CHAPTER 2

Atoms: The Building Blocks of Matter

Section 1   Section 2   Section 3  

Section 4  Section 5  Section 6  Section 7  

Section 8   Section 9   Section 10

Section 11  Section 12  Section 14

SECTION 2.1 What is Matter?

1.  Matter is defined as anything that has mass and occupies space.

a)  Anything that has mass and occupies ________ is said to be matter.

b)  The amount of ________ an object occupies is known as its volume.

2.  An actual measurement of the amount of matter contained in an object is known as the mass.

Mass is a measurement of the amount of ________ in an object.

3.  An object’s weight is a measurement of gravitational force pulling on that object.

a) ________ is a measure of gravitational force acting on an object.

b) Jupiter has a stronger gravitational force than Earth.  On Jupiter, an object would have (more, less, the same) weight as on Earth, and the mass would be (more, less, the same) as on Earth.

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SECTION 2.2  Atoms

4. An atom is the smallest particle of matter that cannot be chemically broken down into smaller constituents.  Pure substances that contain only one kind of atom are called elements.

A block of the element lead has only ________ atoms in it.

5.  The elemental symbol is based on the element’s name and is made up of a single capital letter or a capital letter followed by a lowercase letter.

Give the symbols for the following elements (see Table 2.1).

a)     lithium

b)    helium

c)     sodium

d)  potassium

e) sulfur

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Section 2.3 The Structure of Atoms

6.  According to current theories, there are three key particles contained within atoms.  They are protons, neutrons and electrons and are known as subatomic particles.

The fundamental subatomic particles are:  protons, electrons and ________.

7.  Some characteristics of these subatomic particles, such as their mass, electrical charge and location within the atom, help to explain the behavior of matter (see Table 2.2 and Figure 2.1).

Three characteristics of subatomic particles that help explain the behavior of matter are the location within the atom, mass and ________ charge.

8.  Protons, along with neutrons, make up the central portion of an atom known as the nucleus.  Protons each have a charge of +1.

Where are protons located within the atom?

9.  Because protons each have a +1 charge and neutrons have no charge, the nucleus of an atom has a positive charge that is equal to the number of protons it contains.

A nucleus contains four protons.  What is its charge?

10.  Electrons are located outside the nucleus and carry a –1 charge.  In a neutral atom, the number of electrons is the same as the number of protons, giving the overall atom no electrical charge.

The electrical charge of an electron is ________.  In an electrically neutral atom with 4 protons there would be ________ electrons.

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SECTION 2.4 Isotopes

11.  The atomic number of an atom refers to the number of protons within the nucleus of that atom.  Therefore, all atoms of a specific element have the same atomic number.  The atomic number is symbolized as “Z” and is the smaller number contained in an element’s box on the periodic table (see the Periodic Table inside the text cover).

Which element has 26 as its atomic number?

12.  The number of protons plus the number of neutrons within an atom make up its mass number and is represented by the symbol A (see Example 2.1). 

The element copper (Cu) has an atomic number of 29 and a mass number of 64.  How many neutrons does one atom of Cu contain?

13.  Isotopes are atoms that have the same atomic number but different mass numbers.

According to the statement above, atoms that are isotopes must have the same number of protons but different numbers of ________.

14.  The following notation is used to identify isotopes: .  Where E is the symbol for the element, A is the mass number, and Z is the atomic number.

Determine the number of protons, number of neutrons and the number of electrons in atoms of the following isotopes.  Remember, the number of electrons equals the number of protons in electrically neutral atoms.

a)    

b)   

c)    

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SECTION 2.5 Relative Atomic Masses

15.  The atomic mass unit (u) is used to express the relative mass of atoms.  One u is equal to 1/12 the mass of an atom of .

1/12 the mass of a atom is equal to the mass of one ________.

16.  The relative masses of atoms are expressed in atomic mass units (u).  They appear with the elements on the periodic table and are more commonly referred to as atomic weights.  The atomic weight is the larger of the two numbers appearing with an element in the periodic table.

The atomic weights of elements are expressed as ________ on the periodic table.

