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Patterns among the ElementsBy the 1780s, chemists wondered why some elements, such asoxygen, were gases, while others, such as gold, were metals. Tocomplicate matters, by the 1860s, the list of known elements hadgrown to 63. No one knew if that list included all the elementsthat existed or whether there were hundreds or even thousandsmore that were still undiscovered. Many chemists continued tosearch for a unifying pattern among the elements.
Then, in 1867, Russian chemist and teacher DmitriMendeleev (1834–1907) found the pattern (Figure 5.32). He didit by gathering all the information that he could about the knownelements and writing it down on cards, using one element per card(Figure 5.33). The information included properties such asestimates of the mass of the atoms of each element, colour,density, melting point, and what each element did or did not reactwith. He then sorted the cards into rows and columns, based onsimilarities in the elements’ properties. This arrangement of cardsformed a table, as shown in Figure 5.32. Within Mendeleev’stable, and for the first time in history, a complete pattern of theelements emerged.
188 UNIT B Atoms, Elements, and Compounds
Here is a summary of what youwill learn in this section:
• The periodic table organizesthe elements by theirproperties, such as the mass ofeach element’s atoms and theelement’s melting point.
• Atomic number is the numberof protons in an atom anduniquely identifies an element.
• Bohr diagrams of the first 20elements of the periodic tablereveal important patterns thatrelate to the elements’properties.
The Periodic Table
H = 1
Li = 7
Be = 9, 4 B = 11 C = 12 N = 14 O = 16 F = 19 Na = 23
Mg = 24 Al = 27,4 Si = 28 P = 31 S = 32 Cl = 35, 5 K = 39 ? = 45 ?Er = 56 ?Yt = 60 ?In = 75, 5
Ti = 50 V = 51 Cr = 52 Mn = 55 Fe = 56 Ni = Co = 59 Cu = 63,4 Zn = 65,2 ? = 68 ? = 70 As = 75 Se = 79,4 Br = 80 Rb = 85,4 Sr = 87,5 Ce = 92 La = 94 Di = 95 Th = 118?
Zr = 90 Nb = 94 Mo = 96 Rh = 104,4 Ru = 104,4 Pl = 106,6 Ag = 108 Cd = 112 Ur = 116 Su = 118 Sb = 122 Te = 128? I = 127 Cs = 133 Ba = 137
? = 180. Ta = 182. W = 186. Pt = 197,4 Ir = 198. Os = 199. Hg = 200. Au = 197? Bi = 210 Tl = 204 Pb = 207
Figure 5.32 Dmitri Mendeleev arranged the elements according to certain properties.
5.3
Figure 5.33 Mendeleev gatheredinformation on each known elementand wrote it on a card.
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A Table Based on PropertiesIn Mendeleev’s table, all the cards representing metals ended upon one side, and all the non-metals ended up on the other.Metalloids were in the middle. Even most of the elements thatwere gases at room temperature were grouped together.Mendeleev was on to something.
Mendeleev knew that some elements were very similar, and itmade sense to him to group them together (Figure 5.34). Forexample, he grouped together sodium, lithium, and other metalsthat reacted violently with water. Mendeleev had so muchconfidence in his arrangement that he left a gap in his table if hecould not find an element with the right properties to put in acolumn. The gap represented an element that was yet to bediscovered. Other chemists were doubtful.
Then, in 1886, the element germanium was discovered. Itsproperties were an exact match of the properties predicted for amissing element in Mendeleev’s table. After that, other scientistswere convinced that Mendeleev had it right. Today, we use a tablebased on Mendeleev’s table called the periodic table of theelements.
189The periodic table organizes elements by patterns in properties and atomic structure.
B15 Quick Lab
Exploring the Periodic Table
Your teacher will provide you with a copy of theperiodic table. Within the periodic table, you will lookfor patterns among the elements’ properties.
PurposeTo become familiar with the periodic table
Procedure
1. Find the element boron (B) and shade it in.Then, with the same colour, shade in all elementsthat make a diagonal below and to the right ofboron, starting with silicon (Si). Finally, shade in germanium (Ge), antimony (Sb), and polonium (Po). These elements are the metalloids.
2. All the elements to the left of the metalloids, excepthydrogen, are metals. All the elements to the rightof the metalloids are non-metals. Label the metalsand non-metals, but do not shade them.
3. All the elements in the farthest left column, excepthydrogen, react violently with water. Shade themthe same colour, and label them “alkali metals.”
