CHAPTER 4: CHEMICAL FOUNDATIONS:ELEMENTS, ATOMS, AND IONS

INTRODUCTION

In Chapter 4 you are introduced to the names and symbols of the common elements and ions.Make sure you learn the names and symbols now. Most of the chemistry covered in subsequentchapters depends upon a knowledge of these names and symbols. .If you are having difficultyremembering the names, use Table 4.3 in your textbook to make up some flash cards with theelement name on the front side, and the symbol on the back. Find several minutes each day todrill yourself with the cards until you have committed the symbols and names to memory.

The remainder of the chapter covers the categories of elements which are organized into th~

periodic table, and the formation of ions from atoms.

GOALS FOR THIS CHAPTER

AKnow how the isotopes of an element differ, and how to write and interpret X symbols

Zfor isotopes. (Section 4.7)Know how to determine the mass number, number of protons, number of electrons ornumber of neutrons for any isotope. (Section 4.7)Know what the symbols and numbers on a periodic table mean, what the major families ofelements are, and where to find them on the periodic table. (Section 4.8)Know how some elements exist when uncombined with other elements, and someproperties of common elements. (Section 4.9)

Know which elements are common on earth, and their relative abundances. (Section 4.1)Learn the names and symbols for the common elements given in Table 4.3 of your text.(Section 4.2)Learn Dalton's atomic theory and the law of constant composition. (Section 4.3)Know what a compound is, and how to write and interpret chemical formulas.(Section 4.4)Know the names and locations within the atom of the major subatomic particles.(Section 4.5)Understand how Rutherford's gold foil experiment was performed and what information itprovided about subatomic structure. (Section 4.5)Know the sizes, relative masses and relative charges of the major subatomic particles.(Section 4.6)Understand why elements composed of the same subatomic particles can have differentproperties. (Section 4.6)

12.

11.

10.

5.

8.

3.4.

1.2.

7.

6.

9.

56

13. Know how atoms form anions, and how they form cations. Be able to predict what type ofion is formed, and its charge based on the location of elements within the periodic table.(Section 4.10)

14. Realize that compounds can be composed of ions and that in a molecule, the number ofnegative charges on the anions must equal the positive charges on cations. (Section 4.11)

15. Be able to write the chemical formula for compounds made from ions. (Section 4.11)

QUICK DEFINITIONS

Element symbols

Law of constantcomposition

Dalton's atomic theory

Atoms

Compound

Chemical formula

Subatomic particles

Electron

a-particle

One or two letter abbreviations based on modern or ancientelement names. (Section 4.2)

States that a compound always contains the same proportionsby mass of different atoms. This means that the composition ofa compound is always the same. (Section 4.3)

All elements are made of atoms. For anyone element, all the­atoms are the same. Different elements are made fromdifferent kinds of atoms. Atoms from different elements cancombine to make compounds. Each compound always has thesame relative numbers and kinds of atoms. Chemical reactionsdo not cause atoms to break apart into subatomic particles orcause new elements to form. (Section 4.3)

The smallest particles of which elements are composed.(Section 4.3)

A pure substance that always contains the same relativenumbers and kinds of atoms. (Section 4.4)

A representation of a compound that shows the symbol foreach element and how many atoms of each element are presentby using subscript numbers. (Section 4.4)

The individual units of which atoms are made. (Section 4.5)

A small subatomic particle with small mass and a negativecharge. Located outside the nucleus. (Section 4.5)

An alpha particle consists of two protons and two neutrons. Ithas a 2+ charge and is relatively heavy, compared with a singleproton or neutron. (Section 4.5)

Quick Definitions 57

Nuclear atom

Nucleus

Proton

Neutron

Isotopes

Atomic number

Mass number

Periodic table

Groups

Alkali metals

Alkaline earth metals

Halogens

Transition metals

58 4 Chemical Foundations

A model of the atom in which the positrve charge isconcentrated in one location, the nucleus, instead of beingspread over the entire atom. (Section 4.5)

The area where the positive charge of an atom is concentrated,and where the protons and neutrons are located. (Section 4.5)

A subatomic particle that has a positive charge equal in size tothe negative charge on an electron, but is much more massivethan an electron. Found inside the nucleus. (Section 4.5)

A subatomic particle that is only slightly more massive than aproton, and that has no charge. Found inside the atomicnucleus. (Section 4.5)

