Download Chapter #4 Section Assessment #1 - 33

Chapter #4 Section Assessment
#1 - 33
4.1 Section Assessment
1. How did Democritus characterize atoms?
Democritus believed that atoms were indivisible (you
couldn’t split them into pieces, hence the name
“atomos”), and they were indestructible.
Do we still believe these things to be true?
No. Atoms can be split.
J. J. Thomson discovered the electron in c. 1897.
The “atom bomb” gets its explosive power from splitting
uranium or plutonium atoms in half.
Democritus
460 B.C. – 370 B.C.
4.1 Section Assessment
1. How did Democritus characterize atoms?
Democritus believed that atoms were indivisible (you
couldn’t split them into pieces, hence the name
“atomos”), and they were indestructible.
Do we still believe these things to be true?
No. Atoms can be destroyed.
Antimatter, discovered in 1932 by Carl D. Anderson,
destroys matter when it touches it.
Matter and antimatter explode with a hundred times
more force than nuclear bombs as they annihilate each
other.
Democritus
460 B.C. – 370 B.C.
4.1 Section Assessment
2. How did Dalton advance the atomic philosophy proposed by Democritus?
Dalton used experimental methods, whereas Democritus had used only imagination and
reasoning.
Dalton also had much better knowledge of the elements, and he studied the mass ratios in
which elements combined to make compounds.
Democritus
460 B.C. – 370 B.C.
Ancient Greek
“elements”
fire
Modern
“States of
Matter”
Some of Dalton’s
elements
hot gas or plasma
air
gas
water
liquid
earth
solid
hydrogen oxygen
nitrogen carbon
sulfur
phosphorus
John Dalton
1766-1844
4.1 Section Assessment
3. What instrument can be used to observe individual atoms?
The scanning tunneling microscope can generate pictures where individual atoms can be
distinguished.
For instance, on page . . 103,
.
each iron atom in the picture appears as a single . . .
cone.
Scanning Tunneling Microscope
1981
4.1 Section Assessment
4. In your own words, state the main ideas of Dalton’s atomic theory.
i) All matter is composed of tiny, indivisible particles called “atoms”.
Is everything he said here still believed to be true?
ii) Atoms of the same element are identical. The atoms of any one element are different from
those of another element.
Is everything he said here still believed to be true?
iii) Atoms of different elements can physically mix together or can chemically combine in simple
whole-number ratios to form compounds.
Is everything he said here still believed to be true?
iv) Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one
element, however, are never changed into atoms of another element as a result of chemical
reaction.
Is everything he said here still believed to be true?
4.1 Section Assessment
5. According to Dalton’s theory, is it possible to convert atoms of one element into atoms of
another? Explain.
According to Dalton, atoms can not be changed from one element to another. For example, a
carbon atom will always be a carbon atom, forever.
Of course, we know better than that now. We now know that in addition to chemical reactions,
which merely rearrange atoms, there are also nuclear reactions, which DO change atoms from
one element to another.
For instance, carbon-14 atoms will spontaneously turn into nitrogen-14 atoms by the process of
radioactive decay.
Does that mean that Dalton was an idiot?
NO WAY! Dalton was brilliant.
Even Einstein was wrong about certain things.
4.1 Section Assessment
6. Describe the range of radii of most atoms in nanometers (nm).
5 x 10-2 nm to 2 x 10-1 nm
That’s the short version of the answer.
If you know how to get that answer, then click the red button below to skip to #7.
You can also click the red button if you just don’t care about #6.
If you don’t understand how to get the answer to #6 and you do want to learn how, then click
the green button instead.
Skip to #7
I want to learn about #6!
Okay. Buckle your seatbelt.
4.1 Section Assessment
6. Describe the range of radii of most atoms in nanometers (nm).
The book says, on page 103, at the beginning of the 3rd paragraph, that “The radii of most atoms
fall within the range of 5 x 10-11 m to 2 x 10-10 m.”
First of all, we’d better make sure we know what “radii” means.
The width of a circle is called its “diameter”.
Half the width of a circle is called its “radius”.
The radius is the distance from the center of the
circle to the edge of the circle.
“Radii” is just the plural of “radius”.
A yardstick is three feet long.
An American football field is 100 yards long.
These days, America is the only
country that measures distance in
yards.
The rest of the world uses the metric
system.
In the metric system, the meter is
used instead of the yard.
A meter is a little bit longer than a
yard.
An ordinary ruler is twelve inches long.
0
1
INCHES
2
5
4
3
7
6
8
9
10
11
12
cm
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
. . . You will notice that it is about 30 centimeters long.
A paperclip is about
one centimeter
wide.
0
If you flip it around . . .
If you look closely, you will notice that there are ten tiny marks between each centimeter.
These marks are one millimeter apart.
If you look closely, you will notice that there are ten tiny marks between each centimeter.
These marks are one millimeter apart.
The wire that a paperclip is made out of is about one millimeter thick.
