry includes the calculations that relate amounts of reactants and/or products in a chemical reaction. You, no doubt, covered this topic in depth during your undergraduate chemistry course. For our purposes here, we need only the basics. Moles Moles are a quantity of material, analogous to a dozen. In the case of moles, however, the number is much larger. A mole is an amount of substance that contains exactly as many particles as there are in exactly 12 g of carbon-12. This number is often called Avogadro’s number, and it is equal to 6.02 × 1023 particles/mol. “Particles” could mean molecules, atoms, ions, or electrons. Notice Avogadro’s number has two units: particles and moles. Therefore, Avogadro’s number is a conversion factor between particles and moles. Molar Mass (Molecular Weight) Chemists use moles mainly because molecules are just too small to deal with on an individual basis. So, we gather 6.02 × 1023 of them together into a mole, and we use that as our working unit in chemistry. So what is the mass of 1 mole of carbon? Well, the system is set up so that the molar mass (expressed in g/mol) of an element is equal to its atomic mass (expressed in amu). For molecules, the molar mass is equal to the sum of the masses of the component atoms. Most chemists use the terms molar mass and molecular weight interchangeably, even though mass and weight are not the same concept. So, for example, the molar mass of magnesium sulfate (MgSO4) is: 1 Mg × (24.3 g/mol) + 1 S × (32.1 g/mol) + 4 O × (16.0 g/mol) = 120.4 g/mol Since molar masses have units of grams and moles, they are conversion factors between grams and moles. SUMMARY imagesChemistry studies matter and the changes it undergoes. imagesChanges can be physical or chemical. A chemical change produces a new substance. A physical change transforms a substance into a different state, but it’s still the same substance. imagesChemical properties describe the chemical changes that a sample undergoes (e.g., flammability). imagesPhysical properties can be observed without changing the chemical nature of the sample (e.g., mass, volume, color, and density). imagesMatter is anything that occupies space and has mass. imagesAtoms are the basic building blocks of all matter. imagesAtoms are comprised of protons (mass ≈ 1 amu; charge = +1), neutrons (mass ≈ 1 amu; charge = 0), and electrons (mass ≈ 0 amu; charge = –1). imagesThe number of protons is the atomic number of an atom and determines the identity of the atom. imagesThe number of protons plus the number of neutrons is the mass number of the atom. imagesIsotopes contain the same number of protons, but a different number of neutrons (i.e., same atomic number but different mass number). imagesIn a neutral atom, the number of electrons equals the number of protons. imagesIf there are more electrons than protons, the net charge on the atom is negative, and it is called an anion. imagesIf there are fewer electrons than protons, the net charge on the atom is positive, and it is called a cation. imagesA pure substance cannot be separated into its components through physical changes. imagesA pure substance that consists of only one kind of atom is called an element. There are about 118 known elements. A pure substance that is comprised of more than one kind of atom is called a compound. There are millions of different compounds reported in the chemical literature. imagesMolecules consist of two or more atoms chemically bonded into a discrete unit called a molecule. Molecules that consist of only one kind of atom (e.g., O2) are elements. However, most molecules are compounds (e.g., CO2). imagesIonic compounds consist of anions and cations. Ionic compounds are not molecules because every anion is attracted to every cation, so none of the ions are bound into a discrete unit. imagesJohn Dalton is credited with the atomic theory that postulates all matter is comprised of indestructible atoms. While this theory contains some inaccuracies in its details, it still forms the foundation upon which modern chemistry is based. imagesDmitri Mendeleev first organized the known elements into a periodic table demonstrating the chemical and physical properties of elements repeated in a predictable, periodic fashion. The modern periodic table organizes elements by increasing atomic number. Rows of elements are called periods and represent electron energy shells filling. Columns are called groups or families. Elements in a given family have similar chemical and physical properties. imagesThe atomic weights on the periodic table represent average atomic weights, based on the relative abundance of the naturally occurring isotopes of an element. imagesRepresentative elements are located in the “high-rise” ends of the periodic table. The transition elements occupy the center of the periodic table. The inner transition elements are the “footnotes” at the bottom of the periodic table. imagesNonmetals