4. All the elements in the column to the right of thealkali metals are slightly less reactive than thealkali metals. Shade them another colour, andlabel them “alkaline earth metals.”
5. Find column 17, and shade all the elements in itthe same colour. Label the column “halogens.”Find column 18, and shade those elements theirown colour. Label them “noble gases.”
Question
6. Why does it make sense to colour columns ratherthan rows?
Materials & Equipment• a periodic table
• pencil crayons or highlighters
Figure 5.34 Dmitri Mendeleev wasthe first to create a table thatlogically organized all the elements,including those undiscovered at thetime.
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The Modern Periodic TableFigure 5.36 on the next page shows the periodic table of theelements. The periodic table is a chart that places all of theelements in rows and columns. In the modern periodic table,elements are listed from left to right and top to bottom accordingto a property called atomic number.
Atomic NumberAtomic number is the number of protons in an atom of anelement. The lowest atomic number is 1, which is the atomicnumber of the element hydrogen (H) (Figure 5.35). This meansthat every hydrogen atom has one proton in its nucleus.Hydrogen is placed in the top row and farthest left column of thetable. The next element in the periodic table is helium (He),which has atomic number 2. All helium atoms have two protons.Another way to look at it is that any atom with two protons mustbe a helium atom.
Moving down to the next row and back to the farthest leftcolumn, the element with atomic number 3 is lithium (Li).Atomic number increases by one with each consecutive element.This increase continues though the entire table until the atomicnumber is well past 100. No one knows what the highest possibleatomic number is, but as of 2009 it was 118.
190 UNIT B Atoms, Elements, and Compounds
H atom
1p
He atom
2p2n
Figure 5.35 A hydrogen atom hasone proton, and a helium atom hastwo protons.
Learning Checkpoint
1. Use the periodic table to find the atomic number of each of the followingelements.
(a) C (b) O (c) Na (d) Si
(e) S (f) Cl (g) Fe
2. How many protons are in an atom of each of the following elements?
(a) lithium (b) nitrogen (c) fluorine
(d) aluminum (e) copper (f) gold
3. Name the element with the following number of protons.
(a) 1 (b) 2 (c) 10 (d) 19
(e) 20 (f) 31 (g) 47
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191The periodic table organizes elements by patterns in properties and atomic structure.
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ist9_ch05.qxd 7/21/09 2:51 PM Page 191
Atomic Mass and Ion ChargeEach element has its own square on the periodic table. Theinformation given in the square is not always the same ondifferent versions of the periodic table, but the element’s name,symbol, and atomic number are almost always given. Figure 5.37,taken from the periodic table on the previous page, shows twoother pieces of information: atomic mass and ion charge.
Atomic MassAtomic mass is the average mass of an element’s atoms. Atomicmass is given in atomic mass units (amu). As Figure 5.37shows, the atomic mass of iron is 55.85 amu. From the periodictable, we can see that the atomic mass of hydrogen is 1.01 amu.This means that iron atoms are about 55.85 times heavier thanhydrogen atoms, which are the least massive of all atoms.
Atomic masses are always expressed as decimal fractions. Onereason that they do not have whole number values is that, exceptfor fluorine, atoms of the same element have different numbers ofneutrons. For example, the most common type of hydrogen atomhas one proton and one electron but no neutron. A smallpercentage of hydrogen atoms have one proton, one electron, andone neutron, and an even smaller percentage have one proton,one electron, and two neutrons. Recall that most of an atom’smass comes from its protons and neutrons. For this reason,hydrogen atoms with different numbers of neutrons havedifferent masses. The atomic mass of hydrogen is an average ofthese masses.
Notice that atomic mass generally increases in order of atomicnumber. There are a few exceptions to this pattern. For example,iodine (I) has a lower atomic mass than tellurium (Te).
Ion Charge Ion charge is the electric charge that an atom takes on when itloses or gains electrons. An atom or group of atoms that has lostor gained electrons is called an ion. Metal atoms can loseelectrons in certain situations. Electrons have a negative charge,and so an atom that loses electrons becomes a positive ion. Forexample, if an iron atom loses three electrons, it becomes an ionwith a 3+ charge (Figure 5.38). If an iron atom loses twoelectrons, it becomes an ion with a 2+ charge.
