I~);:r~1ID";~<'''. '".. ~:.. .,...
. 1:5.',;;~ ",,~~: «~~tt.
.""'::"l'",,;"" '"~
CIIAPTEK
10
~
~~:)':~~__ .
Kinds of Atoms -
<~:>.~~,;,,;.:"t.
From: Holt Physical Science; Ramsey, W., Gabriel, L., McGuirk, J., Phillips, C., and Watenbaugh, F., New York, New York. Holt, Rinehart and Winston. 1982.
4 _. 4
10-1.
Many dty streets glow at night from the light of electric signs. One commonly seen type of sign is made of thin glass tubes filled with a gas. When an electric current is passed through the gas, colored light is given off. The atoms in the glowing gas produce this light. How can atoms change electric energy into light? You can answer this question with the help of a model of an atom. In this lesson, you will see how an atom can change one form of energy into another form. When you finish lesson I, you will be able to:
. .
310
IONIZATION
Describe what happens inside an atom when it absorbs and then releases energy. Explain how an atom can give off energy. Unit 3
The Structure of Matter'
.r
..
, ...
..
(
G .
)
)
10-1. An electron in a shell that is far from the nucleus has more energy than an electron close to the nucleus.
/./
. Distinguish between
an atom and an ion.
o Observe fluorescent light
through a diffraction
grating. rdinarily, electrons can move endlessly around O the nucleus in an atom without gaining or losing
f
energy.What happens if the atom is supplied with energyin some form from outside the atom? An electriccurrent, for example, can add energy to an atom. Theextra energy causes an electron in the atom to movefarther away from the nucleus. What makes this happen? The attractive force between the positive nucleusand the negative electron has to be overcome. Theextra energy does this. It overcomes the attraction betweenthe nucleus and the electron. This allows one ormore electrons to jump into a shell farther from the nucleus.It is usually the outer electrons of an atom thatmake these jumps. Adding energy to an electron, energy absorbed
n n n
energy released
10-2. When an atom absorbs energy (left), an electronjumps to a higher energy level. Later, the electronfalls back to its original position and energy is released. er
IChapter 10
Kinds of Atoms
311
10-3. In a spectrum tube, atoms of an element give off light of a particular color.
Unstable electron An electron that has absorbed energy and moved farther away from the atomic nucleus.
causing it to move away from the nucleus, makesthat electron unstable. An unstable electron will fall back into its original position or another position closerto the nucleus. See Fig. 10-1. This happens because the positive charge on the nucleus always causes electrons to be pulled toward it. When an unstable electron moves back toward the nucleus, its extra energyis released. See Fig. 10-2. This energy is generally given off in the form of light. The energy may also be in the form of other parts of the electromagnetic spectrum, such as infrared or ultraviolet waves. If electricityis passed through a gas inside a glass tube, visible lightis given off. See Fig. 10-3. The light is made up of certain frequencies or colors. If the light is passed througha special instrument, each separate color or frequency can be seen as a single bright line. For example, hydro. gen produces several violet-colored lines and somered lines. This particular arrangement of light frequencies is always produced by glowing hydrogen gas. The atoms of each chemical element produce a different and characteristic kind of light, called the spectrum, for that element. A particular kind of atom always produces the same spectrum when it gives off light. Mercury (Hg)
10-4. The spectrum of mercury. This is an example of a brightline spectrum. 312
I
750
I
700
.
I
650
600
Unit 3
I
550
I
500
The Structure
450
I
~
400
of Matter
SPECTRUM OF THE STAR HD 193182 Showing hydrogen SpeClrel
Type: Typical
lines neor the limit of the Bolmer
series.
n 3490
Shell Sior
-
3850 A 161'
1490
I
I
I I I
......_IIU
I I I
"rili I .,11 j
I
Ii
III
.. r_I'1I'I ."
I
1111
,
I
HI3
~ WI~
I I
I 1[1
1111
II
I I
I 'II
I1II
II
III I! ~..o
H30
'
I II,
I
III
III I I H20
I
-
II I liT t
HI!