Different kinds of atoms of the same element. Each isotope ofan element has the same number of protons and electrons, but adifferent number of neutrons. (Section 4.7)

The number of protons in the nucleus of an atom. (Section 4.7)

The number of protons plus neutrons. (Section 4.7)

A way to organize the elements so that families of elementswith similar properties are found grouped together in columnsof the table. (Section 4.8)

Families of elements with similar properties. Certain columnsin the periodic table are referred to as groups. (Section 4.8)

Elements in the first column (group 1) of the periodic table.(Section 4.8)

Elements in the second column (group 2) of the periodic table.(Section 4.8)

Elements in group 7 of the periodic table. (Section 4.8)

Transition metals are the elements in the middle columns of theperiodic table, to the left of the heavy jagged line, and to theright of the alkaline earth metals. (Section 4.8)

Metals

Nonmetals

Metalloids

Noble gases

Diatomic molecules

Ion

Cation

Anion

Ionic compounds

PRETEST

All elements to the left of the heavy jagged line in the periodictable. Most metals appear shiny, can conduct electricity, canbe beaten into thin sheets, and can be drawn into fine wires.(Section 4.8)

Any of the elements to the right of the heavy jagged line of theperiodic table. The characteristics of the nonmetals vary fromelement to element. (Section 4.8)

Elements that border the heavy jagged line on the right side ofthe periodic table. They have some characteristics of metals,but not all. They are also called semi-metals. (Section 4.8)

Elements that are found in group 8 of the periodic table. Theydo not readily react with other elements to form compounds.(Sections4.8 and 4.9)

Molecules that are composed of two atoms of the sameelements. (Section 4.9)

An atom or group of atoms that has either lost one or moreelectrons (has a positive charge) or gained one or moreelectrons (has a negative charge). (Section 4.10)

An ion with a positive charge. It has lost one or moreelectrons. (Section 4.10)

An ion with a negative charge. It has gained one or moreelectrons. (Section 4.lO)

Compounds made by reacting a metal with a nonmetal. Thecompound contains cations of the metal which are attracted tothe anions of the nonmetal. (Section 4.11)

1. Which element is most abundant in the human body?

2. What are the symbols for the elements sodium, phosphorus, and silver?

3. What modifications to Dalton's Atomic Theory were made as new information aboutatoms was collected?

Pretest 59

4. What is the chemical formula for a compound that contains 2 atoms of hydrogen, 1 atom ofsulfur, and 4 atoms of oxygen?

5. The gold foil experiments of Ernest Rutherford demonstrate the existence of what part ofthe atom?

6. What is the relative mass of a neutron if the relative mass of an electron is zero?

7. How many protons, neutrons and electrons are in an isotope ofmolybedenum, Igg Mo?

8. Which elements are found in nature as diatomic molecules?

9. Write the equation for the formation of an anion from a neutral atom of bromine.

10. How many Ca2+ ions and cr ions are needed to form a compound? Write the formula for

the compound.

PRETEST ANSWERS

1.

2.

3.

4.

5.

6.

7.

8.

60

Oxygen is the most abundant element in the human body. (4.1)

The symbols for sodium, phosphorus and silver are Na, P, and Ag. (4.2)

Dalton's Atomic Theory was modified when isotopes were discovered. Originally, Daltonsaid that every atom of a particular element was identical. We now know that some atomshave different numbers of neutrons. (4.3)

A compound with 2 hydrogen atoms, I sulfur atom and 4 oxygen atoms would have theformula ~S04' (4.4)

When a few of the heavy alpha particles bounced back, Rutherford concluded that they hadcollided with a dense concentration of positive charge, the nucleus. (4.5)

If the relative mass of an electron is zero, the relative mass of a neutron is one. (4.6)

100An atom of 42 Mo would have 42 protons, 42 electrons and 58 neutrons. (4.7)

The elements hydrogen, oxygen, nitrogen, and the halogens fluorine, chlorine, bromineand iodine are found as diatomic molecules. (4.9)

4 Chemical Foundations

9. The equation' for the formation of an anion from a bromine atom is Br + e- ~ Br'.(4.10)

10. One Ca2+ will combiene with two cr ions to form the compound CaC12• (4.11)

CHAPTER REVIEW

4.1 THE ELEMENTS

How Many Elements Are There?

There are 109 elements at the present time, but that number will increase when scientistssynthesize new ones in the laboratory. Eighty-eight elements occur naturally. The remainder aremade in the laboratory.