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Section 2.6 The Electronic Structure of Atoms

17.  Shells are the energy levels that electrons occupy as they orbit the nucleus (see Figure 2.3).

Electrons orbit the nucleus in ________.

18.  a) Following Example 2.3 and using Figure 2.2, determine the number of electrons in each shell for an atom of aluminum (Al).

b)  How many total electrons can be held in

1) the first shell

2) the second shell

3) the third shell

19. In atoms, the outermost shell that contains electrons is known as the valence shell.  The electrons in this shell are called valence electrons and are responsible for the chemical properties of the atom.

Chemical properties of atoms are due to the ________  ________ found in the _________ ________ of the atom.

20. Following Example 2.4 and using Figure 2.2, determine the number of valence electrons in an atom of boron (B).

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Section 2.7 The Periodic Law and Table

21.  The periodic table or the periodic table of elements is the chart commonly seen in chemistry books that contains all the known elements and information about them (see inside front cover).

All of the known elements are organized on the ________ table.

22.  The elements are arranged in a specific order on the periodic table.  This order stems from the periodic law, which says that when elements are arranged in order of increasing atomic number, elements with similar characteristics occur at regular intervals.

According to the ________  ________, when elements are arranged in order of increasing atomic number, elements with similar properties occur at regular intervals.

23.  The vertical columns on the periodic table are known as groups or families.  Elements contained within the same group or column share similar chemical properties.

Vertical columns on the periodic table are referred to as families or _______.

24.  On the periodic table of elements, the horizontal rows are referred to as periods.  Periods are numbered from top to bottom.

The ________ rows on the period table are called periods.

25.  Each element belongs to both a period (horizontal row) and a group (vertical column) of the periodic table.

What element is found in period 5, group IIIA on the periodic table?

26.  Using Figures 2.5 and 2.6 determine the number of protons and electrons for each of the following and state whether they are a representative element, noble gas, transition element, or an inner transition element.

a) period 5, group VI B

b) period 2, group I A

c) uranium (U)

d) xenon (Xe)

27.  The elements of the periodic table can also be divided according to their classification as metals, metalloids or nonmetals.  Metals comprise the majority of elements and are located on the left two-thirds of the periodic table.  Metals are characteristically good conductors of heat and electricity, very malleable and ductile, as well as having a metallic luster (see Figure 2.7).

Comprising two thirds of the periodic table, _______ make up a majority of the elements.

28.  The right one third of the periodic table is where the nonmetal elements can be located.  These elements have characteristics opposite to those of metals and are often brittle, powdery solids or gases. 

A non-metal is a ________ conductor of electricity.

29.  The metalloids on the periodic table separate the metals from the nonmetals by creating a diagonal boundary.  Metalloids can demonstrate properties intermediate between those of metals and nonmetals.

A number of elements at the interface of metals and non-metals are classified as ________.

30.  Using the information in numbers 27-29 above and Figure 2.7, answer the following questions:

a)  Will the element at period 4, group VII B conduct electricity?

b) Will the element with 16 protons be brittle or malleable?

c) Will the element with 14 electrons conduct electricity?  Will it be brittle or malleable?

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Section 2.8 The Electronic Structure of Representative Elements

31.  When trying to figure out the number of electrons in the valence or outermost shell, there is another strategy for making things easier.  The number of electrons in the valence shell is equal to the Roman numeral of the family or group (the vertical column) in which the element is located (see periodic table inside front cover and Example 2.7).

Indicate how many electrons are in the valence shell of the following elements:

a)     P

b)    calcium

c)     Cl

d) arsenic

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Section 2.9 Radioactive Nuclei

32.  Nuclei that undergo spontaneous changes and emit energy in the form of radiation are known as radioactive nuclei.

Radioactive nuclei are nuclei that emit _______.

33.  Radioactive decay is a process in which an unstable nucleus changes energy states and emits radiation.

A nucleus that is changing energy states and emitting radiation is experiencing ________ ________.

34.  Alpha particles are the most massive particles emitted by radioactive nuclei.  They are the particles that make up alpha rays, and their composition is identical to the helium nucleus: two protons and two neutrons (see Table 2.4).  Most alpha particles cannot penetrate more than a sheet of paper.

The charge of a single alpha particle is ________.