II I III its spectrum,
I
II11 II I ill
II I III
HII
SeeFig. 10-4. By observing i
II
JII .. L111I1111III81I .1. J.tJiIIIA..A........."I
id' -'" ~JI111111
'I' 'III 1111 I I I 11,11 III
I
I II . I,
"'
II
10-5. Astronomers can learn about the composition of a star by studying the spectrum of that star. This type of spectrum is called a dark-line
spectrum.
astronomers
cantell what kind of atoms are present in a distant star. SeeFig. 10-5. Other conditions in the star are also revealedby its total spectrum.
: There are several different kinds of spectra. A con;
tinuousspectrum is one containing all the colors of the
I rainbow.A rainbow is the most common example of I
thisspectrum. A bright-line spectrum is seen when the
I
electronsin an atom are excited and moved to higher
I energy levels. Then, as the electrons move back to
theirnormal energies, light that is characteristic of the particularkind of atom is given off. If light of all colors travelsthrough a cool gas, the gas will absorb the colorsthat are characteristic of the electron energy levels inthe atoms of the gas. In this manner, a dark-line spectrumis created. This is the type of spectrum that astronomers study. What happens to an atom that has received a very largeamount of energy? A very large amount of energycan cause some electrons to move far away fromthe nucleus. The energy may be enough to cause thenegative electrons to overcome completely the attractionof the positive nucleus. One or more elec-
may completely escape from the atom. When thathappens,the number of electrons will no longer trons
equalthe number of protons in the atom. Normally, there are the same number of electrons moving aroundthe nucleus as there are protons in the nucleus. 'Thisequal number of positive and negative charges Chapter10
Kinds of Atoms
313
10-6. The famous cyclotron at the University of California produced this beam of accelerated particles in 1939. The cyclotron was dismantled in 1962 because it was obsolete.
Ion An atom or molecule with an electric charge.
314
makes an atom electrically neutral. The charges on the electrons and protons cancel each other. If the atom loses any electrons, it is left with more protons than electrons. An atom with extra protonsis a positively charged ion. An ion is an atom or molecule that has an electric charge. An atom becomes a positive ion by losing one or more of its electrons. It is also possible for an atom to gain electrons instead of losing them. An atom that gains electrons will have more electrons than protons. The excess electrons will give the atom a negative charge. An atom that gains oneor more electrons becomes a negatively charged ion. One way to produce ions is to use a machine that produces a beam of moving electrons. See Fig. 10.6. The beam of electrons bombards a group of atoms. The electrons in the beam collide with electrons in the outer shells of the target atoms. These collisions cause electrons to be knocked away from the atom. Thisloss of electrons changes the neutral atoms into positively charged ions. Ions are also produced in the interiorsof stars. The high temperatures that exist there provide enough energy to completely ionize the atoms. Scientists can measure how hard an electron hastoI strike an atom in order to change it into an ion..Then they can determine how much energy is needed to remove an electron from the outer shell of an atom. Unit 3
The Structure of Matter
helium
10-7. This graph shows the energy needed to remove an electron from an atom of the first 20 elements.
neon
o I:0 ...
argon
~I 0'1:
~
~~ Q)
.........
co
>03 0'1>0
I
.....
2
4
8
12
14
16
(C2) helium
20
.
atomic number
Theseenergies, ranging from hydrogen (atomic number 1) to calcium (atomic number 20), form a pattern. Thispattern is shown in the graph in Fig. 10-7. The graph shows that the atoms of the elements helium, neon, and argon require the highest energies to remove electrons. Helium, neon, and argon atoms have a tighter hold on their electrons than other atoms. Helium (atomic number 2) has a total of 2 electrons. Neon has 10 electrons and argon has 18 electrons. Is there something special about the number of electrons in an atom? Remember how many electrons fill each shell around thenucleus of an atom? The first electron shell is full with2 electrons. The second shell fills with 8 electrons. Thushelium has all of its electrons in one completely filledshell. Neon, with 10 electrons, has filled the first andsecond shells (2 + 8). Argon, with 18 electrons, hasits first, second, and third shells filled (2 + 8 + 8). SeeFig. 10-8. Atoms that have completely filled electron shells do noteasily lose electrons. The electron arrangement is stable. A stable electron arrangement means that an atomdoes not tend to gain or lose electrons since all its electronshells are completely filled. The elements with stableatoms are gases. These gases are called the noble gases.Experiments have shown that there are a total ofsixnoblegases among all the elements. In addition to helium,neon, and argon, other noble gases are krypton, xenon, and radon. Krypton has 36 electrons, xenon has 54 electrons, and radon has 86 electrons. Withthese numbers of electrons, the electron shells ofkrypton, xenon, and radon are completely filled. Chapter 1 0
Kinds of Atoms
.