192 UNIT B Atoms, Elements, and Compounds
Fe26
atomicnumber
atomic mass
ion charges
3+2+
55.85
iron
Figure 5.37 Information from theperiodic table about iron (Fe)
Fe
3e
Fe3+
Figure 5.38 When an iron atomloses electrons, it becomes apositive ion.
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Elements with atoms that can form similar ions are groupedtogether in the periodic table. Metals generally lose electrons andbecome positive ions. Many non-metals can gain electrons and sobecome negative ions.
Some elements do not form ions. Helium, for example, doesnot normally form ions. For these elements, no ion charges areshown in their squares in the periodic table.
Periods and Chemical FamiliesThe periodic table has seven horizontal rows. Each of theserows is called a period. A number written on the left side ofthe table identifies each period. For example, hydrogen andhelium are in Period 1. Potassium is the first of 18 elements inPeriod 4.
There are 18 vertical columns in the periodic table, and eachrepresents a different group (also called a chemical family).The elements within a group share certain physical andchemical properties. Each group has its own number, written atthe top of the periodic table. For example, the element carbon(C) is in Group 14. It is also common to refer to a group by thefirst element in it. Group 14 is also called the carbon group.Some groups have special names (Figure 5.39). We will discussthree of these very important groups in more detail:
• alkali metals• halogens• noble gases
193The periodic table organizes elements by patterns in properties and atomic structure.
H1
12
Li3
Na11
K19
Rb37
Ca55
Fr87
Be4
Mg12
Ca20
Sr38
Ba56
Ra88
F9
Cl17
Br35
I53
At85
He2
Ne10
Ar18
Kr36
Xe54
Rn86
AlkalineEarthMetals Halogens
Groups3 - 16
NobleGases
AlkaliMetals
17
18
Figure 5.39 Four groups in theperiodic table known by specialnames
Learning Checkpoint
1. Use the periodic table to find the atomic mass for each of the followingelements.
(a) H (b) He (c) N (d) F (e) S (f) Ca (g) Ag
2. Name the element with the following atomic mass.
(a) 12.01 amu (b) 16.00 amu (c) 39.10 amu (d) 83.80 amu
3. What is the electric charge on an ion of each of the following elements?
(a) Li (b) Be (c) N (d) S (e) Al (f) I
4. Although the element hydrogen is a non-metal, it is located on the left sideof the periodic table. Explain how placing hydrogen in this position relatesto its ion charge.
5. Describe the patterns in atomic masses and ion charges in the periodictable.
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Properties within GroupsWhen we compare the physical properties of elements withingroups, a number of patterns become clear. Refer to the periodictable on page 191 as you read about these patterns.
Alkali Metals (Group 1): Li, Na, K, Rb, Cs
• Similarities: All of these metals are silver-grey in colour(Figure 5.40). Like other metals, they are malleable andductile, and they conduct electricity and heat. However,compared to other metals, the alkali metals have lowmelting points. They all melt below 170°C, a temperatureeasily achieved by most ordinary kitchen ovens. They are allsoft enough to cut with a knife. In addition, they all reacteasily with water and air.
• Differences: There is a gradual change in the physicalproperties in this group from the first element, at the top,through to the last, at the bottom. Moving from lithium tocesium, there is a regular increase in density. The elementsalso get softer and easier to cut. Lithium’s melting point is170°C, while potassium’s is 64°C. Cesium’s melting point isjust 28°C.
Halogens (Group 17): F, Cl, Br, I
• Similarities: All of these elements are non-metals. Each hasa noticeable colour. Although bromine is a liquid and iodineis a solid at room temperature, with slight heating they formgases, like the other halogens. All are very reactive, andchlorine, bromine, and iodine can be used as disinfectants.
• Differences: From fluorine, the first element in the group,down through to iodine, the colours of the halogens grow inintensity (Figure 5.41). Their melting points also graduallyincrease from –219°C for fluorine to 113°C for iodine.
194 UNIT B Atoms, Elements, and Compounds
Figure 5.40 Alkali metals
Figure 5.41 The halogens. From left to right: fluorine, chlorine, bromine, and iodine
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Noble Gases (Group 18): He, Ne, Ar, Kr, Xe, Rn
• Similarities: Although all exist naturally as colourless gases,these elements will glow with bright colours if an electriccurrent is passed through them, as in a neon light (Figure5.42). None of these gases is chemically reactive except incertain special situations.
