a preliminary draft of chaptercontemporarychemistry.com/.../ch1_introchemswfbk.pdf · and...

A Preliminary Draft of Chapter 1 of an eBook

“Contemporary Chemistry”

Conrad TrumboreBecky KinneyKyle Kinney

WARNING

In order to interact with this eBook, you will need to installAdobe Reader 9 on your computer. If you have problems,

you should uninstall earlier versions of Adobe Reader.

Click HERE to install Acrobat Reader 9

Once you have installed this reader, the figure belowshould be activated and be running a looped animation.

Contact us

http://www.adobe.com/products/reader/mailto:[email protected]:[email protected]

Chapter 1 A Brief Overview of Chemical Principles Page 1-1

CHAPTER 1

A BRIEF OVERVIEW OF CHEMICAL PRINCIPLES

This chapter introduces some of the most basic chemical principles and provides abeginning chemical vocabulary. Succeeding chapters introduce other chemical conceptsand vocabulary on a need-to-know basis in the context of our contemporary world.

Questions answered in this chapter1. What is chemistry and how does it relate to other sciences?

2. What are the basic building blocks of matter?

3. What is the difference between mass and weight?

4. What is the periodic table of elements?

5. What is a chemical reaction? A nuclear reaction?

6. What is an isotope? Why are some isotopes radioactive?

7. What is the difference between concentration and density?

The nature of scienceScience depends on systematic observations ofnature. From these observations, scientists putforward hypotheses, educated guesses that aretestable by experiment. An experiment is anobservation carried out in a controlled mannerso that the results can beduplicated. There is noscience without this abilityto duplicate otherscientist’s observations! Ifa scientist’s observationsare comprehended in termsof analogies with otherobjects or concepts, this iscalled a model. The scientist does moreexperiments to test this model. If the

Typical sequence of events leading to an established scientific theory:

• Observation• Hypothesis• Experiment• Tentative theory• Experiment to test theory• Refined theory• Publication and criticism• Possible revision of theory after more experiments• Publication of revised

theory with little or no criticism

• Acceptance by a vast majority of scientists


hypothesis and the model fit all of the data from all experiments, and if the scientistcan explain these data in terms of other more primitive scientific phenomena, thisexplanation is called a scientific theory. A model helps to organize a body of data. Atheory can be used to predict the results of future experiments. A scientific law is aconcise statement or mathematical equation about a basic relationship in nature.

The Big Bang hypothesis (Chapter 2) regarding the sudden expansion of theuniverse around fourteen billion years ago has now been corroborated by so manyexperimental observations that it is now an accepted model. Some scientists havereservations about certain parts of the model. It is not a theory because it cannotexplain what happened earlier than a fraction of a second during the Big Bang, and itcannot predict with certainty the future fate of the universe. However, it is currentlythe most popular model available to explain where we are in the evolution of theobservable universe. On the other hand, the law of gravity allows everyone to predictexactly the attractive gravitational forces between all objects from tennis balls toplanets. There are no scientists who publicly dispute this law. There have been noexceptions to this law! If there were, it would cease to be a scientific law.

Exercise 1-1 Models, theories, and lawsCan you name some other scientific models, theories, and laws? Justify theirdesignations according to the above definitions.

Chemistry, natural sciences, and medicineTraditionally chemistry has been divided into five fields:organic (the chemistry of carbon chains or rings with orwithout oxygen and nitrogen and other elements-seebelow for definitions of carbon, oxygen, and nitrogen),inorganic (deals with substances that don’t containcarbon as their principal element),analytical (deals with techniques thatyield information about chemical

systems), physical (primarily theoretical chemistry), andbiochemistry (chemistry of biological systems). The barriersseparating these fields are falling rapidly. Chemists like todesignate chemistry as the “central” science (see figure to the right)because all sciences deal in one way or another with chemicals andchemical concepts. There is a great deal of overlap betweenchemistry biology, physics, and geology. There has been a gradualmerging of chemistry and other fields such as molecular biologyand biochemistry, geochemistry (geology and chemistry),biogeochemistry (biology, geology, and chemistry) and chemicalphysics (chemistry and physics). Advances in chemistry havebeen crucial to nearly all advances in the medical sciences. Some ofthese advances have depended on new chemical techniques and others have dependedon new chemicals synthesized in the laboratory.