.
-. -"" -.
.
8) / -
. -....--.-. -.
neon
.
. .----
.
-.
-----.
.
.
8
. .
argon 10-8. Why are helium, neon, and argon called noble gases? How are they different from the other elements?
Stable electron arrangement
An arrangement in which all of the are filled.
electron shells
Noble gases The six elements whose atoms have completely filled electron
shells.
315
SUMMARY
How can an atom be made to give off light energy? Electric energy must be added to the atom. One or more electrons absorb the energy and jump to new positions. A fraction of a second later, the energy, now in the form of light, is released as the electron falls back toward the nucleus. Electrons can absorb enough energy to escape the atom completely. Changing the number of electrons changes the atom into an electrically charged ion. The noble gases are made up of atoms with a stable electron arrangement.
QUESTIOrIS
Unless otherwise indicated, use complete sentences to write your answers. 1. The following questions refer to what happens when mercury atoms in a fluorescent tube absorb electric energy. a. What do the electrons in the mercury atom do when they absorb electric energy? b. When the electrons of the mercury atoms absorb electric energy, they become c. What do the electrons do when they give up the energy they absorbed? d. The energy that the electrons absorbed is given off as 2. What must happen to make a mercury atom a positiveion? 3. What must happen to make a mercury atom a negativeion? 4. How are astronomers able to learn about the composition of stars by observing their spectra? 5. In your own words describe what is meant by a noble gas and name three such gases.
__'
er
Chapter 1 0
Kinds of Atoms
317
10-2. CHEMICAL ACTIVITY The Hindenburg was a famous German passenger airship. In 1937, while attempting to land in New Jersey after crossing the Atlantic, it exploded and crashed in flames. What could have caused this disaster? The Hindenburg was filled with hydrogen gas that exploded and burned. Modern airships like the Goodyear blimp are filled with helium. In this lesson, you will see why helium is a safer gas than hydrogen. When you finish lesson 2, you wil be able to:
I
. .
o
Relate the chemical activity of an element to the number of electrons in the outer shell of an atom of that element. Explain why certain elements can be grouped together. Classify nine elements into groups on the basisof their characteristics.
n order to stay in the air, an airship must be filled I with a gas that is lighter than air. The airship then hydrogen
C" .8} helium 10-9. Both hydrogen (H) and helium (He) have only one electronshell. What is the difference between H and He? ~
318
floats in the air in the same way that a piece of wood floats in water. Hydrogen gas is lighter than air. But hydrogen is a dangerous gas. It can burn when mixed with oxygen. A much safer gas for airships is helium. Helium is also much lighter than air. Helium does not burn because it does not combine with oxygen. In fact, helium will not take part in any chemical changes. Helium atoms exist separately. They are never part ofa molecule. Why is it that helium does not take part in chemical changes while hydrogen does? Hydrogen and helium are the only two elements that have only a single electron shell. See Fig. 10-9. This shell can hold only two electrons. Helium already Unit 3
The Structure of Matter
has two electrons. Therefore, helium has a completely filled shell. It does not join with other atoms to form molecules. Hydrogen has only one electron. It needs one more electron to fill the shell. Therefore, unlike helium, hydrogen reacts with many other atoms to form molecules. The way an atom reacts with atoms of other elements is called its chemical activity. Hydrogen, which reacts readily with other elements, is chemicallyactive.Helium, which does not react with other elements, is not chemically active. It is inert. All of the noble gases are inert. Is it possible that the two elements hydrogen and helium behave so differently because of the different number of electrons in their outer shells? If this is true, then atoms with the same number of outer electrons should be alike. In the previous lesson, you learned that atoms with a stable number of electrons do not easilyjoin with other atoms. If an atom has 1, 2, or 3 electronslessthan a stable number of electrons, it will tend to add electrons until a stable number is reached. Ifan atom has 1, 2, or 3 electrons more than a stable number of electrons, it will tend to loseelectrons until a stablenumber is reached. For example, think about a lithium atom. The atomic number of lithium is 3. A lithium atom has 3 electrons. There are 2 electrons in thefirst shell and one electron in the second shell. See Fig.10-10. Thus lithium has one more electron than thestable number of two. Lithium will tend to losethat oneelectron to reach the stable number of two. Table 10-1lists five other atoms that can also be expected to loseone electron. This group of atoms is called the alkali (al-kuh-lie) metals. Now think about a fluorine atom. The atomic numberof fluorine is 9. Fluorine also has 2 electrons in its TABLE10-1
The Alkali Metals Atoms that lose one electron easily
s
Lithium Sodium Potassium Rubidium Cesium Francium
:r
Chapter 1 0
Atomic Number 3 11 19 37 55 87
Kinds of Atoms
Chemical activity Describes the way in which an atom reacts with other kinds of atoms. Inert A description of an atom that does not react with other atoms.