Which Elements Are Most Abundant on Earth?

Oxygen (49.2 %), silicon (25.7 %), aluminum (7.50 %) and iron (4.71 %) are the four mostabundant elements on earth. The table below lists mass percents of many of the earth's elements.

Table 4.1 Common Elements Found on Earth

Distribution (Mass Percent) of the 18 Most Abundant Elementsin the Earth's Crust Oceans. and Atmosohere

Element Mass percent Element Mass Percent

Oxygen 49.2 Titanium 0.58Silicon 25.7 Chlorine 0.19Aluminum 7.50 Phosphorus 0.11Iron 4.71 Manganese 0.09Calcium 3.39 Carbon 0.08Sodium 2.63 Sulfur 0.06Potassium 2.40 Barium 0.04Magnesium 1.93 Nitrogen 0.03Hydrogen 0.87 Fluorine 0.03

All others 0.49

Chapter Review 61

Which Elements Are Most Abundant in the Human Body?

Oxygen (65.0 %). carbon (18.0 %), hydrogen (10.0 %), and nitrogen (3.0 %) are the mostabundant elements in the human body. There are many other elements present in smalleramounts, and some trace elements are present in very small, but detectable amounts. The tablebelow lists elements which are found in the human body.

Table 4.2 Common Elements in the Human Body

Abundance of Elements in the Human BodyTrace Elements

Major Elements Percent by Mass (in alphabetical order)

Oxygen 65.0 ArsenicCarbon 18.0 ChromiumHydrogen 10.0 CobaltNitrogen 3.0 FluorineCalcium 1.4 IodinePhosphorus 1.0 Manganese

Magnesium 0.50 Molybdenum

Potassium 0.34 NickelSulfur 0.26 SeleniumSodium 0.14 SiliconChlorine 0.14 VanadiumIron 0.004Zinc 0.003

4.2 SYMBOLS FOR THE ELEMENTS

You must learn the names and symbols for the common elements now, or you will have troubleunderstanding material later in the course. It is easier to learn the names and symbols if you firstbreak them up into smaller groups. Three categories of symbols are presented in the tables belowand in Table 4.3 in your textbook. Try learning the symbols and names one category at a time.

Symbols with one letter

BoronCarbonFluorineIodineNitrogenOxygen

62 4 Chemical Foundations

BCFINo

PhosphorusPotassiumSulfurTungstenUranium

PKSWU

Symbols with the first two letters of the element name

AluminumArgonBariumBismuthBromineCalciumCobalt

AlArBaBiBrCaCo

HeliumLithiumNeonNickelRadiumSiliconTitanium

HeLiNeNiRaSiTi

Symbols with two letters based on the original name

AntimonyArsenicCadmiumChlorineCopperGoldIronLeadMagnesium

SbAsCdCICuAuFePbMg

ManganeseMercuryPlatinumSilverSodiumStrontiumTinZinc

MnHgPtAgNaSrSnZn

4.3 DALTON'S ATOMIC THEORY

What Is Dalton's Atomic Theory?

All elements are made of atoms. For anyone element, all the atoms are the same. Differentelements are made of different kinds of atoms. Atoms from different elements can combine tomake compounds. Each compound always has the same number and kind of atoms. Chemicalreactions don't cause atoms to break apart into subatomic particles.

4.4 FORMULAS OF COMPOUNDS

How Can You Write and Interpret Chemical Formulas?

Compounds are substances composed of more than one kind of element. A particularcompound always contains the same relative numbers and kinds of elements. Chemicalformulas contain the one or two letter symbols for the elements to indicate what kinds of

Chapter Review 63

elements are present in the compound. Small numbers written below the level of the letters(subscript numbers) indicate how many atoms of each element the compound contains. Forexample, the compound dinitrogen tetroxide contains two nitrogen atoms and four oxygen atoms.You can write its formula by using the symbol for nitrogen followed by a subscript 2 and thesymbol for oxygen, followed by a subscript 4. Nz04• Don't use a subscript number when acompound contains only one atom of a particular kind. Nitrogen monoxide contains one atom ofnitrogen and one atom of oxygen. Its formula is written NO. We do not need subscripts fornitrogen and oxygen because the subscript 1 is understood. When you see the symbol for anatom which is not followed by a subscript, it means that the compound contains only one of thatparticular atom.