Scientificlaw andtheory

Fieldsof

chemistryFields of Chemistry

OrganicInorganicAnalyticalPhysicalBiochemical


What is chemistry? Matter? Mass? Weight?Chemistry is the study of the properties, composition, and structure of matter, andthe changes matter undergoes. Matter is anything that possesses mass when at restand is observable by the senses. Mass is a measure of a body’s resistance to being

accelerated. Therefore, a truck is more difficult to move than asmall car because there is more resistance to accelerating the largermass of the truck.

The closely related property of matter, weight, is thegravitational force with which the Earth, or any other mass attractsanother mass. The gravitational force exerted upon an object isdirectly proportional to the mass of the object. However, in outerspace, where there is only a small gravitational pull from the Earthbecause of the distance from the Earth, the weights of objects would

both be nearly zero, that is, they are “weightless” in space. However, their masses inouter space would be the same as they are on Earth. This is because in outer spaceobjects with different masses will still have different resistances to acceleration.

MASS/WT

Definitionof

chemistry

Massvs.

weight


The chemical building blocksOne of the building blocks of matter is the atom. An atom is the smallest componentof matter that still retains its chemical identity duringchemical reactions. The smallest and lightest kind ofatom, hydrogen, is postulated to have formed about100,000 years following the first moments of the BigBang expansion (Chapter 2).

Atoms can be broken down into theircomponent parts. For example, if we heat a hydrogenatom (Fig. 1-1) to temperatures comparable with thoseon the Sun, we obtain an exceedingly small, exceedinglylight, negatively charged (–) particle called an electronand an exceedingly small nucleus consisting of a single,positively charged (+) proton. All atoms have nucleiand all nuclei have at least one proton. The mass of aproton is several thousand times greater than the massof an electron.

All atoms consist of a single nucleus and one or more electrons. Atoms otherthan hydrogen have more than one proton in their nuclei. The number of protons

contained in the nucleus is calledthe atomic number, representedby the letter Z. The atomic numberof hydrogen is 1 because there isonly one proton in the hydrogenatom’s nucleus. Nuclei other the Hatom also contain neutrons, whichare electrically neutral particleswith approximately the same massas that of the proton. Neutrons arethought to be the earliest chemicalspecies present during the Big Bangevent. By neutral, we mean thatthe object is neither positively (+)nor negatively (–) charged. An

object may be neutral because it either has no electrical charge, such as a neutron, or ithas equal numbers of positive and negative charges and therefore has no net (excess)electrical charge. Atoms are neutral because the number of negatively charged electronsin the atom is exactly equal to the number of positively charged protons in theirnuclei.

Figure 1-1 Depiction of a hydrogenatom containing one positivelycharged nucleus (proton) and onenegatively charged electron which isattracted to the proton because of itsopposite charge.

Atomscontaina singlenucleus

andelectron(s)

Atomicnumber =# protonsin nucleus

Element Atomic Symbols Numbers Name of Element

(Z)

H 1 Hydrogen

He 2 Helium

C 6 Carbon

N 7 Nitrogen

O 8 Oxygen


PERIODIC TABLE PRACTICE

Any atom whose nucleus contains one proton (Z = 1) is chemically identifiedas hydrogen (H); any atom whose nucleus contains two protons (Z = 2) is helium(He); and one whose nucleus contains three protons (Z = 3) is lithium (Li), etc.The small section of the table shown in the above animation is only the first threerows of a much larger list of the elements. A listing of all the known elements iscontained in a table of elements known as the periodic table (Table 2-1), consistingof all the known elements arranged in rows (periods) with increasing atomic numbersand columns containing elements with similar chemical characteristics. The atomicnumber is listed below the element’s symbol.