lithium 10-10. How does a lithium atom differfrom a helium atom?
Alkali metals A group of elements whose atoms all have one electron more than the stable number.
Stable electron number after los;ng one electron 2 10 18 36 54 86
319
TABLE10-2 The Halogens Atoms that gain one electron easily
\~' 10-11.How
Fluorine Chlorine Bromine Iodine Astatine
fluorine doesa fluorine
atom differfrom a neonatom?
Halogens A group of elements whose atoms all have one electron less than the stable number.
320
Atomic Number 9 17 35 53 85
Stable electron number after gaining one electron 10 18 36 54 86
first shell. As shown in Fig. 10-11, fluorine has 7 elec. trons in its outer shell. Fluorine has one electron less than a stable number of 8 in its outer shell. Fluorine must add one electron to have a stable electron arrangement. Table 10-2 lists four other elements that will gain one electron to become stable. These ele. ments are called the halogens (hal-uh-juns). Ele. ments like the alkali metals and the halogens that loseor gain electrons readily take part in chemical changes. On the other hand, the noble gases have filled elec. tron shells and do not easily gain or lose electrons. The noble gases do not readily take part in chemical changes. Although the noble gases are not found in great quantities on earth, their lack of chemical activity makes them very useful. The most abundant noble gas is argon. Argon makes up about one percent of the air. Part of the gas used to fill ordinary light bulbs is argon. Its presence inside the bulb helps to slow the rate at which the hot wire filament evaporates, causing the inside of the bulb to blacken. Thus the light bulb stays bright as it is used. Neon is used in advertising signs since it gives off a bright red light when a high-voltage electric current is applied. A mixture of neon and other gases will produce different colors. For example, a mixture of neon and helium will give off a yellow color. As you have already seen, helium is used tofill blimps and balloons. It is also used in certain kinds of welding. The helium gas surrounds the hot metal as the weld is made and prevents gases in the air from reacting with the metal. A mixture of helium and oxy. gen is often breathed instead of air by deep-sea divers. The reason for this is that the nitrogen contained in ordinary air can cause harm when taken into the lungs under high pressure. Unit 3
The Structure of Matter
SUMMARY
Airships like the Goodyear blimp are safe because they are filled with helium gas. The atoms of helium are stable. They do not react with different atoms. Atoms that are not stable tend to gain or lose electrons to reach a stable number. Atoms gain or lose electrons by reacting chemically with atoms of other elements. Atoms with the same number of electrons in their outer shells have similar characteristics.
QUESTIONS
Unless otherwise indicated, use complete sentences to write your answers. Usethe following list to answer questions 1-4: atom A: 7 electrons in outer shell atom B: I electron in outer shell atom C: I electron in outer shell atom D: 7 electrons in outer shell atom E: 3 electrons in outer shell atom F: 8 electrons in outer shell 1.Which of the atoms would be chemically active? 2. Which of the atoms would not be chemically active? 3.What other atom would belong to the same chemical group as atom A? 4.What other atom would belong to the same chemical group as atom B? 5.Name three noble gases and state one use for each of them.