A millimeter is pretty small, isn’t it?
A one-millimeter metal wire is still much thicker than a
human hair, though.
According to the tables on page 74, how big is a nanometer?
It says that 1 m = 109 nm
109 is 1,000,000,000, which is one billion.
Therefore, a nanometer is one one-billionth of a meter.
The tables also say that 1 m = 103 mm
103 is 1,000, which is one thousand.
Therefore, a millimeter is one one-thousandth of a meter.
If 1m = 109 nm and 1 m = 103 mm, then . . .
109 nm = 103 mm
103
103
10(9-3) nm = 1 mm
1 mm = 1,000,000 nm
A nanometer is one one-millionth of a millimeter.
That’s small.
106 nm = 1 mm
If you got confused during the math on that
last slide, don’t worry.
I was just tyring to show you how
ridiculously small a nanometer (nm) is.
What metric unit of length is just a bit longer
than three feet?
1 meter = 1 m
How wide is a paper clip?
1 centimeter = 1 cm
How thick is the wire that a paper clip is made
of?
1 millimeter = 1 mm
1 nm = one one-billionth of a meter
How big is a nanometer?
1 nm = one one-millionth of a
millimeter
GREAT!
Now that you know your
units, let’s do the math . . .
4.1 Section Assessment
6. Describe the range of radii of most atoms in nanometers (nm).
The book says, on page 103, at the beginning of the 3rd paragraph, that “The radii of most atoms
fall within the range of 5 x 10-11 m to 2 x 10-10 m.”
Unfortunately, we need to give our answer in nm, not m.
Page 103 gives us good information, but it’s in the wrong UNITS.
We need to CONVERT meters (m) into nanometers (nm).
We need to do a UNIT CONVERSION.
4.1 Section Assessment
6. Describe the range of radii of most atoms in nanometers (nm).
5 x 10-11 m
109 nm
x
5x
10(-11 + 9)
=
5x
10(-2)
=
2x
10(-10 + 9)
=
2x
10(-1)
nm
1 m
1
2 x 10-10 m
109 nm
x
1
=
nm
nm
1 m
nm
5 x 10-2 nm to 2 x 10-1 nm
4.1 Section Assessment
7. A sample of copper with a mass of 63.5 grams contains
Calculate the mass of a single copper atom.
So what the heck do you do with these numbers?
63.5 g
= 10.5
6.02 x 1023 atoms
10.54817276
6.02
)
63.5
= 1.05
x 10-23
x 10-22
g/atom
g/atom
6.02 x 1023 atoms.
4.2 Section Assessment
8. What are three types of subatomic particles?
The three kinds of subatomic particles are
the electron, the proton, and the neutron.
All atoms are made merely of different combinations of these three fundamental building
blocks.
Since you are made of atoms, that means that you are made of
protons, neutrons, and electrons.
4.2 Section Assessment
9. How does the Rutherford model describe the structure of atoms?
From his experiments, Rutherford concluded that an atom is made of a positively-charged
nucleus surrounded by a region of empty space in which electrons orbit that nucleus.
Rutherford believed that an atom’s nucleus was very tiny compared to the atom as a whole, and
that, in spite of this, the nucleus is where most of the atom’s mass is.
Thus, according to Rutherford’s interpretation of his experimental results, atoms are made
mostly of empty space.
This implies that all things made of matter, anything that is solid, liquid, or gas, is actually made
mostly of empty space.
4.2 Section Assessment
10. What are the charges and relative masses of the three main subatomic particles?
(Table 4.1 at the top of page 106 summarizes this nicely for you.)
Particle
electron
proton
neutron
Symbol Charge Relative mass
ep+ (or H+!)
n0
1-
1/1840
1+
1
0
1 (actually a little more than that)
4.2 Section Assessment
11. Describe Thomson’s and Millikan’s contributions to atomic theory.
Thomson, through his cathode ray tube experiments, discovered the electron.
Millikan, through his oil drop experiments, determined the charge and mass of the electron.
4.2 Section Assessment
12. Compare Rutherford’s expected outcome of the gold foil experiment with the actual
outcome.
Rutherford expected that the alpha particles he shot at the gold foil would pass through it with
little deflection.
Instead, he found that, although most did shoot straight through with little or no deflection,
some alpha particles were deflected at very large angles, and some alpha particles even
bounced back toward the alpha particle source.
He likened this to shooting a cannonball at a piece of facial tissue and having it bounce back.
Rutherford had no idea that there was anything dense and heavy enough in an atom to bounce
an alpha particle back to where it came from.
4.2 Section Assessment
13. What experimental evidence led Rutherford to conclude that an atom is mostly
empty space?
The great majority of the alpha particles went straight through the gold foil, as though nothing
were there.
4.2 Section Assessment
14. How did Rutherford’s model of the atom differ from Thomson’s?
Thomson thought the atom was a mass of positive charge with negative electrons embedded in
its outer surface.