Periodictable


Periodic Table

1A 2A 3B 4B 5B 6B 7B / 8 \ 1B 2B 3A 4A 5A 6A 7A 8A1 H

1He2

2 Li3

Be4

B5

C6

N7

O8

F9

Ne10

3 Na11

Mg12

A l13

S i14

P15

S16

Cl17

A r18

4 K19

Ca20

Sc21

Ti22

V23

C r24

Mn25

Fe26

Co27

Ni28

Cu29

Zn30

Ga31

Ge32

As33

Se34

B r35

K r36

5 Rb37

S r38

Y39

Zr40

Nb41

Mo42

Tc43

Ru44

Rh45

Pd46

Ag47

Cd48

In49

Sn50

Sb51

Te52

I53

Xe54

6 Cs55

Ba56

La57

Hf72

Ta73

W74

Re75

Os76

I r77

Pt78

Au79

Hg80

Tl81

Pb82

Bi83

Po84

At85

Rn86

7 F r87

Ra88

Ac89

Rf104

Db105

Sg106

Bh107

Hs108

Mt109

The symbol H is used to represent a neutral hydrogen atom, which iscomposed of an intimately bound negative electron and positively charged proton.Each substance containing only atoms with the same atomic number (Z) is designatedas an element. Elemental carbon is a substance that is composed of atoms thatcontain 6 protons in each of the atomic nuclei making up the elemental substance.There may be several different forms of an element called allotropes. For example,there are three forms of elemental carbon: diamond, graphite, and recently discoveredforms called “buckyballs” and “carbon nanotubes.” The differences in the externalproperties among these forms are explained by the different internal spatialarrangements of the carbon atoms.

Table 1-1 Periodic table of the chemical elements. Elements are arranged in horizontal rows orperiods with increasing atomic number (the number of positively charged protons in the nucleus shownbelow the symbol of the element) and vertical groups that have similar chemical properties. (The14lanthanide and 14 actinide elements following La and Ac, respectively, are not shown.)

Exercise 1-2 Atomic numbers and elements in the periodic table

Locate each of the following elements in the periodic table (Z = atomic number) :carbon (C), Z = 6; lithium (Li), Z = 3; fluorine (F), Z = 9; sodium (Na), Z = 11; sulfur(S), Z = 16; nitrogen (N), Z = 7; oxygen (O), Z = 8.

Element


Superscripts in the upper right hand corner of an element represent the net

charge of the chemical species, – for an excess unit of negative charge and

+ for an

excess unit of positive charge. The hydrogen atom, H, containing one proton and oneelectron, has no superscript because the single positive and the single negative chargescancel each other’s charge and the atom is electrically neutral. The symbols

representing the electron and proton are e– and H

+, indicating each has a net charge of

one, but also indicating that they are oppositely charged.

An ion is an atom or a group of atoms with a net positive or negative charge.Thus a hydrogen atom without its electron is a positive ion (H

+), a proton. A high

temperature plasma is composed, in part, of positively charged ions and negativelycharged electrons. Minutes after the Big Bang, according to the model, a very hightemperature plasma consisting of neutrons, positively charged nuclei, and negativelycharged electrons is postulated to have formed (Chapter 2).

Attraction and repulsion of charged particlesExperimental measurements in the laboratory demonstrate that:

(1) all negatively charged (–) particles repel negatively charged (–) particles;(2) all positively charged (+) particles repel positively charged (+) particles.(3) all positively charged (+) particles attract negatively charged (–) particles,

These observations lead to the general principle that, at room temperature, oppositelycharged particles attract each other and similarly charged particles repel each other.Thus, when free electrons encountered free electrons, and free protons encounteredfree protons in the Big Bang plasma, there should have been, at least initially, a strongrepulsion.

Buckyball (above), at the atomic level,with carbon atoms at the intersectionsof the lines in the general shape of aminiature soccer ball; discovered insoot. There are 80 C (carbon) atoms inone form of this element.