4.5 THE STRUCTURE OF THE ATOM

How Did J.J. Thomson Demonstrate the Existence ofSubatomic Particles?

For a long time scientists did not know what the atom was like. They did not have muchinformation to work with. In 1895, J.J. Thomson was able to make atoms emit particles with anegative charge. He could get all the elements he tried to emit these small particles, so heconcluded that atoms of all elements contain them. Thomson realized that overall, atoms are notpositively or negatively charged; they are electrically neutraL This meant that the small,negatively charged particles must be counterbalanced in the atom by something with a positivecharge. Thomson's experiments showed the existence of negatively charged particles(electrons), and showed that positively charged particles must exist as well.

What is the Plum Pudding Model of the Atom?

Scientists knew that there were negatively and positively charged particles in the atom, but until1911 did not have any firm evidence about how they were arranged. A model by Lord Kelvinstated that the electrons (negatively charged particles) could be evenly dispersed in a positivelycharged matrix, like raisins in a pudding. This is often called the plum pudding model of theatom.

How Did Rutherford Perform the Gold Foil Experiment?

In 1911 Ernest Rutherford performed some experiments that gave a much clearer understandingof what an atom is really like and how the subatomic particles are arranged. Rutherford used aheavy, positively charged particle called an a-particle to bombard a very thin (only several atomsthick) piece of gold foiL a-particles are tiny and cannot be seen with the naked eye, butRutherford could detect their presence by using a detector which produced a flash of light whenstruck by the a-particle. Each flash of light showed where an a-particle hit the detector andallowed Rutherford to follow the path of the a-particles.

64 4 Chemical Foundations

Gold foilSource of alpha

particles

)Shield

Narrow tubeproduces anarrow beamof a particles.

Zincsulfidescreendetector

Before the experiment, Rutherford predicted what he thought would happen when the a-particlehit the gold foil. He predicted that most of the a-particles would go right through the gold foiland hit the detector on the other side (Path A). Most of the a-particles did go right through thefoil. Rutherford also thought that some a-particles could come close to the part of an atomcontaining the positive charge and be repelled slightly, causing the positively charged a-particleto be somewhat deflected from its straight path (Path B). Rutherford was correct in thisprediction too. However, he did not predict that some of the a-particles would hit an area in thegold foil so dense and massive that the a-particle would bounce almost straight back, as though ithad hit a brick wall (Path C).

What Does Rutherford's Experiment Show?

Rutherford's experiment shows that atoms are mostly empty space, since most of the a-particlespassed through the gold foil without hitting anything. Some of the a-particles were deflectedslightly from their straight path. Those particles came close to but did not hit an area in the atomwhich contained a positive charge. The a-particles were deflected because two areas of positivecharge tend to repel each other.

A few a-particles bounced almost straight back. This was surprising because the a-particle ismore massive than an individual proton or neutron. How could a heavy particle hit a relativelylight proton and bounce back? It meant that the a-particle hit a small area within a gold atomwhich was very massive because it contained all the protons in one place. This evidence ledRutherford to postulate that the positive charge is not spread all over the atom, as the plumpudding model stated, but is concentrated in one area, the nucleus.

Chapter Review 65

4.6 INTRODUCTION TO THE MODERN CONCEPT OF ATOMIC STRUCTURE

One part of Dalton's model states that all atoms of a single kind of element are exactly the same.We now know that some atoms of each kind of element are different from the others. Thedifference is in the number of neutrons in the nucleus. Atoms of a single kind of element whichcontain different numbers of neutrons in the nucleus are called isotopes.

What Is the Size ofan Atom?

Recent information has provided us with data about the size of an atom and an individualnucleus. Atoms themselves are very small. The nucleus is on average 10-13 em in diameter, andthe electrons are 10-8 cm away from the nucleus. Every atom has lots of empty space, and infact, if the nucleus of an atom were the size of a grape, the electrons would be found a mile awayfrom it.

What Are the Charges and Masses ofSubatomic Particles?

The relative masses and charges of the subatomic particles are important. The electron has beenassigned a relative mass of one and a charge of 1-. The proton has a relative mass of 1836, muchmore than an electron. The relative charge on a proton is 1+, equal in magnitude to an electron,but opposite in sign. The neutron has a relative mass the same as a proton, but no charge.

How Do Different Atoms, All with the Same Subatomic Particles,Have Such Different Properties?