• Differences: The density of the gases increases steadilymoving from helium through to radon. Balloons filled withhelium or neon will rise in the air, with helium balloonsrising faster than neon balloons. Argon balloons sink slowlyin air. Balloons filled with krypton, xenon, or radon wouldsink quite quickly in air, with radon balloons sinking thefastest.
195The periodic table organizes elements by patterns in properties and atomic structure.
Figure 5.42 This lighted glass sculpture of a sea anemone contains noble gases. As an electric current runs through the gases, they light up, each with a different colour. Some of thegases are denser than the others, making the sculpture different colours in different areas.
Learning Checkpoint
1. Give the names and symbols for the elements found at these locations inthe periodic table.
(a) Period 3, Group 1 (b) Period 2, Group 13
(c) Period 4, Group 11 (d) Period 5, Group 17
2. Give the period and group for each of the following elements.
(a) Mg (b) Si (c) Cl (d) He (e) Au (f) Pb
3. Compare and contrast the physical properties of different alkali metals.
4. Compare and contrast the chemical and physical properties of thehalogens and the noble gases.
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During Reading
Fixing Up UnderstandingUsing Key Words
As you read, identify the keywords and write them in yournotebook. Look at the keywords, and try to restate whatyou read using the words ascues. Talk with a partner tocompare what each of youunderstood from what you read.
Atomic Theory Supports the Periodic TableMendeleev created his periodic table long before studies of atomicstructure revealed the arrangements of subatomic particles. As aresult, Mendeleev did not know about atomic number, which isused to order the elements in the modern periodic table. Instead, heused atomic mass. Similarly, he did not know about electrons ortheir arrangements within atoms. When electron arrangements areconsidered, it makes Mendeleev’s work all the more remarkable.
Chlorine: A Typical AtomAtoms of all elements have the same basic structure but differentnumbers of protons, neutrons, and electrons. Chlorine is anexample. The element chlorine is used as a disinfectant inswimming pools and to purify drinking water. A diagram of anatom of chlorine is shown in Figure 5.43 on the next page. Noticethat the number of protons and the number of electrons are equal.This is true of all atoms.
The NucleusThe nucleus, shown at the centre of the chlorine atom, and alsoenlarged, is a tiny part of the atom that contains protons andneutrons gathered together into a ball. The nucleus contains onlya small part of an atom’s total volume. Depending on the atom,the region outside the nucleus of an atom is 10 000 to 50 000times the diameter of the nucleus.
• All chlorine atoms have 17 protons. Each proton has a chargeof 1+, so the total positive charge in the nucleus is therefore17+.
• Different kinds of chlorine atoms can have differentnumbers of neutrons. It is the number of protons in anatom that determines what element the atom is, not thenumber of neutrons. The most common types of chlorineatoms have 18, 19, or 20 neutrons.
• The nucleus contains 99.99% of the mass of the atombecause protons and neutrons have much greater mass thanelectrons.
196 UNIT B Atoms, Elements, and Compounds
Suggested Activity •B17 Quick Lab on page 200
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ElectronsElectrons exist in shells, or energy levels, surrounding the nucleus.The innermost shell can hold a maximum of two electrons. Eachof the next two shells can hold up to eight. Electrons often exist inpairs.
• Electrons occupy more than 99.99% of an atom’s volume.
• Electrons can move between energy levels.
• The outermost shell that has electrons in it is called thevalence shell. Electrons in this shell are called valence electrons. Other shells containing electrons are called inner shells, and the electrons in them are called innerelectrons. The properties of elements are strongly affected bytheir valence electrons.
Early researchers of the atomwere surprised at first to discoverthat when a shell becomes morethan half-filled, the electrons begin to pair up, as shown in Bohr diagrams. Even though the negatively charged electronsrepel each other, pairing helpselectrons to get closer to thepositive protons in the nucleus.Friedrich Hund (1896–1997), aGerman physicist, was the first towork out how electron pairingoccurs (Figure 5.44).
197The periodic table organizes elements by patterns in properties and atomic structure.
Figure 5.43 (a) A Bohr diagram of a chlorine atom, which contains 17 protons and 17electrons. The number of neutrons varies between chlorine atoms. (b) A diagram of thenucleus of a chlorine atom
neutron proton
chlorine atom
nucleus
valence shell
valence electron
inner shells
inner electron
Figure 5.44 Physicist Friedrich Hund
(a) (b)
Suggested STSE Activity •B18 Decision-Making Analysis CaseStudy on page 201
ist9_ch05.qxd 7/21/09 2:51 PM Page 197
People have used various shapes, colours, andarrangements to organize theelements in meaningful ways.Some are shown on the next page.Go to ScienceSource to start yoursearch for different versions of theperiodic table.