Diamond Graphite

Hydrogenatom

Ionsand

Plasma

Chargedparticle

interactions


CHARGED PARTICLE INTERACTION

However, it also has been experimentally established that when temperaturesare exceedingly high, as they must have been in the Big Bang plasma, and particlespeeds are very high, positively charged particles in a plasma can undergo forcefulenough collisions to overcome like-charge repulsion at very short distances betweennuclei. When nuclei get this close, different nuclear forces take over so that attractivenuclear forces are dominant and nuclear reactions are now possible. Because of this,new nuclei and therefore new atoms can form during such high-energy nuclearcollisions.


Symbols used in nuclear reactionsIn order to accurately represent nuclear reactions, it is convenient to provide thefollowing information regarding particles in the proposed Big Bang plasma:

(1) The chemical identity of the atoms; thisis represented by one large capital letterrepresenting the symbol of the element(e.g., “H” stands for hydrogen) or twoletters, one upper case, one lower case(e.g., “He” represents helium. This symbolhad to be given two letters; there are more

than 26 elements and H was already taken).

(2) The net charge, representing the algebraic sum of the charges of theprotons and electrons in the chemical species; this is placed in theupper right hand corner; He2+ represents a helium ion with noelectrons because the algebraic sum of the nuclear charge (2+) and thecharge from electrons (0) equals 2+ [(2+) + (0) = 2+].

(3) The atomic number (Z), the number of protons in the nucleus isplaced in the lower left hand corner; this is redundant information,because if you know the identity of the element, you also can find itsatomic number Z from the periodic table.

(4) The mass number (M), the total number of protons and neutrons inthe nucleus, is placed in the upper left hand corner.

As an example of this naming system, we examine three different kinds ofhydrogen ions, each containing a single proton, and, for the heavier ions, one and twoneutrons, respectively. These different nuclei are called isotopes, defined as one oftwo or more nuclei or atoms having the same atomic number but different massnumbers.

The proton is a hydrogenatom nucleus with both anatomic number and a massnumber of one and therefore hasa single positive charge. Theproton is one of three isotopesof hydrogen. According to therules outlined above, theappropriate symbol for the

proton is represented as: 11H +

Symbols for

elementsMass Number (M) Net charge(#protons+#neutrons)

Symbol of Element

Atomic number (Z)(#protons in nucleus-determines element!)

Atomicnumber

MassNumber

Isotopes


MATCHING ATOMIC NO, ETC.

A deuteron is a nucleus containing one proton combined with one neutron.The atomic number of the deuteron is the same as that of the proton (Z = 1) becausethe deuterium nucleus is still chemically identified as hydrogen. However, thedeuteron has a mass number equal to 2 (M = 1 proton mass + 1 neutron mass = 2).Again, the deuteron nucleus contains no electrons and therefore has a positive charge.

A deuteron is therefore represented as12H +. The deuterium atom, containing one

electron and one deuteron nucleus, would be neutral ( 12H ), i.e., no + charge in the

upper right hand corner of the symbol, because the single negative electron neutralizesthe single positive charge of the deuteron nucleus to yield a neutral atom.

The tritium atom contains a radioactive nucleus. Nuclei are radioactive whenthe composition of these nuclei makes them unstable, causing them to transform(decay) into new, more stable nuclei, usually giving off particles such as electrons oreven nuclear fragments such as helium nuclei from more massive nuclei. The timeperiod during which radioactive nuclei undergo radioactive decay ranges from fractionsof a second to many millions of years, depending on the type of radioactive nuclei.For example, tritium has a half-life of 12 years. This means that half of a large

Protonvs.

deuteron

Radioactivenuclei


population of H-3 nuclei will undergo radioactive decay during an interval of 12 years,and half of the remaining population will decay away in another 12 years, and soforth. During each half-life period, the population of similar radioactive nuclei isreduced by one half.

When discussing hydrogen isotopes, the symbolism H-1, H-2, and H-3 isoften used to describe hydrogen isotopes containing one proton in combination with0, 1(deuterium - D), and 2(tritium - T) neutrons, respectively. Physical properties ofchemical species containing different hydrogen isotopes differ. For example, heavywater (D2O) containing all deuterium atoms has different properties from light water(H2O). D2O has a density (see below for a definition of density) that is larger thanH2O and thus has been given the name heavy water. Heavy water is used in sometypes of nuclear reactors because of its heavy hydrogen isotope.