35.  Beta particles are identical to electrons but are produced in the nucleus.  Evidence suggests that an unstable neutron splits into a proton and an electron, ejecting the electron from the nucleus as a beta particle (see Table 2.4).  Most beta particles cannot penetrate more than a wood board.

________ particles carry a charge of –1. 

36.  Excess energy emitted from the nucleus in the form of high energy electromagnetic radiation is known as gamma rays, which carry no charge (see Table 2.4).  Gamma rays can pass directly through many materials.

a)  Though ________ rays have no charge, they can be dangerous to living organisms because they are electromagnetic rays with even more energy than X-rays.

b)  Designate each of the following as an alpha particle, beta particle, or gamma ray.

1) Has no electrical charge or mass

2) Is basically the same as an electron

3) Is given the symbol ⁰_-1e

4)  Is made up of 2 protons and 2 neutrons

5) Is very damaging because of its high energy

6) Is given the symbol ⁴₂He

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Section 2.10 Equations for Nuclear Reactions

41.  For some unstable nuclei, electron capture is their mode of radioactive decay.  In this process, an electron from outside the nucleus is drawn into the nucleus where it combines with a proton to form a neutron (see Example 2.10).   Fill in the blanks with appropriate numbers or symbols (e = beta, positron; He = alpha) for the following.  Their mode of decay is indicated in parentheses.

1)         2)      3)  136C (beta emission) 4) 23592U (alpha emission) 5) 21083Bi undergoes alpha emission. 6) 10850Sn undergoes electron capture.

Check Answers   SECTION 2.11 Isotope Half-Life   42.  The rate of radioactive decay is measured in something we call half-lives.  A half-life is defined as the time required for one-half of the unstable nuclei in a sample to undergo radioactive decay (see Example 2.11).   A)  Mercury-196 has a half-life of 65 hours.  This isotope is used to make diagnostic kidney scans.  A patient is given a 5.0ng dose.  How many nanograms will be present in the patient 260 hours later?   1)  First, calculate how many 65 hr half-lives are in 260 hours.  There are (give number) half-lives. 2)  Next, take the original 5.0 ng of Hg-196 dose and divide it by 2.  Repeat this process once for each half-life that has elapsed.  After 260 hours there will be (give 2 significant figures) ________ ng of Hg-196 remaining. b)  A sample of radioactive Cs-125 has a mass of 0.5000 g.  After undergoing radioactive decay for 2.25 hours, only 0.0625 g remained.  What is the half-life for Cs-125? 1) First calculate how many half-lives have occurred by continuously dividing the original mass by 2: 0.5000 g → 0.2500g → 0.125 g → 0.0625 g A total of ________ half-lives has occurred. 2) Next, divide the total time that has elapsed by the number of half-lives to get the time/half-life.  For Cs-125, this would be ________.  Check Answers SECTION 2.12 The Health Effects of Radiation   43.  Radiation can be very dangerous to living organisms.  Radiation carries such high energy that it has the ability to knock electrons right out of atoms that it strikes.  When this happens, free radicals, or electron deficient particles are created.  Free radicals are very reactive.   a)  As high-energy, ionizing radiation passes through the tissues of living organisms; highly reactive ________  ________ may be formed which can react with stable cellular material resulting in mutations, cancer, etc. b)  If a potassium atom had an electron knocked out of its orbit by ionizing radiation it would become a ________ ________.   44.  When exposed to intense short term radiation, a variety of symptoms, known as radiation sickness, may follow (see Table 2.7).   Intense radiation can rapidly destroy tissue making it a great tool to treat some cancers.  However, ________  ________ is the down-side to this use of short-term intense radiation.  Check Answers SECTION 2.14 Medical Uses for Radioisotopes 45.  Radioactive isotopes can be used medically in diagnostic applications.  Because the location of radioisotopes in the body can be readily detected, their progress through the body and localization in specific organs can be followed or traced.  Radioisotopes used in such medically diagnostic applications are referred to as tracers.   A specific amount of iodine-123 is introduced into the body.  Later, a large amount is detected in the thyroid gland suggesting an overactive thyroid.  In this situation, iodine-123 was used as a(n) ________.

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