Each kind of atom has a different number of protons and electrons. The chemistry of an atom isdetermined by the number and arrangements of the electrons, so each kind of atom can havedifferent chemical properties. The way elements react with other elements is determined by thenumber and arrangements of the electrons.

4.7 ISOTOPES

What Are Isotopes?

Each different kind of element contains the same number of electrons as it does protons, becauseatoms are electrically neutral. All atoms of each element always have the same number ofelectrons and the same number of protons. The number of protons and electrons never changes.For example, all boron atoms have five electrons and five protons. Most atoms also haveneutrons in their nucleus. Unlike protons and electrons, the number of neutrons in differentatoms of the same kind of element can vary. Atoms of the same kind of element with differentnumbers of neutrons in the nucleus are called isotopes. One isotope of boron has five protonsand five electrons and five neutrons. Another isotope of boron has five protons and fiveelectrons and six neutrons. Only the number of neutrons is different between the two isotopes ofboron.

66 4 Chemical Foundations

How Can We Show Different Isotopes ofan Element?

Chemists use the symbols ~X to help show which isotope is under discussion. X is the one or

two letter symbol for the element. Z represents the number of protons in the nucleus, also called

the atomic number. A is the mass number, equal to the number of protons plus the number of

neutrons. For any element, Z will remain the same, regardless of which isotope we are

discussing. A, which is the number of protons plus neutrons, will vary. For example, 151 B

represents the isotope of boron (called boron-l l) which has a mass number of eleven and an

atomic number of five. 1~ B represents the isotope of boron with a mass number of ten and an

atomic number of five, called boron-If).

AHow Can We Use X Information About Isotopes?

Z

Z tells us how many protons there are, and because there are always the same number of protonsas electrons, we know the number of electrons too. For example, ~1 B has an atomic number offive so it also contains five electrons in addition to its five protons. How can we tell how manyneutrons are in an isotope? The mass number, A, for boron eleven is eleven. This means that thenumber of protons and neutrons adds up to eleven. From the atomic number we know that fiveof the eleven are protons. Therefore the rest of the mass number must be neutrons. A minus Zequals number of neutrons. Eleven minus five equals six.

4.8 INTRODUCTION TO THE PERIODIC TABLE

The periodic table has lots of information useful to a chemist. Let's see what kind of basicinformation you can get from the periodic table now, and ill later chapters, you will see that theperiodic table contains even more useful inforniation.

What Basic Information Is in the Periodic Table?

The table is divided up into boxes, each of which contains the one or two letter symbol for anelement. Every element has a place in the periodic table. There are usually numbers writtenabove and below each of the symbols. The periodic table below has been simplified to showonly one set of numbers, written above the element symbols. The numbers represent the atomicnumber, the number of protons (and the number of electrons) for each element. As you movefrom left to right along the periodic table, the atomic number of subsequent elements increasesby one. When you reach the end of a row, if you move to the beginning of the next row, theelements again begin increasing in atomic number by one. When the elements are arranged inthis way, it's possible to group elements with similar properties together in columns, which areoften called families. For example, the elements He, Ne, Ar, Kr, Xe, and Rn, called the noblegases, all have similar properties. They are all gases which do not tend to combine with other

Chapter Review 67

elements to produce compounds. Many of the columns, or groups, have numbers. Thesenumbers are always written along the top of the periodic table. The first group (group 1) on theleft side of the periodic table is called the alkali metals, and the second (group 2), the alkalineearth metals. The group with the unreactive elements He, Ne, AI, Kr, Xe and Rn is numberedgroup 8.

noblegases

halogens ~~ 8

alkalineearthmetals

1 ~I'" ........ I--

1 atomic -w 2H 2 number Fe 3 4 5 6 7 He3 4 5 6 7 8 9 10Li Be B C N 0 F Ne

11 12transition metals

13 14 15 16 17ANa M~ / "Al Si P S ci Ar19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr

37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54Rb Sr Y Zr Nb Mo Tc Ru Rh Pd A~ Cd In Sn Sbtltl I Xe55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 8 85 86Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi P At Rn87 88 89 104 105 106 107 108 109

...... Fr I Ra I Ac Unq Unp Unh Uns Uno Une

58 59 60 61 62 63 64 65 66 67 68 69 70 71Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu90 91 92 93 94 95 96 97 98 99 100 101 102 103Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

actinides

lanthanides

aIkaI

metaIs

On the right side of the periodic table is a heavy jagged line running from the top to the bottomof the table. This line separates elements which are nonmetals from those which are metals. Themetals lie on the left side of the jagged line, and the nonmetals on the right. There are manymore metals than nonmetals. Many of the metals in the short columns in the middle of the tableare called transition metals. Metals can be distinguished from nonmetals by the followingcharacteristics. Metals appear shiny. They conduct both heat and electricity. They can be pulledinto wire without crumbling or breaking, and can be beaten into thin sheets.