A neutron, represented in nuclear equations by the symbol 01n , has a mass

number = 1, contains no protons, and is electrically neutral.

Atomic mass is the mass of a particular atom relative to the standard atomicmass of the carbon-12 isotope of exactly 12. Note that no atomic mass is an absolute

mass, but instead allows comparison among various atoms of their relative masses.Atomic mass is inappropriately sometimes called “atomic weight.” One atomic massunit (amu) is one-twelfth the mass of a carbon-12 atom. Using this referencestandard mass, the H-1 isotope is 1.00728 amu and the oxygen isotope O-16 is16.000 amu. Elements found in nature consist of a mixture of isotopes. For example,hydrogen contained in water consists mostly of H-1 with small amounts of theheavier isotopes H-2 and H-3. Thus, the atomic masses of natural substances includethese mixtures of naturally occurring isotopes. Periodic tables lists the average of theatomic masses of all the naturally–occurring isotopes of an element. The average

Example 1-3 Atomic numbers and mass numbers

What are the mass number, the atomic number, and the number of neutrons in the

tritium nucleus (31 H+)?

The mass number is 3 for tritium. The atomic number is 1, because there is onlyone proton. To obtain the number of neutrons, we subtract the number of protons(1) from the mass number (3) and find that there are two (2) neutrons. To checkour answer, we add the number of protons (1) and neutrons (2) and the sum (3)should be equal to the mass number listed on the upper left hand corner of theisotope.

Exercise 1-4 Atomic numbers and mass numbers

What are the mass number, atomic number, and number of neutrons in He-3?(Remember He stands for a helium.). Locate helium in the periodic table.

Atomicmass

Atomicmass unit


atomic mass of hydrogen is listed as 1.00794 amu because of the relatively smallamounts of hydrogen isotopes heavier than H-1 present in nature.

Nuclear and chemical reactionsChemical reactions and nuclear reactions are events in which a substance is orsubstances are transformed into one or more new substances over a period of timethat can range from fractions of a second to years.

Chemical ReactionsIn a chemical reaction, all atoms retain their identities during the reaction,

but are transformed into new arrangements of the same atoms in space forming newsubstances called products. The substances that react with each other to formproducts are called reactants. An example of a chemical reaction between twohypothetical molecules, designated A and B, is shown on the next page. During acollision between A and B, a chemical reaction takes place and the atoms in A and Bare rearranged into two new molecules (C and D) if the collision is sufficientlyenergetic.

In a nuclear reaction, one or more elements can be transformed into newelements through a collision of nuclei with each other or by the transformation of oneradioactive element into another by the emission of a particle from its nucleus. In bothof these types of reactions, energy can be absorbed or released. Many nuclearreactions of interest give off large quantities of energy compared with chemicalreactions, for example in nuclear reactors or nuclear weapons.

Both chemical and nuclear reactions can be represented as equations. In amathematical equation, e.g., (3 + 2) = 5, the equals sign represents an identity. In achemical or nuclear equation, the equals sign is replaced by an arrow generallypointing from left to right. To the left of the arrow are the chemicals present beforethe reaction, the reactants, and to the right of the arrow are the chemicals resultingfrom the chemical or nuclear reaction, the products.

Chemicalreaction

Products&

reactants

Nuclearreaction

Equation

AC

B D


Thus, in a hypothetical chemical or nuclear reaction in which reactants A and B reactto form the products C and D, the reaction is written as reaction (1-1):

A + B → C + D (1-1)

All atoms involved in chemical reactions retain their identity. That is, in a chemicalequation a hydrogen atom may be a part of the chemical A and remains a hydrogenatom when it winds up in the chemical D.

ABCD ANIM.