are located on the right-hand side of the periodic table. Nonmetals may be solids, liquids, or gases. Nonmetals tend to form anions and to be nonconductors of electricity and heat. imagesMetals are located on the left side through the center of the periodic table. Metals are almost always solids and tend to form cations. Metals are malleable, ductile, and good conductors of both heat and electricity. imagesMolecular compounds are comprised of two or more nonmetals. To name a molecular compound, name each element and add the suffix “ide.” If there is more than one atom of a particular element, include a prefix multiplier (di = 2, tri = 3, etc.). imagesCations are named as the metal. If the metal can form more than one charge on a cation, the charge of the cation is included as a Roman numeral in parentheses. Representative metals form cations with charges equal to the group number. imagesSimple monoatomic anions are named by adding the suffix “ide” to the stem name of the nonmetal (e.g., chloride). Representative nonmetals form anions with charges equal to the group number minus 8. imagesPolyatomic ions have more than one atom in the ionic unit. The names of common polyatomic ions are given in Table 2.1. imagesIonic compounds are named by first naming the cation and then naming the anion. Prefix multipliers are not needed because the ratio of cations to anions is dictated by the charge on each ion. imagesElectrolytes are compounds that dissolve in water to give a solution that conducts electricity. Ionic compounds that dissolve in water are strong electrolytes. Molecular compounds that dissolve in water are normally nonelectrolytes. REVIEW QUESTIONS FOR CHEMISTRY BASICS 1.List and define the five major areas of chemistry. 2.Classify and describe types of matter. 3.What is the difference between physical and chemical changes? 4.Give one physical property of water and one chemical property of water. 5.What is the difference between intensive and extensive physical properties? 6.Give one intensive physical property of water and one extensive physical property of water. 7.Density is calculated from two extensive physical properties, namely, mass and volume. Is density an intensive or an extensive physical property? 8.Define and describe molecules, atoms, compounds, and mixtures. 9.What are isotopes? 10.Can a molecule be an element? Explain. 11.Give the mass number, atomic number (Z), proton number (P), neutron number (N), and electron number (E) for the following: 1H, 4He, 6Li, and 8Be. 12.What is the difference between mass number and average atomic mass? 13.Naturally occurring bromine consists of two isotopes, 79Br and 81Br, in roughly equal amounts. What is the average atomic mass of bromine? 14.Describe how a mass spectrometer works. 15.Describe the organization of the periodic table (periods, groups, and group number). 16.What is the difference between metals, nonmetals, and metalloids? 17.What is an ion? What is a cation? What is an anion? How do ions form? 18.Is there a trend in the periodic table about which kind of ion an element is likely to form? 19.How do you predict the charge of the ions derived from the representative elements? 20.What’s a hydrate? 21.How do you decide whether a compound is molecular or ionic? 22.What charge ion is sodium likely to form? How about a phosphide ion? How about a barium ion? 23.What are the representative elements? The transition elements? 24.“Lactated Ringer’s” contains sodium lactate. If the formula of sodium lactate is NaC3H5O3, what is the charge on the lactate ion? (Lactate = C3H5O3 with some unspecified charge.) 25.Is glucose an ionic or molecular compound? The molecular formula of glucose is C6H12O6. 26.What is the molar mass of nitrous oxide? 27.If a patient is given images of nitrous oxide, how many molecules of nitrous oxide have been given? HINT: Use the molar mass to convert grams into moles, and then use Avogadro’s number to convert moles into molecules. 28.What is the difference between a period and a group on the periodic table? 29.Provide a name or chemical formula for each of the following compounds or ions, as required. a. Sodium bicarbonate i. CuCO3 q. Dinitrogen monoxide b. Potassium chloride j. PO43− r. Lithium dihydrogen phosphate c. Ammonia k. Fe3+ s. Nitrogen dioxide d. MgSO4 l. Na2HPO4 t. AlCl3 e. Carbon tetrachloride m. NH4+ u. Calcium carbonate f. NH4NO3 n. Carbon monoxide v. Sodium fluoride g. Ferrous sulfate O. PCl3 w. Ozone h. Mg3(PO4)2 p. KCl x. BaSO4 30.Which of these is a chemical property of nitrous oxide gas, rather than a physical property? a.Nitrous oxide is less dense than oxygen gas. b.Nitrous oxide is flammable. c.Nitrous oxide is colorless. d.All of these are physical properties. e.All of these are chemical properties. 