Take It Further Patterns in the Arrangements of Electrons Figure 5.45 shows Bohr diagrams for the first 20 elements of theperiodic table. As you examine the Bohr diagrams, look carefullyat the electrons in the outer shells. A very important pattern inthe arrangement of electrons is that elements in the same grouphave the same number of valence electrons. Notice, in particular,the following points:
• Group 1: Atoms of hydrogen, lithium, and sodium eachhave one valence electron. Although hydrogen is not in thesame group as the alkali metals, it does share some chemicalproperties with them because of their similar valenceelectron arrangements. For example, they can all form ionswith a 1+ charge.
• Group 18: A helium atom has only two valence electrons,which is the maximum number for the first energy shell.Atoms of neon and argon each have eight valence electrons,the maximum number for the second and third shells. Thenoble gases share many properties because their atoms allhave filled valence shells.
The number of valence electrons is not only related to thephysical properties of a group of elements. The number of valenceelectrons is also related to the ways in which atoms of elementscombine to form compounds.
198 UNIT B Atoms, Elements, and Compounds
K4
Na3
Li2
H1
1
19
11
3
1
Ca
Mg
Be
2
20
12
4
18
13 14 15 16 17
Al
B
13
5
Si
C
14
6
P
N
15
7
S
O
16
8
Cl
F
17
9
Ar
Ne
He
18
10
2
Figure 5.45 A segment of the periodic table showing electrons arrangements for the first 20 elements
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Organizing the Periodic Table in Different Ways Scientists continue to organize the elements in different ways.Dr. Theodor Benfey, a U.S. chemist, suggested a spiral version ofthe periodic table (Figure 5.46). In Dr. Benfey’s periodic table, theelements are shown in an unbroken series, starting withhydrogen and radiating outward. Figure 5.47 shows anotherperiodic table, known as the physicist’s periodic table. Thisperiodic table is three-dimensional and groups the elementsaccording to the energy levels of their electrons.
199The periodic table organizes elements by patterns in properties and atomic structure.
Rn
Xe
Kr
Ar
NeHe Li
Na
K
Rb
CsRo
Ac
ThPa
U
Nd
NpPu
AmCm
Gd Tb
Dy
Ho EsEr Fm
Tm MdYb
Lu Lr
HfDb
TaJl
W
Rf
BhRe
HnOs
Mt
Ir
110
Pt
111
Au
112
Hg RhPd
AgCd Co
NiCu
Zn
CrV
TiSc Mo
Mn Tc
Fe
Ru
NbZr
Y
No
Bk
CfEu
Pm
Sm
PrCe
La
Ba
Sr
Ca
MgBe
BH
AI
Ga
In
TI
Pb
Sn
Ge
Sip
As
Sb
Bi
AtI
BrCl
F
Po TeSe S O
N C
Fr
Figure 5.46 Dr. Benfey’s periodic table
Learning Checkpoint
1. Give the number of valence electrons in an atom of each of the followingelements.
(a) hydrogen (b) aluminum (c) carbon (d) oxygen (e) chlorine
2. For each of the following groups of elements, give the number or numbersof valence electrons in the atoms.
(a) Group 1 (b) Group 2 (c) Group 15 (d) Group 18
3. (a) What is similar about the valence electrons for atoms of elements in Period 2?
(b) What is similar about the valence electrons for atoms of elements in Period 3?
4. At room temperature, oxygen is a colourless gas and sulphur is a yellowsolid. Why are they in the same group in the periodic table?
H H e
M n F eP S
N a M gA l
C rS iU
T i A r
C oC l N i
C uS c Z n
N s M tB i P o
C s B aT i
S qP bH a
R f R n
1 1 0A t 1 1 1
1 1 2A c 1 1 3
G d T bT c R u
A s S eK C a
G a K rY
E uM o
G eZ r
S mN bP m
N dP r C d
D yR h
B rA q
H oP d E r
T mY b
C e L uC m B k
R e O sS b T e
R b S rI n X e
L a
A mW
S nH f
P uTaN p
UP a H g
C fI r
IA u
E sP t F m
M dN o
T h L r
N OL iC B e
B N eF
1 2 0 1 2 1
1 1 6 1 1 7F r1 1 5 R a
1 1 4 1 1 91 1 8
n=1
n=2
n=3
n=4
n=5
n=6
n=7
n=8
– m
– s
+ mn
+ s
s p d f
Figure 5.47 The physicist’s periodic table
Suggested Activity •B19 Inquiry Activity on page 202
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200 UNIT B Atoms, Elements, and Compounds
B17 Quick Lab
In this activity, you will practise drawing Bohrdiagrams of atoms and ions of different elements.