Note that these hypothetical reactants A and B and contain atoms that are rearrangedduring the formation of products C and D. Note also that there is an intermediatestage, a state of transition between reactants and products, called a transition state,during which neither reactants nor products are present. It is during this period thatreactant chemical bonds are broken and new product chemical bonds are formed.

Nuclear ReactionsFor nuclear reactions, we generally need to write equations with more isotopicinformation than with chemical reactions because elements may change their chemicalidentity during the reaction. In the example below, we utilize isotopic symbols torepresent a specific nuclear reaction, one of the simplest nuclear reactions that isthought to have occurred immediately following the Big Bang.

Nuclearreactions


----------------------------------------------------------------------------------------------------An Example of a Nuclear Reaction in the Big Bang Plasma

It is suggested in Chapter 2 that an important nuclear reaction in the Big Bangplasma was the interaction of a neutron and a proton as reactants to form a deuteronand a gamma ray as products. A gamma ray (γ) is an energetic radiation with zeromass and zero charge originating in many nuclear reactions and is given off during theradioactive decay of many unstable nuclei. One can think of a gamma ray as a highlyenergetic x-ray. Gamma rays carry away large quantities of excess energy and areabsorbed in surrounding matter, resulting in the generation of heat and chemicaldamage to that matter. The above word description of this nuclear reaction isrepresented in diagram form in Fig. 1-2:

The same nuclear reaction depicted in Fig. 1-2 is represented below in equation formin (1-2):

11H + + 01n → 12H

+ + gamma ray (γ) (1-2)

In all nuclear reactions, the sum of the mass numbers of the reactants must equal thesum of the mass numbers of the products (the numbers found in the upper left handsuperscripts of reactants and products). This same relationship applies to the sumsof atomic numbers of reactants and products (found in the lower left subscripts ofreactants and products). Furthermore, the algebraic sum of the electrical charges of thereactants must equal the (algebraic) sum of the electrical charges of the products.Check to see that all of these relationships are valid in equation (1-2). The gamma rayhas no mass or charge.------------------------------------------------------------------------------------------------------

Gamma(γ) ray

Typicalnuclearreaction

Figure 1-2 Representation of a nuclear reaction in which a neutron and aproton collide forming a deuteron and a gamma ray.


NUCLEAR ANIM.

Chemical equations and ionizationA chemical equation is a symbolic expression that represents in an abbreviated formthe laboratory observations of a chemical change. There are a number of general typesof chemical equations. We first introduce the type of chemical equation representingionization, which is needed to understand processes occurring during and after theproposed Big Bang.

Ionization of an atom is the removal of one or more negatively chargedelectrons from the neutral atom to form a positive ion. When the hydrogen atomabsorbs a very large amount of energy, like that available through collisions in the BigBang plasma, it ionizes and dissociates, i.e., it comes apart into its component parts.In order to be ionized, the neutral hydrogen atom must absorb enough energy todissociate it into a free electron and a proton. This ionization of the hydrogen atomcan be represented in diagram form (Fig. 1-3):

Chemicalequation

Ionization


The process in Fig. 1-3 also can be represented by the following chemical equation:H + energy → H* (excess energy) → H + + e – (1-3)

IONIZATION ANIMS.

Rates of Chemical ReactionsChemical reactions take place in both time and space. The speed with which reactantsare converted into products is called the rate of the reaction. This rate is defined asthe number of products produced in a given volume of space in a given time. The rateis usually dependent on the number of collisions between reactants. The number ofcollisions is dependent on the reactant concentration, defined as the number ofmolecules or atoms that are present in a given volume of space. The number ofcollisions also depends on the temperature of the reactants, with more frequent

Figure 1-3 Ionization of ahydrogen atom to form a proton(a positive ion) and an electron(a negative ion)

Rate ofchemicalreaction

concentration


collisions and therefore more chemical reaction taking place at higher temperatures.There is a difference between a net chemical reaction and the sequence of reactions,called a mechanism, that actually lead to that net overall reaction.