Rutherford’s model didn’t envision the atom being a big ball of positive charge, but, rather, a
tiny speck of positive charge in the middle of an almost perfectly empty region of space.
Rutherford did not envision electrons as stuck in anything, but, rather, as whizzing through
space, in “orbit” around the positive nucleus. He envisioned the atom as a tiny solar system, in
which the nucleus was like the sun and the electrons were like planets.
#’s 15 – 24 are “Practice
Problems”, so the answers are
in the back of the book.
Look on page R84.
4.3 Section Assessment
25. What distinguishes the atoms of one element from the atoms of another?
The number of protons in an atom determines what element it belongs to.
Number of protons is called “atomic number”.
For instance, all gold atoms have exactly 79 protons in them.
Any atom that has 26 protons in it is, by definition, an iron atom.
4.3 Section Assessment
26. What equation tells you how to calculate the number of neutrons in an atom?
number of neutrons = mass number – atomic number
This is true because
mass number = number of protons + number of neutrons . . .
and atomic number = number of protons
4.3 Section Assessment
27. How do the isotopes of a given element differ from one another?
Isotopes of a given element vary only in the number of neutrons in each atom.
For instance, most carbon atoms are from the isotope carbon-12, but a few are from the isotope
carbon-14.
Carbon-12 atoms and carbon-14 atoms all have 6 protons, but
carbon-12 atoms have only 6 neutrons each, whereas
carbon-14 atoms have 8 neutrons each.
Incidentally, the two extra neutrons in carbon-14 make that isotope radioactive . . . But we’ll
discuss radioactivity later . . .
4.3 Section Assessment
28. How is atomic mass calculated?
Atomic mass is calculated by what is called a “weighted average” method (no pun intended).
The mass of each known isotope of the element is multiplied by the % abundance of that
element.
Because of this, rare isotopes tend to have a very small effect upon the average atomic mass of
an element.
Also, the average atomic mass of the element tends to be very close to the atomic mass of the
most common isotope of that element.
4.3 Section Assessment
29. What makes the periodic table such a useful tool?
By looking at the periodic table, one can predict the chemical and physical properties of an
element by its location on the table. Here are a few examples of this:
*Elements in the same vertical column tend to have the same number of “valence electrons”,
and, therefore, similar bonding properties.
*Elements to the left of the “staircase” are almost all metals, elements to the right almost all
nonmetals, and elements touching the staircase mostly metalloids.
*Elements with high electronegativies and ionization energies tend to be clustered in the upper
right hand corner of the periodic table.
[Don’t burden your brain too much with these examples just yet. We’ll be looking at them more
closely in chapter 6.]
4.3 Section Assessment
30. What does the number represent in the isotope name “platinum-194”? Write the
symbol for this atom using superscripts and subscripts.
A platinum-194 atom has a total of 194 protons and neutrons, combined, in its nucleus.
(194 is the “mass number” of platinum-194.)
Since all platinum atoms have 78 protons, then the symbol for a platinum-194 atoms would be .
..
194
78
Pt
4.3 Section Assessment
31. The atomic masses of elements are generally not whole numbers. Explain why.
The average atomic mass of an element is typically not a whole number precisely because it is
an average atomic mass. Averages tend to have decimal fractions hanging of the ends of them.
An average atomic mass is the weighted average of the atomic masses of all the naturallyoccurring isotopes of the element. Even if the atomic masses of the isotopes were whole
numbers (which they aren’t), the weighted average of those atomic masses would almost
certainly never be a whole number.
[Don’t worry about this question too much. If you get it, great. If you don’t, no biggie. There
are more important concepts for you to master in this class than this one.]
4.3 Section Assessment
32. List the number of protons, neutrons, and electrons in each pair of isotopes.
a.
6
3
Li
7
3
Li
If an atom does have an electric
charge, then it will be written where
the flashing blue squares are.
Protons:
3
3
(Lithium’s atomic number is 3.)
Neutrons:
3
4
(# of neutrons =
mass number – atomic number)
3
(no electrical charge listed, so
# of electrons = # of protons =
atomic number)
Electrons:
3
4.3 Section Assessment
32. List the number of protons, neutrons, and electrons in each pair of isotopes.
b.
42
20
Protons:
Neutrons:
Electrons:
Ca
20
22
20
44
20
Ca
20
24
20
4.3 Section Assessment
32. List the number of protons, neutrons, and electrons in each pair of isotopes.
c.
78
34
Protons:
Neutrons:
Electrons:
Se
34
44
34
80
34
Se
34
46
34
4.3 Section Assessment
33. Name two elements that have properties similar to those of the element calcium
(Ca).
Be (beryllium)
Mg (magnesium)
Ba (barium)
Sr (strontium)
Ra (radium)
If two elements are in the same vertical column of the periodic table, they
probably have similar properties.
Because of this, columns are also known as “families”.
The above-named elements comprise the family known as the . . .
“alkaline earth metals”.