Kinds of Atoms
323
10-3. CIIEMICAL FAMILIES
. . .
You probably know people who are all members of the same family and look some. what alike. They share a family resemblance. They share the same name. Sometimes these family members even behave alike. In this lesson, you will learn that atoms also belong to families. The characteristics of an element determine the family to which it belongs. When you finish lesson 3, you will be able to: Describe what is meant by a chemicalfamily. Explain how you can predict the characteristics of an element by using the periodic chart. Predict the characteristics of a missing member of two different chemical families.
have now identified more than 100 S dentists ent kinds of elements. Additional elements maybe differ-
discovered in the future. Do you think scientists can easily keep track of such a large number of elements? How would you organize a list of all the different elements? One way to organize a large number of different things is to put the names in alphabetical order. For example, your teacher probably keeps an alphabetical list of all the students in your class. In the last activity, the cards representing nine different elements were given to you in alphabetical order. You then found a different system for classifying the cards. The nine elements fell into three groups. Each element was placed in a particular group on the basis of its characteristics. Lithium, sodium, and potassium, for example, had similar properties. They were placed in the same group, called the alkali metals. The general name for a group of elements with similar 324
Unit 3
The Structure of Matter
properties is chemical family. The alkali metals, halogens, and noble gases are each examples of a chemicalfamily. During the early 1800's, scientists discovered that different elements can belong to chemical families. They listed the elements in order of their increasing atomic masses. When they did this, the scientists discovered that certain physical and chemical properties were repeated at regular intervals. In other words, elements with similar properties occurred periodically in thelist. This is like the days ofthe week (Sunday, Monday, Tuesday, and so on), which occur periodically throughout a calendar month. In 1872, a Russian chemist, Dmitri Mendeleev (duhmeet-tree men-d'l-ay-uf), tried to arrange the elementsin another way. See Fig. 10-14. He arranged the elements in the order of their increasing atomic masses. Instead of"listing them one after the other, however, he laid them out as you might deal a deck of cardsfor a game of solitaire. Figure 10-15 shows what hedid. Look at the three elements in the first vertical column: lithium, sodium, and potassium. These are the three elements that belong to the chemical family of alkalimetals. The three elements in the last column are flourine, chlorine, and bromine. These elements belongto the chemical family of halogens.
Chemical family A group of elements that are alike in their chemical behavior.
10-14. Dmitri Mendeleev found a better way to arrange the elements in a periodic chart. Using this chart, he was able to predict the properties of elements that had not yet been discovered.
10-15. Mendeleev's arrangement of the elements in order of increasing atomic mass.
e lithium atomic mass 7
er
beryllium atomic mass9
boron atomic mass 11
carbon atomic mass 12
sodium atom ic mass 23
magnesium atomic mass 24
aluminum atomic mass 27
silicon atomic mass 28
potassium atomic mass 39
calcium atomic mass 40
gallium atomic mass 70
germanium atomic mass 73
Chapter 10
Kinds of Atoms
oxygen atomic mass 16
fluorine atomic mass 19
atomic mass31
sulfur atomic mass32
chlorine atomic mass35
arsenic atomic mass75
selenium atomic mass 79
bromine atomic mass80
nitrogen atomic mass 14
phosphorus
325
1- -atomic number H -atomic mass 1.008 3 4 Li Be 6.94 9.01 11 12 Na Mg 23.0 24.3 20 19 21 22 Ca Sc K Ti 39.1 40.1 45.0 47.9 37 38 39 40 Rb y Sr Zr 85.5 87.6 88.9 91.2 55 56 57-71 72 Cs Ba LaHf 132.9 137.3 Lu* 178.5 87 88 89-103 104 Fr Ra AcRf (223) (226) Lrt (261)
* Lanthanides
I
57
I
58
23 V 50.9 41 Nb 92.9 73 Ta 180.9 105 Ha
24 Cr 52.0 42 Mo 95.9 74 W 183.9 106
25 Mn 54.9 43 Tc (97) 75 Re 186.2 107