The elements to the right of the jagged line are the nonmetals. The nonmetals do not have a fixedset of characteristics. Their properties are more variable than the metals.

68 4 Chemical Foundations

There are some elements which lie right on the jagged line which separates metals fromnonmetals. These elements have some of the properties of both metals and nonmetals. They areboron, B; silicon, Si; germanium, Ge; arsenic, As; antimony, Sb; and tellurium, Te and are oftencalled metalloids, or semi-metals.

4.9 NATURAL STATES OF THE ELEMENTS

How Are the Common Elements Normally Found in Nature?

Only a few elements found in nature are not combined with other atoms. Those few elementsinclude the noble gases and some of the metals, such as gold, silver andplatinum.

Some elements are commonly found in nature as diatomic molecules, that is, two atoms of thesame element combined to form a molecule. The nitrogen found in the atmosphere is present asNz molecules, and oxygen is found as Oz. Hydrogen gas, although not usually present in theatmosphere, exists as molecules ofHz.

The halogens, including fluorine, chlorine, bromine and iodine, when present as free elementsalso exist as the diatomic molecules Fz' Clz' Brz and Iz.

Metals are found neither as single atoms, nor as diatomic molecules. Rather, they exist as largeclusters of atoms.

At room temperature there are two liquid elements, the metal mercury, and the halogen bromine.Several elements are gases at room temperature- Hz, 0z' Nz' Fz' and Clz' and the noble gases. Allthe other elements are solids at room temperature.

The structures of the nonmetal solids do not fall into any easily described categories.

4.10 IONS

What Are Ions and How Do They Form?

An ion is formed when an atom with equal numbers of protons and electrons either loses or gainselectrons. The number of protons remains the same. The ion which is formed has either anexcess or a deficiency of electrons, which means it has one or more positive or negative charges.

A cation is an ion with one or more positive charges. Cations form when atoms lose electrons.For example, a potassium atom has nineteen protons and nineteen electrons. Potassium forms acation when the potassium atom loses an electron. The cation has nineteen protons and eighteenelectrons, one fewer electron than protons. So the potassium cation has a 1+ charge.

Chapter Review 69

An anion is an ion with one or more negative charges. Anions form when atoms gain electrons.For example, a sulfur atom has sixteen protons and sixteen electrons. An anion of sulfur formswhen sulfur gains two electrons. The anion which forms has sixteen protons and eighteenelectrons. So the sulfur anion has a 2-charge.

How Can the Periodic Table Tell You the Charge on an Ion?

The periodic table is organized so that the group number also helps you know the charge on theion. This relationship works for elements in groups 1, 2, and 3. Elements in group 1 formcations with a 1+ charge, those in group 2 form cations with 2+ charge, group 3 elements formcations with 3+ charge. Elements in group 6 form anions with a 2- charge, and group 7 elementsform anions with 1-charge. Elements which are not in groups 1, 2, 3, 6, or 7 either do not formions, or the charge on the ion varies.

4.11 COMPOUNDS THAT CONTAIN IONS

How Can We Show That Compounds Contain Ions?

Not only can atoms form ions, compounds exist which are made of ions. Chemists believe thatcompounds such as sodium chloride are made of sodium ions with a 1+ charge, and chloride ionswith a 1-charge. Solid sodium chloride does not conduct an electric current, but molten sodiumchloride and sodium chloride dissolved in water do. It is believed that movement of the ions isnecessary for an electric current. The ions in solid sodium chloride are not able to move aroundbecause solids have a very rigid structure, and thus there is no electric current. With moltensodium chloride, or sodium chloride dissolved in water, ions are free to move around. Themovement of atoms or ions in liquids is much greater than it is in solids, so the ions are free tocarry an electric current. Pure water does not carry an electric current because the oxygen andhydrogen in water do not produce ions.

How Do Ions Combine to Produce Compounds?

