Download Chapter 04 - NPHSPhysicalScience

CH4:
Atomic Structure
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Pretest
Chapter 4
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.
b.
c.
d.
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mL
˚C
g
cm
Pretest (continued)
Chapter 4
4. Volume is
a.
b.
c.
d.
the straight-line distance between two points.
the quantity of matter in an object.
the amount of space taken up by an object.
a representation of an object or event.
5. What is density?
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Pretest (continued)
Chapter 4
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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Pretest Answers
Chapter 4
1. True or False: Compounds have fixed compositions.
2. What is an atom?
An atom is the smallest particle of an element.
3. Which of the following units is a unit of mass?
a.
b.
c.
d.
mL
˚C
g
cm
Click the mouse button to display the answers.
Pretest Answers
Chapter 4
(continued)
4. Volume is
a.
b.
c.
d.
the straight-line distance between two points.
the quantity of matter in an object.
the amount of space taken up by an object.
a representation of an object or event.
5. What is density?
Density is the ratio of the mass of a substance to its volume.
Click the mouse button to display the answers.
Pretest Answers
Chapter 4
(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.
Click the mouse button to display the answers.
Interest Grabber
Section 4.1
Using Analogies
The 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.
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Interest Grabber
Section 4.1
Answers
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.
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
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Figure 5
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
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Figure 5
Reading Strategy
Section 4.1
Summarizing
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
Section 4.2
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?
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Interest Grabber
Section 4.2
Answers
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.
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
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Figure 12
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
Section 4.2
Monitoring Your Understanding
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
Section 4.3
Probability
Scientists 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 placing
a sticker inside the circle?
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Interest Grabber
Section 4.3
Answers
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.
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
Section 4.3
Sequencing
a. Electron moves to higher energy level.
b. Electron moves to lower energy level.
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Go Online
Chapter 4
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.