For example, H2 and D2 are, respectively, the formulas for hydrogen anddeuterium molecules. At high temperatures, the overall chemical reaction betweenthese two molecules can be represented as:

H2 + D2 → HD + HD or, alternatively, H2 + D2 → 2HD (1-4)These equations could imply that the mere collision of H2 and D2 molecules causes achemical reaction forming HD molecules. Research has shown that, instead, at hightemperature, the following are some of the complex chemical reactions taking place: First, there are many energetic collisions between energy-rich molecules such as: H2 + H2 → H2 (very energy rich) + H2 (energy poor) (1-5) H2 (very energy rich) → 2 H atoms (molecule decomposes) (1-6) H atom + D2 → HD molecule (product) + D atom (reacts further) (1-7) D atom + H2 → HD (product) + H atom (1-8)The H atom from (1-8) can then react in reaction (1-7) to produce more HD product,etc. This sets up a chain reaction consisting of (1-7) and (1-8). If we add up all ofthese complex reactions, the net result is reaction (1-4). Some of these steps in thishighly complex mechanism are illustrated in the following animations.

REACTION KINETICS ANIMS.

Chemicalmechanism


Volume and densityVolume is the measure of the bounded space occupied by an object. Volume can becalculated from the dimensions of an object and can be measured in units such asquarts, gallons, or liters. One liter (1 L) is approximately the same volume as onequart. One milliliter (1 mL) is one thousandth of a liter and is equal to the volume of acube one centimeter on an edge (1 cm3 ), where 2.54 cm = 1 inch .

Density (d) is the amount of mass (m) contained in a certain volume (v) and can bedefined as density = d = mass/volume = m/v (mass divided by volume). Densities ofsolids and liquids are generally given in terms of grams per cubic centimeter (g/cm3).The density of water at 3.98°C is exactly 1.0000 g/cm3. “°C ” stands for degrees onthe Celsius temperature scale, where water freezes at 0°C and boils at 100°C.

Volume

2 liter soda bottle 1 quart ~ 1 liter milk carton ~ 1000 mL

1 cm3 = 1 mL

Density


DENSITY ANIMS.

Exercise 1-5 Density of water at room temperature

If the density of water is 0.998 g/cm3 at 20°C, how much volume will one gram of wateroccupy? (Hint: if d = m/v, then d v = m and therefore v = m/d. Remember to put unitswith each number you write and make sure units cancel properly in any calculation youperform.)

Example 1-6 Determination of Density

There are 314.4 grams contained in a 40.0 cubic centimeter block of pure iron. What isthe density of iron?

d = m/v = 314.4 grams/ 40.0 cm3 = 7.86 g/cm3

The above equation reads: density is equal to the mass per unit volume; for example,when 314.4 grams of a substance are contained in 40.0 cm3, this means there are 7.86 gof that substance in every cubic centimeter of that substance. This density is obtained bydividing 314.4 grams by 40.0 cm3. Note that the units grams and cm3 belong to thenumbers 314.4 and 40.0. They are both experimental quantities, not pure numbers.


Summary

1. What is chemistry and how does it relate to other sciences?

Chemistry is the study of the properties, composition, and structure of matter,and the changes matter undergoes. Chemists claim that chemistry is the “centralscience” because it interfaces with all other sciences and provides explanationsof phenomena in each of these sciences at the atomic or molecular levels.

2. What are the basic building blocks of matter?

Exceedingly small atoms (composed of nuclei and electrons) or substancesderived from atoms are the building blocks of all matter. Nuclei are much smallerthan atoms and are composed of positively charged protons and electricallyneutral neutrons. Electrons contain much less mass than nuclei and carry anegative electrical charge.

3. What is the periodic table of elements?

The chemical identity of an element is defined by the total number of protons inthe nucleus of an atom of that element. The atomic number (Z) of that element isequal to the number of protons in the nucleus of the element. The periodic tableis a table of all the elements arranged by increasing atomic number in a series ofrows with increasing atomic number. The chemical characteristics of theelements in the vertical columns of the periodic table are often similar.

4. What is the difference between mass and weight?

Mass is a measure of a body’s resistance to being accelerated. Weight is relatedto the gravitational force with which the Earth or any other mass attractsanother mass.