26 Fe 55.8 44 Ru 101.1 76 Os 190.2 108
27 Co 58.9 45 Rh 102.9 77 Ir 192.2 109
28 Ni 58.7 46 Pd 106.4 78 Pt 195.1 110
29 Cu 63.5 47 Ag 107.9 79 Au 197.0 111
30 Zn 65.4 48 Cd 112.4 80 Hg 200.6 112
5 B 10.8 13 AI 27.0 31 Ga 69.7 49 In 114.8 81 TI 204.4 113
6 C 12.01 14 Si 28.1 32 Ge 72.6 50 Sn 118.7 82 Pb 207.2 114
7 N 14.01 15 P 31.0 33 As 74.9 51 Sb 121.8 83 Bi 209.0 115
8 0 16.00 16 S 32.1 34 Se 79.0 52 Te 127.6 84 Po 209 116
2 He 4.00 10 9 Ne F 19.0 20.12 17 18 CI Ar 35.5 39.9 35 36 Br Kr 79.9 83.8 53 54 I Xe 126.9 131.3 85 86 At Rn (210) (2221 117 1;8
(260) I (263)
I
59
I
60
t Actinides
10-16. The modern periodic chart of the elements. The numbers shown in the colored boxes represent the atomic numbers of elements that have not yet been discovered.
Periodic chart An arrangement of all the elements, showing the chemical families. Write the names of as many of the elements in the periodic chart as you can. See Table 9-4 on p. 301. (Note: Element 104 is known as both kurchatovium, Ku, and rutherfordium, RfJ
326
Mendeleev discovered that when he arranged allthe elements in a table like this, elements in the same chemical family were found in the same vertical column. Elements in each family are found at particular periods or places when you put them in order. Mendeleev's chart is called the periodic chart of the elements. Modern periodic charts are slightly different from Mendeleev's original one. A modern periodic chart has the elements arranged in order of their increasing atomic numbers. This causes only small changes from Mendeleev's original arrangement according to atomic mass. In a modern periodic chart, each kind of atomis found in a separate box. See Fig. 10-16. The symbolfor the element is given in the middle of the box. Above the symbol is the atomic number of the element. Below is the atomic mass. On some periodic charts, the electron arrangement for an atom of each element is also shown in the box.. Other information about the properties of the element may be included within the box. A map would be helpful if you had to find your way around an unfamiliar city. In the same way, a periodic Unit 3
The Structure of Matter J
l
chart is useful in learning about the chemical elements. Each vertical column of the chart lists elements with similar properties. For example, the noble gases are found in a single column at the right side. Next to the noble gases is the column containing the halogens. The alkali metals are found in a single column at the far left of the chart. All the columns between the right and left sides of the chart list elements with some similarities. The two long rows at the bottom contain elements that would all fit in the third column of the chart. They are placed here to avoid making a very long, single column. Hydrogen is usually put alone at the top of the chart since it resembles both the alkali metals and the halogens. Each horizontal row of the chart is called a period. Within each row or period, the properties of the elements generally repeat periodically. Each row begins with an alkali metal element and ends with a noble gas. The elements in the rows between the alkali metals and the noble gases change from metals to nonmetals when moving from left to right across the row. This pattern is repeated periodicallywithin each row. The fourth row contains elementsthat are unlike any in the above rows. This is the reason for the gap in the top rows on the chart. Mendeleev discovered a valuable tool for scientific research. Each element has its own position on a periodicchart. If you know the chemical properties of two orthree elements, you can predict the properties of a neighboring element. You can even predict the chemicalbehavior of elements not yet discovered. Mendeleevhimself predicted the general properties of several elements that had not yet been discovered. In many cases,when the elements were discovered, they were found to behave almost exactly as Mendeleev had predicted.
) ACTIVITY
I
Predicting the
Characteristics of an Element A. Obtain the materials listedinthe margin. Youhave three cards describinglithium, sodium, Chapter 1 0
Kinds of Atoms
and potassium. These three elements belong to the chemical family called the alkali metals.