PurposeTo practise drawing Bohr diagrams of atoms and ions
Procedure
1. Find hydrogen on the periodic table. Begin aBohr diagram of a hydrogen atom by writing“1p” to show that there is one proton in itsnucleus. Draw a circle to represent the nucleus.
2. Draw the energy shell around the nucleus aswell as the valence electron.
3. Find lithium on the periodic table. Begin a secondBohr diagram. Write down the number of protonsin the nucleus of a lithium atom, and draw theenergy shells and electrons in each shell.
4. Look up the charge on a lithium ion in a periodictable. Draw a Bohr diagram of a lithium ion.
5. Find sodium on the periodic table. Draw a Bohrdiagram of a sodium atom.
Questions
6. How many protons and electrons would beshown in a Bohr diagram of a helium atom?
7. How is a Bohr diagram of a lithium atomdifferent from a Bohr diagram of a lithium ion?
8. Describe the similarities and differences amongthe energy shells in your Bohr diagrams forlithium and sodium.
Drawing Bohr Diagrams
B16
Working with Toxic Elements
In the 18th and 19th centuries, mercury wasused in hat making. The mercury produced toxicvapours, which caused symptoms of mercurypoisoning in the hat makers and in people whowore the hats. Mercury poisoning could impairvision, speech, hearing, or balance as well ascause mood swings and memory loss. The “MadHatter” from Lewis Carroll’s classic fantasy booksabout Alice in Wonderland was a cartoon versionof a hatter (hat maker) affected by mercurypoisoning. Today, laws restrict how mercury canbe used.
Other people who work with toxic elementsinclude scientists who study radioactive elements,painters, and pottery makers. Some of the metalsthat give paints and pottery glazes their brightcolours include toxic cobalt, lead, and cadmium.
1. In order to protect the health of workers,how could workplaces limit the use of toxicelements?
2. What types of restrictions would you considerfor artists working with toxic elements in theirown homes? What questions would you needto answer in order to write a set of guidelinesfor artists?
3. What steps can people take to work safelywith toxic elements?
4. If removing toxic elements from Earth’ssurface will contaminate the environment,should we do this? What restrictions, if any,would you place on mining for toxicelements? Justify your response.
Science, Technology, Society, and the EnvironmentSTSE
Materials & Equipment• a copy of the periodic table
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CASE STUDY
201The periodic table organizes elements by patterns in properties and atomic structure.
IssueDue to environmental pollution, the concentration ofheavy metals in fish is on the rise. For people whoeat a lot of fish, heavy metal contamination is aserious concern.
Background InformationMany metals are necessary for human health. Forexample, iron is so important in the diet that somepeople need to take iron supplements. However, theheavy metals, including cadmium, mercury, andlead, are toxic.
Heavy metal pollution results mainly fromindustrial processes, such as refining ores, burningfuel, and using nuclear energy. Heavy metals arealso used in some types of batteries and computerequipment. When these pollutants are released intothe air, they come back down with precipitation. Inthis way, and from water washing over contaminatedlandfills, heavy metals get into the water supply.Once in the water, they build up in the food chain.Fish near the top of the aquatic food chain oftencontain high amounts of heavy metals. Therefore,Health Canada and the government of Ontario haveset guidelines about how much of different types offish people should eat to avoid heavy metalpoisoning. Pregnant women in particular arecautioned not to eat too much of certain types offish, as heavy metals can harm the fetus.
It is not always clear how much humans areaffected by heavy metals in their food. However,scientists have seen an effect on contaminatedorganisms. Fish stop functioning normally. Theyseem to be unaware of their natural predators and do not use their ingrained escape-and-evadetechniques. Heavy metal contamination also seemsto affect their sense of smell. Some fish have troublerecognizing their own offspring, and instead ofprotecting them, they eat them. This behaviour couldhave a serious impact on the numbers of some typesof fish in the future — as well as the other organismsin their environment.