5. What is a chemical reaction? A nuclear reaction?

A chemical reaction is the result of a chemical transformation of reactant(s) intoproduct(s). In a chemical reaction, the chemical identity of all atoms is retained,but the geometrical relationship of atoms with respect to each other in threedimensional space is altered. A nuclear reaction is one in which nuclei react toform new nuclei, often forming a new chemical element or elements. Energy isoften released in chemical reactions, but the amounts released are generally muchlarger in nuclear than in chemical reactions.

6. What is an isotope? Why are some isotopes radioactive?

An isotope is one of two or more nuclei (or atoms) having the same atomicnumber (number of protons in its nucleus) but different mass numbers (the sum


of the number of protons and neutrons in a nucleus). Some isotopes areradioactive, that is, energetically unstable. These radioactive nuclei emit energeticparticles, such as negative electrons called beta rays. The emission of suchradiations often stabilizes the nucleus left as the product of the radioactivedecay.

7. What is density?

Density is the amount of mass contained in a unit volume and can be found bydividing the total mass of an object by its volume.

Exercises

Review Questions

1. List five “theories” you have heard or read about. Which of these can be characterized as scientific theories? Justify your reasoning in each case.

2. Define each of the following words and terms: chemistry, science, matter,mass, mass number, weight, proton, electron, neutron, atom, atomic number,equation, reactant, product, radioactive, gamma ray, deuteron, ion, ionization,periodic table, positive charge, neutral, negative charge, isotope, rate, nuclearreaction, and chemical reaction.

3. If a hydrogen atom is separated into its component parts, what are the parts? Arethese parts also atoms?

Problems

4. How many protons are there in the nuclei of each of the three isotopes of hydrogen?

5. Which contains more mass: (a) an H atom or H+; (b) H or D; (c) He-4 or Li-5;(d) He2+ or H+; (e) C-12 or C-14.

6. What is the nuclear composition of the deuterium nucleus? of the tritiumnucleus? Are these two species isotopes?

7. How many neutrons and protons are there in each of the following isotopes:H-2, He-3, He-4, Be-8, O-16, C-12? What are the mass numbers and atomicnumbers of each of these isotopes?

8. Fill in the missing isotopes in the following nuclear reactions:


(a) 21 H+ +11 H+ → _________ + γ

(b) 126 C 6+ + ______ →168

O 8+

(c) 11 H+ + ______ → 11 H

9. In both (a) and (b) in the question above, there are positive charges in the upperright hand corner of reactants and products. Why are these not neutral species?

10. How many mL are there in 1 L? How many cm3 are there in 1 dm3? (10 cm = 1dm; 1 dm = 0.1 meter)

11. An object that is made from pure lead weighs 42.8 g. Its volume is measured as3.77 cm3. What is the density of lead? (Include units in your answer.)

Readings

American Chemical Society 2006. Chemistry in Context: Applying Chemistry toSociety, McGraw Hill.

Hill, J. W. and Kolb, D. K. 2008. Chemistry for Changing Times, Prentice-Hall.

CoverPageCh1A(Principles)B copyCHAPTER 1 - A BRIEF OVERVIEW OF CHEMICAL PRINCIPLESQuestions answered in this chapterThe nature of scienceChemistry, natural sciences, and medicineWhat is chemistry? Matter? Mass? Weight?Mass vs. weightThe chemical building blocksNucleus building exercisePeriodic tableAttraction and repulsion of charged particlesAttraction and repulsion of charged particlesSymbols used in nuclear reactionsAtomic and mass numbersNuclear and chemical reactionsChemical reactionsReaction animatedNuclear reactionsNuclear reaction and energyChemical equations and ionizationIonization of H and He atoms

Rates of chemical reactions4 animations of the reaction of H2 and D2Volume and densityGas and solid densitySummaryExercisesFurther reading

Button1: Button2:

a preliminary draft of chaptercontemporarychemistry.com/.../ch1_introchemswfbk.pdf · and...

Documents