31.You give a glass of (pure) water and a hamburger to a severely dehydrated patient, who then immediately throws up. The vomit is an example of a ___, while the water is an example of ___. a.Homogeneous mixture; element b.Homogeneous mixture; compound c.Heterogeneous mixture; element d.Heterogeneous mixture; compound 32.Based on ions that the elements we discussed in class typically form, which of these is an UNLIKELY compound? a.Al3O2 b.BeO c.NaF d.FeS 33.Which of these is a common property of metals? a.Ductility b.Good electrical conductivity c.Tendency to form cations d.Shiny and lustrous surface e.All of the above 34.Which of these statements is true of the elements symbolized by images and images? a.X and Y are isotopes of each other. b.X and Y are in the same chemical family. c.Y has more neutrons but fewer protons than X. d.X and Y have the same atomic number. e.None of these statements is correct. 35.Which of these lists only representative metals? a.Na, B, C, N, O b.C, Si, Ga, Sn c.Li, Na, K, Rb d.Fe, Co, Ni, Cu e.Ce, Pr, Ne, Pm 36.What cation is each of these metals likely to form? a.Al b.Rb c.Mg d.Li e.Ga 37.What anion is each of these nonmetals likely to form? a.S b.I c.N d.P e.Se 38.Based on the trends discussed in this chapter, give the formula and name of the ionic compound formed between these pairs of elements. a.Mg and N b.Al and S c.Li and I d.K and O e.Ca and C 39.Give the name of each of these ions. a. CO32− d. OH− g. PO43− b. SO42− e. NH4+ h. HSO3− c. NO2− f. Fe3+ i. H2PO4− 40.Give the formula of each of these ions. a. Ferrous ion d. Sulfate g. Sulfite b. Hydroxide e. Bicarbonate h. Hydrogen sulfate c. Phosphate f. Carbonate i. Dihydrogen phosphate 41.Give the formula of each of these ionic compounds. a. Sodium bicarbonate f. Copper(II) acetate b. Potassium phosphate g. Iron(II) sulfate c. Lithium carbonate h. Nickel(II) oxide d. Ammonium chloride i. Ammonium nitrate e. Barium oxide j. Silver(I) chloride 42.Give the formula of each of these molecular compounds. a. Carbon disulfide f. Oxygen difluoride b. Iodine trichloride g. Nitrogen dioxide c. Nitrogen triiodide h. Nitric oxide d. Diphosphorus pentoxide i. Nitrous oxide e. Ammonia j. Sulfur tetrachloride 43.Sodium dodecyl sulfate (SDS) is the surfactant in Tide®. If the formula of this ionic compound contains one sodium ion and one dodecyl sulfate ion, what is the charge on the dodecyl sulfate anion? 44.Soap scum is largely comprised of magnesium stearate. If magnesium stearate has a formula Mg(C18H36O2)2, what is the charge on the stearate anion? What is the formula of iron(III) stearate? 45.Give the name of the element that fits these criteria. a.The lightest element b.A noble gas in the third period c.The halogen that is a liquid at room temperature and pressure d.The alkali metal that is in the second period e.The semimetal in the fourth period that has the larger atomic number f.The element whose allotropes include diamond and graphite g.The fourth period element whose properties are most similar to nitrogen 46.The permanganate ion has the formula MnO4−. What is the formula of the pertechnetate ion? 47.If the chromate ion has the formula CrO42−, what is the formula of the tungstate ion? 48.Aqueous solutions of which of these substances do you expect to be a strong electrolyte? a.NaCl b.Ethanol, C2H6O c.Glycerin, C3H8O3 d.Lithium pyruvate, LiC3H3O3 e.Ammonium carbonate 49.Lidocaine (C14H22N2O) is not very soluble in water. Mixing lidocaine with hydrogen chloride gives lidocaine hydrochloride, which is very soluble in water. A solution of lidocaine hydrochloride is a good conductor of electricity. Which of these statements is true? If the statement is false, explain why it is false. a.The solubility of lidocaine is a physical property. b.Conversion of lidocaine into lidocaine hydrochloride is a physical change. c.Lidocaine is a strong electrolyte. d.Lidocaine hydrochloride is an ionic compound. 50.Which of the tenets of Dalton’s atomic theory are still considered correct today? If there is a problem with one of the tenets, cite an example that contradicts that tenet. (Note: All of these counterexamples are founded on technologies that were not available to Dalton.) a.Atoms of a given element are all identical. b.Atoms are neither created nor destroyed in a chemical reaction. c.Matter is comprised of tiny particles called atoms. d.Atoms are indivisible. e.Compounds are formed by combining atoms in a fixed ratio by mass. images 1 The Sun, for instance, is a very massive body that is composed mostly of plasma. Plasma is a distinct phase of matter in which the nuclei of atoms and electrons move about at extremely high speeds. 2 Charge = 1 g C (1 mol/12 g)(1 mol e-/mol C)(1 Faraday/mole e-)(96,500 C/Faraday) = 8,000 C. 3 Actually, it depends on the mass-to-charge ratio of the ion. However, it is unusual for the ionization sector to remove more than one electron. Therefore, the charge on the molecular ion is almost certain to be +1. Therefore, the mass/charge ratio is equal to mass/1, which is numerically equal to the mass of the particle.