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CH4:

Atomic Structure

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Pretest

1. True or False: Compounds have fixed compositions.

2. What is an atom?

3. Which of the following units is a unit of mass?

a. mLb. ˚C c. gd. cm

Chapter 4

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Pretest (continued)

4. Volume is

a. the straight-line distance between two points. b. the quantity of matter in an object. c. the amount of space taken up by an object. d. a representation of an object or event.

5. What is density?

Chapter 4

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Pretest (continued)

6. Which two of the following events can take place when a liquid absorbs energy?

a. The average kinetic energy of the particles in the liquid increases.

b. The temperature decreases. c. The liquid freezes. d. The liquid changes to a gas.

Chapter 4

Pretest Answers

1. True or False: Compounds have fixed compositions.

2. What is an atom?

3. Which of the following units is a unit of mass?

a. mLb. ˚C c. gd. cm

Chapter 4

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An atom is the smallest particle of an element.

Chapter 4Pretest Answers (continued)

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4. Volume is

a. the straight-line distance between two points. b. the quantity of matter in an object. c. the amount of space taken up by an object. d. a representation of an object or event.

5. What is density?

Density is the ratio of the mass of a substance to its volume.

Chapter 4Pretest Answers (continued)

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6. Which two of the following events can take place when a liquid absorbs energy?

a. The average kinetic energy of the particles in the liquid increases.

b. The temperature decreases. c. The liquid freezes. d. The liquid changes to a gas.

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Interest Grabber

Using AnalogiesThe network of blood vessels in your body is like the network of streets and highways in a large city. How are the two networks similar? Both networks are used to transport objects from one location to another. The comparison is an example of an analogy. An analogy uses a similarity to compare two objects or systems. A familiar object is often used to help explain a less familiar object.

1. Atoms in compounds are like bricks in a wall. Explain this analogy.

2. Think of another analogy for atoms in compounds.

Section 4.1

Interest GrabberAnswers

1. Atoms in compounds are like bricks in a wall. Explain this analogy.

You may say that atoms and bricks are both small units from which larger structures are built.

2. Think of another analogy for atoms in compounds.

Answers will vary. Possible analogies include corals in a reef, threads in a woven rug, seats in a stadium, or blades of grass in a lawn.

Section 4.1

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4.1 Studying Atoms

A.Ancient Greek Models of Atoms

1.Democritus-particles could not be divided

2.Aristotle believed matter could be divided indefinitely

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4.1

B. Dalton’s Atomic Theory

1. “Matter is made up of individual particles that cannot be divided”

a. All elements are made of atoms

b. Atoms of the same elements have the same mass, different atoms have different masses

c. Compounds contain atoms of more than one element

d. Compounds always form in fixed composition (ratios)

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4.1

C. Thomson’s Model of the Atom

1. Experiments showed atoms are made of smaller subatomic particles

2. Model:

a. An atom is neutral

b. Negative particles are evenly distributed throughout a positively charged mass of matter

c. Aka “plum pudding” model

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Thomson’s Experiments Figure 5

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4.1

D.Rutherford’s Model:

1. Used gold foil experiment to discover that atoms have a nuclei

a. Nucleus= dense, positively charged mass located in the center of the atom

b. Showed that positive particles are concentrated and NOT evenly distributed

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The Gold Foil Experiment

Figure 5

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Reading Strategy

Summarizing

Section 4.1

a. Dalton b. Indivisible, solid spheres

c. Thomson d. Negative charges evenly scattered through a positively charged mass of matter

(plum pudding model)

e. Deflection of alpha particles passing through gold foil

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Interest Grabber

The “Rutherford” Atom

In Section 4.1 you were told that if the Houston Astrodome were a model for an atom, then a marble could represent its nucleus.