Your task is to work with a partner find out whomay be at risk from heavy metals and why. Determinewhat, if anything, the government should do toprotect people from this risk. Use a graphic organizerto keep track of information. After you complete yourresearch, you will present your findings in a poster, aninterview, or another form of media.
Analyze and Evaluate
1. ScienceSource Gather information to help youanswer the questions below and complete youroverall task.
2. Why might Aboriginal peoples and people inremote communities feel the effects of heavymetal contamination of fish more than mostgroups in Canada?
3. (a) What other cultures rely heavily on fish intheir diet?
(b) Should people from these cultures also haveconcerns about heavy metal poisoning?Explain.
4. What can be done to protect people from heavymetal poisoning from their food?
5. Suppose you go fishing at a pond contaminatedwith mercury and catch a minnow (a fish at thebottom of the food chain) and a large trout (afish at the top of the food chain, which eats otherfish). Which fish would have a higherconcentration of mercury in its body? Why?
6. Create an informational poster, a question-and-answer interview that you and your partner canshare with the class, or another form of media,giving the three best ways to protect people fromheavy metal poisoning.
Skill Practice
7. In your research, did a certain type of graphicorganizer seem more helpful than another? Why?
SKILLS YOU WILL USE� Evaluating reliability of data and
information� Using appropriate formats to
communicate results
STSEB18 Skills References 4, 7Decision-Making Analysis
Heavy Metals in Fish
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202 UNIT B Atoms, Elements, and Compounds
B19 Inquiry Activity
Scientists use models to explain things we cannot seeor to display patterns in data.
QuestionHow can a model represent the patterns in the periodic table?
ProcedurePart 1 — Classifying Items Individually
1. Examine the 24 nuts and bolts from the bagprovided by your teacher.
2. Your bag originally contained 25 nuts and bolts,but your teacher removed one of them. Identifywhether a nut or a bolt was removed, anddescribe the missing piece in as much detail aspossible.
3. Share your classification ideas for the missingobject with another group. How were your ideassimilar? How were they different?
4. Revise your classification or description based onyour discussion.
5. Collect the missing nut or bolt from your teacher.How close was your description to the missingobject? Revise your classification or descriptionbased on this new information.
Part 2 — Classifying Items Collectively
6. On a large sheet of paper, make a grid with fiveequal-size columns and five equal-size rows.Make sure the boxes are large enough to hold thelargest nut or bolt. Number the boxes 1 to 25,starting on the top left at number 1 and workingacross the row from left to right. The first box inthe second row should be number 6.
7. Place the smallest bolt at number 1 and thelargest nut at number 25, as shown below inFigures 5.48 and 5.49. Now organize the rest ofthe nuts and bolts on the grid.
8. Follow your teacher’s instructions to measureeither the length and width or mass of each nutand bolt. Record the measurements on your grid.
Building a Periodic Table
SKILLS YOU WILL USE� Gathering, organizing, and
recording relevant data frominquiries
� Interpreting data/information toidentify patterns or relationships
• 24 assorted nuts and bolts in a bag
• extra nut or bolt
• large sheets of paper
• ruler
• balance
• element cards
• graph paper
Materials & Equipment
Skills References 2, 8, 9
1smallestbolt
2 3 4 5
6 7 8 9 10
11 12 13 14 15
16 17 18 19 20
21 22 23 24 25largestnut
Figure 5.48 Grid for organizing nuts and bolts
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203The periodic table organizes elements by patterns in properties and atomic structure.
B19 Inquiry Activity (continued)
Part 3 — Classifying Elements
9. Collect an element card from your teacher.
10. Compare the properties on your card to those ofyour classmates. Find classmates with cards thathave similar element properties. You will form agroup with these students.
11. Make a list of the properties your group’selements all share. Share the list with yourteacher or class. Once your teacher confirmsyour list, you will be given a group number.
12. Arrange all of your group’s element cards in orderof atomic mass.
13. Make another five-by-five grid, as you did in step 6. Complete it, using the order of theelements in the class. Include the atomic massfor each element in your grid. Write the element’sgroup number at the top of the grid.
Analyzing and Interpreting
14. Use your data from Part 2 to graph a nut or boltnumber versus nut or bolt size (length, width, ormass). (The number of each nut or bolt is thenumber of the box in the grid where the nut orbolt was placed.)