Compounds made from ions must have a net charge of zero. That is, the positive charge must beequal to the negative charge. This means that compounds must contain both cations and anions.A compound made from ions of potassium and sulfur is an example. Potassium in group 1 of theperiodic table forms cations with 1+ charge, K+. Sulfur in group 6 forms anions with 2- charge,SZ-. When potassium and sulfide ions combine, there must be enough potassium and sulfide ionsso that the net charge on the compound is zero. If one potassium ion combined with one sulfideion, the net charge on the compound would be 1-, because the 2- charge on the sulfide ion is notcompletely offset by the 1+ charge on the potassium ion. In order for the compound to have nonet charge, two potassium ions must combine with one sulfide ion, KzS. This rule must befollowed when writing formulas for all ionic compounds.

70 4 Chemical Foundations

LEARNING REVIEW

1. This review question can help you to determine your progress with the material in Chapter4. You should be able to answer each of the questions below for the common elementslisted in Table 4.3 of the textbook. Answer each question below for the elementsymbolized by Br.

a. What is the name of the element?b. In which group of the periodic table is it found?c. What is its family name?d. When found in nature uncombined with other elements, what is its state?e. At room temperature, what is its physical state, solid, liquid, or gas?f. What is the name and charge of the ion it forms?g. How many neutrons are found in this isotope, ~~Br ?

2. Which of the ten most abundant elements (determined by mass percent) on earth are notfound in large amounts in the human body?

3. Match the elements below with the correct description.

oxygensiliconcarbontitaniumhydrogen

molybdenum

most abundant element on earthmost abundant element in the human bodytrace element in human body25.7 % of mass on earththese three elements make up 93% of massin the human bodyless than 1% of the mass on earth

4. Write symbols for the following elements.

a. arsenic f. leadb. fluorine g. potassiumc. magnesium h. chromiumd. iron i. nitrogene. neon j. calcium

5. Which of the common elements in Table 4.3 of your textbook have a one-letter symbol?

Learning Review 71

6. Some of the element symbols are not related to the modern name of the element. What arethe elements represented by the following element symbols?

a.b.c.d.

WHgCuK

e.f.g.h.

FePbSbNa

7. Match the element name with the correct element symbol.

cadmium Clcarbon Crcalcium Cchlorine Cocobalt Cucopper Cdchromium Ca

8. Match the element symbol with the correct element name.

Na silverSr sulfurS sodiumAg siliconSi strontium

9. Describe the main parts of Dalton's atomic theory.

10. How does Dalton's atomic theory relate to the law of constant composition?

11. Dalton's model became more widely accepted when the existence of NO, N02, and N20

became known. What aspect of Dalton's model allowed Dalton to predict the existence ofthese compounds?

12. Write chemical formulas for the following compounds.

a. ethyl alcohol, which contains 2 carbon atoms, 6 hydrogen atoms, and 1 oxygen atomb. a compound which contains 1 atom of magnesium and 2 atoms of brominec. a compound which contains 4 atoms of phosphorus and 10 atoms of oxygend. a compound which contains 1 atom of arsenic and 3 atoms of hydrogen

72 4 Chemical Foundations

13. What is the total number of atoms found in each of the following compounds? What is thetotal number of elements found in each?

a. KOHb. NZ03

c. CCl4d. Hz°ze. N~P04

14. A physicist named J. J. Thomson showed that all atoms can be made to emit tiny particleswhich are repelled by the negative pole of an electric field. Which subatomic particle wasthis evidence for?

a. protonb. neutronc. electrond. nucleuse. isotope

15. Match the scientist with the discovery.

Ernest Rutherford1. 1. ThomsonLord KelvinRutherford & Chadwick

demonstrated the existence of electronsdemonstrated the existence of neutronsdeveloped the plum pudding model of the atomdeveloped the nuclear atom model from gold foilexperiments

16. Label the parts of the experimental apparatus used to develop the model of the nuclearatom.

Learning Review 73

17. In the gold foil experiment. how did Rutherford interpret each of the followingobservations?

a. Most of the a-particles traveled unimpeded through the foil.b. Some of the a-particles were deflected slightly from the straight path when they

entered the foil.c. A few of the a-particles bounced back when they entered the foil.