1. Think of another physical analogy for a “Rutherford” atom other than the Astrodome.

2. Identify what represents the atom and what represents the nucleus in your analogy.

3. How good a match is your analogy for an actual atom? In what ways is it misleading?

Section 4.2

Interest GrabberAnswers

1. Think of another physical analogy for a “Rutherford” atom other than the Astrodome.

2. Identify what represents the atom and what represents the nucleus in your analogy.

1. and 2. Sample answers: a fruit with a seed representing the nucleus; a small object embedded in the center of a transparent glass or plastic sphere; a chocolate-covered cherry or nut; the smallest object in a set of nested objects of increasing size

3. How good a match is your analogy for an actual atom? In what ways is it misleading?

The main flaws in most physical analogies are the relative sizes of the “nucleus” and “atom,” and the lack of unfilled space surrounding the nucleus.

Section 4.2

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4.2 The Structure of the Atom

A. Properties of Subatomic Particles:

1. Proton=positive, subatomic particle, found in nucleus

a. 1+ charge

b. All atoms have at least 1

2. Electron=negative, subatomic particle, found outside nucleus

a. 1- charge

3. Neutrons=neutral, subatomic particle, found in the nucleus

a. Same mass (approximately) as a proton

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4.2

B. Atomic Number and Mass Number

1. Atomic number=the number of protons in 1 atom of an element

a. Hydrogen – only atom to have 1

b. Always balanced with equal number of electrons so atomic number = electron number

2. Mass number= sum of the protons and neutrons in the nucleus of an atom

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A Scientific Method Figure 12

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4.2

C.Isotopes= atoms of the same element that have different number of neutrons and therefore different atomic masses

1. Oxygen-16, oxygen-17, oxygen-18

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Reading Strategy

Monitoring Your Understanding

Section 4.2

Most students will know that atoms are the "building blocks" of matter, and some may know that atoms contain subatomic particles. Based on the title of the section, students may say that they want to learn more about the structure of atoms.

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Interest Grabber

ProbabilityScientists use probability to describe how electrons behave in atoms. Try the following activity to learn more about probability.

Tape a large piece of paper to the wall. Draw a circle 1-foot in diameter in the center of the paper. Mark the exact center of the circle. Leave plenty of room on all sides of the circle. Blindfold a partner. Place your partner two arm lengths away from the wall facing the wall. Give your partner a small sticker. Have your partner walk forward and try to place the sticker at the center of the circle. Repeat this process five times.

1. Describe the pattern of the stickers.

2. Was the probability of placing a sticker in the center of the circle high or low?

3. What could increase the probability of placinga sticker inside the circle?

Section 4.3

Interest GrabberAnswers

Section 4.3

1. Describe the pattern of the stickers.

Sample responses: Three stickers were placed inside the circle, one sticker was placed on the center dot.

2. Was the probability of placing a sticker in the center of the circle high or low?

Sample response: The probability of placing the sticker in the center was low.

3. What could increase the probability of placing a sticker inside the circle?

A larger circle would increase the probability. So would starting the blindfolded person from a location nearer to the wall.

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4.3 Modern Atomic Theory

A. Bohr’s Model of the Atom

1. Danish physicist

2. Model focused on electrons

a. Electrons move with fixed speed around nucleus in orbits

b. Energy levels=possible energies an electron can have (determines location outside nucleus)

i. Electrons gain and lose energy… this causes change in energy level

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4.3

B.Electron Cloud Model:

1. Alters Bohr’s model from electrons in fixed orbits to more random movements

2. Electron cloud=visual model of probable locations of electrons

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4.3

C. Atomic Orbitals

1. Orbitals= region of space around the nucleus where an electron is likely to be located

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4.3

D.Electron Configuration= arangements of electrons in the orbitals of an atom

1. Ground state=when all electrons in the atom have the lowest possible energies

2. More stable than when in “excited state”

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Reading Strategy

a. Electron moves to higher energy level.

b. Electron moves to lower energy level.

Section 4.3

Sequencing

Chapter 4Go Online

Self-grading assessment

For links on atomic theory, go to www.SciLinks.org and enter the Web Code as follows: ccn-1041.

For links on subatomic particles, go to www.SciLinks.org and enter the Web Code as follows: ccn-1042.

For links on energy levels, go to www.SciLinks.org and enter the Web Code as follows: ccn-1043.