15. Record any patterns you notice in this graph.
16. Use your data on the elements from Part 3 tomake a graph of atomic mass versus atomic number.
17. Record any patterns you notice in this graph.
18. Compare the two graphs you made. Whatsimilarities do you see?
19. Examine the periodic table on page 191.Compare your arrangement of elements with thearrangement of elements in the periodic table.Describe their similarities and their differences.
Skill Practice
20. How many electrons do the following elementshave?
(a) carbon
(b) chlorine
(c) magnesium
(d) neon
Forming Conclusions
21. Return to the guiding question for this inquiryactivity. Examine the periodic table on page 191.Based on your data and experiences, answer thequestion.
Figure 5.49 Arranging the nuts and bolts Figure 5.50 The element cards
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204 UNIT B Atoms, Elements, and Compounds
Key Concept Review1. Refer to a periodic table to answer the
following questions.
(a) What is the chemical symbol forsodium?
(b) What element has the symbol Hg?
(c) What element sits directly below carbonin the periodic table?
(d) Which element has atoms with a greatermass: lithium or potassium?
2. Name four properties that DmitriMendeleev used as criteria for organizingthe elements.
3. Name two groups on the periodic table thatinclude elements that conduct heat andelectricity.
4. What is the special name for Group 17 onthe periodic table?
5. Using hydrogen as an example, explain thedifference between atomic number andatomic mass.
6. What happens to an atom if it loses avalence electron?
7. Which of the following atoms typicallyform negative ions?
(a) F (b) Li (c) Ne (d) S (e) Al (f) Be
Connect Your Understanding8. If something occurs periodically — every
Monday, for instance — it can be said tooccur in a pattern. How do you think theperiodic table got its name?
9. How do chemical symbols help scientistsfrom different countries communicate?Why is this important?
10. Use the Bohr diagram below to answer thequestions that follow.
(a) What element is shown?
(b) How many electrons does this atom have?
(c) How many protons does this atom have?
(d) What group in the periodic table doesthis element belong to?
11. In one of Dmitri Mendeleev’s first periodictables, he left two question marks betweenzinc and arsenic.
(a) Why did he predict that eventuallysomeone would discover elements to fitin the spaces he left in his periodic table?
(b) What were these two missing elementsnamed when they were later discovered?
12. Suppose a sample of a metal has a lowmelting point and reacts easily with water.What group does the element belong to?
13. Would the latest elements to be discoveredhave heavier atoms or lighter atoms thanthe other elements? Explain.
Reflection14. How has your understanding of the term
“metals” changed since completing thissection? Write a definition for “metal,” andlist examples of metals with differentproperties.
15. List three ways that you can use the periodictable in your studies that you did not knowabout before completing this section.
For more questions, go to ScienceSource.
5.3 CHECK and REFLECT
Question 10
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Diamonds:Responsible Mining and Production
SCIENCEeverywhereeverywhere
This raw diamond must be processed before it can be used.Diamond mining and processing raise some important ethical,economical, and political issues. Diamond-processing facilitiesproduce waste heat and substances that can harm the environment.Mines, too, have an environmental impact. Mines can interrupt thepath of migrating animals. Sometimes, lakes will be drained in orderto reach underwater diamond deposits. Aboriginal communities thathunt or fish for food are concerned about the impact of the diamondindustry on the local environment.
205The periodic table organizes elements by patterns in element properties and atomic structure.
Diamonds are valued as gems for their clarity and sparkle andbecause they can be cut into detailed designs, as in the diamondshown here. But diamonds have many other uses than as gems. Thehardest natural substance on Earth, diamond resists wear, chemicalchange, and temperature extremes. Diamond is hard enough to cutmany types of rock and so is often used to make specialized sawblades, drill bits, or grinding wheels. In medical and laboratoryequipment, thin, clear diamond membranes cover the openingswhere laser beams or X-rays pass through.
In the 1990s, geologists working in northernCanada made an exciting discovery — severaldiamond deposits! With the opening of the Ekatidiamond mine, 300 km northeast of Yellowknife,Canada became a diamond-producing nation.Canada soon became the world’s third-largestproducer of gemstone-quality diamonds, behindonly Botswana and Russia. For some remoteAboriginal communities, the diamond mines in theNorthwest Territories and Nunavut have becomean important source of income. Shown here is theDiavik diamond mine of the Northwest Territories.
Diamonds:Responsible Mining and Production
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