18. Fill in the missing relative masses and relative charges for each of the subatomicparticles.

Relative mass Relative chargea. Electron 1-b. Proton.c. Neutron 1839

19. Is the following statement true or false? An isotope of sodium could contain 12 protons.12 neutrons and 11 electrons,

20. Label the parts of the symbol below.

Ax

z

A21. Write the symbols for the isotopes below in X notation.

Z

a. An isotope of hydrogen has an atomic number of 1. and a mass number of 3.b. An isotope of chlorine. has an atomic number of 17 and a mass number of 37.c. An isotope of oxygen has 8 protons and 10 neutrons.d. An isotope of uranium has 92 electrons and 143 neutrons.e. An isotope of sulfur has an atomic number of 16 and 16 neutrons.

22. An isotope of titanium contains 24 neutrons and has a mass number of 46.

a. How many protons does it contain?b. How many electrons does it contain?

23. Aluminum-29 has an atomic number of 13.

a. What is its mass number?b. How many neutrons does it have?

74 4 Chemical Foundations

24. Match the group name on the left with an element found in that group.

halogen Catransition metal Nealkali metal Fealkaline earth metal Knoble gas F

25. Fill in the boxes of the periodic table with element symbols for each of the families below.The number at the top of each box represents atomic number.

a. halogens

9

17

35

53

b. alkaline earth metals

12

20

38

56

c. noble gases d. alkali metals

2 3

10 11

18 19

36 37

54

26. Which of the following elements are nonmetals?

a.b.c.

AlCCr

d.e.f.

p

BrI

Learning Review 75

27. Some of the elements along the jagged line on the right side of the periodic table haveproperties of both metals and nonmetals. Fill in the elemental symbols for thesemetalloids.

C

Al

Po At

28. Some elements exist in nature as diatomic molecules. Which of the elements below willbe found as diatomic molecules?

a. Ar e. Sb. 0 f. Nc. K g. Hd. F h. Cl

29. At room temperature, what is the physical state (solid, liquid, or gas) of each of theelements which naturally form diatomic molecules?

30. Which elements are always found in nature as individual atoms?

a. carbon e. heliumb. krypton f. neonc. magnesium g. aluminumd. chlorine h. sulfur

31. Fill in the name of the correct element next to its description at 25°C.

76

a.b.c.d.e.f....

Liquid metalYellow green gasColorless gasA 2 carat diamondA reddish brown liquidDark purple solid

4 Chemical Foundations

32. Balance the equations for the formation of cations from neutral atoms.

a. Ca ---.... -- +--b. K ---.... +-- --c. Sr ---.... -- +--d. Rb---"" -- +--

33. Balance the equations for the reactions of cations with electrons.

a. Mg2+ + ---....b. Li+ + ---....c. 2H+ + ---....d. Na+ + ---....

34. Fill in the correct number of protons and electrons for either the element or the ion in thetable below.

element protons electrons ion protons electrons

potassium 19 19oxygen 8 10bromine 35 36strontium 38 38aluminum 13 10

35. You wish to fmd out whether the compound MgF2 is composed of ions. What test could

you perform to help you make a decision?

36. a.b.c.

Which diagram represents a solid NaCI crystal?Which diagram represents NaCI dissolved in water?Which form of NaCI, solid or aqueous solution, allows free movement of ions?

i. ii.

37. How many of each ion is needed to form a neutral compound?

a. Ca2+ andF e. Sr2+ and crb. Mg2+ and 0 2- f. K+ and p3-

c. Na+ and S2- g. Na+ and N3-

d. Li+andr

Learning Review 77

38. What is wrong with the formulas below? Write the correct formula for each.

a.b.c.

d.e.f.

ANSWERS TO LEARNING REVIEW

1. a. bromineb. group 7c. halogensd. Brze. liquid

f. bromide ion, Br"g. 45

2. Silicon, aluminum and iron are found in large amounts on earth, but in small amounts inthe human body.

3. Note that some of the elements are found in more than one category.

oxygen ..:::::::~-_... most abundant element on earth

silicon most abundant element in the human body

trace element in the human body

25.7% of mass on earth

-"'~-iiiii'IIIIIIthesethree elements make up 93% of themass in the human body0.58 % of the mass on earth

4. a. Asb. Fc. Mgd. Fee. Ne

f. Pbg. Kh. Cri. Nj. Ca

5. Boron, carbon, fluorine, iodine, nitrogen, oxygen, phosphorus, potassium, sulfur, tungstenand uranium all have one-letter symbols.

78 4 Chemical Foundations