Materials cards for: lithium, sodium, potassium, helium, neon, argon, rubidium, and krypton
327
QUESTIONS
Unless otherwise indicated, use complete sentences to write your answers. An atom of the element beryllium has two electrons in its outer shell. These two electrons are given up rather easily to form an ion having a +2 charge. Beryllium is a solid. It also behaves as a typical metal. Use this information to answer questions I and 2. 1. From the following descriptions, choose the one element that would belong to the same chemical family as beryllium. a. aluminum: solid, metal, + 3 ion, 3 electrons in outer shell b. tin: solid, metal, +4 ion, 4 electrons in outer
shell
.
c. radium:
solid, metal, +2 ion, 2 electrons in outer shell d. polonium: solid, metal, -2 ion, 6 electrons in outer shell 2. Magnesium belongs to the same chemical family as beryllium. a. How many electrons would an atom of magnesium have in its outer shell? b. List three other probable characteristics of magnesium. 3. The three main items shown on the periodic chart (Fig. 10-16) are a. chemical symbol b. atomic number c. atomic mass. Explain each of these in your own words. 4. What are elements found in the same vertical column of the periodic chart called?
r
Chapter 10
Kinds of Atoms
329
VOCABULARY REVIEW Match the number of the word(s) with the letter of the phrase that best explains it.
1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
inert noble gases chemical activity stable arrangement ion chemical family unstable electron alkali metals halogens periodic chart
a. An atom or molecule that has an electric charge. b. An electron arrangement of completely filled shells. c. An electron that has absorbed energy. d. The way an atom reacts with other atoms. e. Does not react. f. A group of elements with similar chemical behavior. g. The six elements whose atoms have filled electron shells. h. Group of elements having one less electron than the stable number. i. Group of elements having one more electron than the stable number. j. An arrangement of all the elements showing the chemical families.
REVIEW QUESTIONS Complete each statement by filling in the blank.
by choosing the best word or phrase, or
1. When an atom absorbs energy, its a. electrons move to a greater distance from the nucleus b. protons move faster c. electrons move closer to the nucleus d. protons move to a greater distance from the nucleus. 2. When an atom releases energy, its a. electrons move to a greater distance from the nucleus b. protons move faster c. electrons move closer to the nucleus d. protons move to a greater distance from the nucleus. 3. If an atom gains an extra electron, the atom becomes a. a positive ion b. a neutral atom c. a negative ion d. a new element. 4. An atom has a stable electron arrangement if it a. requires a great deal of energy to release an electron b. has completed electron shells c. isa noble gas d. all of these are correct. 332
Unit 3
The Structure of Matter
5. An atom whose electron arrangement is 2, 8, 7 would become stable if it 6. The alkali metals and halogens are chemically active because they a. have the same number of electrons b. have completed electron shells c. easily gain or lose electrons d. do not easily gain or lose electrons. 7. The noble gases are grouped together since they a. have the same number of electrons in their outer shells b. are all gases c. are inert d. all of these are properties the noble gases have in common. 8. Groups of elements that chemically behave the same a. belong to the same chemical family b. have the same number of electrons c. have the same number of protons d. are always inert. 9. The symbols for all the members of the halogen family are 10. The was used by Mendeleev to predict the general properties of several elements not yet discovered at the time.
REVIEWEXERCISES Give complete but brief answers to each of the following. Use complete sentences to write your answers. I. Explain how an atom can absorb and then release energy. 2. Describe what happens when an atom becomes an ion. 3. What happens when electricity is passed through a glass tube containing a gas? 4. What is meant by a noble gas? 5. Give an example of an electron arrangement that is stable. 6. A certain atom has 2 electrons in its first shell, 8 electrons in its second shell, and I electron in its third shell. Will it gain or lose electrons to have a stable arrangement? 7. How is chemical activity related to electron arrangement? 8. Why are some elements, such as the alkali metals, grouped together? 9. Describe what is meant by a chemical family. 10. How can knowing the position of an element in the periodic chart be of value?
er Ive l e er ve he
EXTENSIONS
on l. Use the library to find more complete descriptions of the members of the alkali metal family. How are they similar? different? 2. Look up characteristics of the halogen family. Describe some uses of halogen compounds.
eal sa ter
Chapter 1 0
Kinds of Atoms
333
